Journal articles on the topic 'Rectifying transient cell'
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1
Zhabyeyev, Pavel, Tatsuya Asai, Sergey Missan, and Terence F. McDonald. "Transient outward current carried by inwardly rectifying K+ channels in guinea pig ventricular myocytes dialyzed with low-K+ solution." American Journal of Physiology-Cell Physiology 287, no. 5 (November 2004): C1396—C1403. http://dx.doi.org/10.1152/ajpcell.00479.2003.
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There have been periodic reports of nonclassic (4-aminopyridine insensitive) transient outward K+ current in guinea pig ventricular myocytes, with the most recent one describing a novel voltage-gated inwardly rectifying type. In the present study, we have investigated a transient outward current that overlaps inward Ca2+ current ( ICa,L) in myocytes dialyzed with 10 mM K+ solution and superfused with Tyrode’s solution. Although depolarizations from holding potential ( Vhp) −40 to 0 mV elicited relatively small inward ICa,L in these myocytes, removal of external K+ or addition of 0.2 mM Ba2+ more than doubled the amplitude of the current. The basis of the enhancement of ICa,L was the suppression of a large transient outward K+ current. Similar enhancement was observed when Vhp was moved to −80 mV and test depolarizations were preceded by short prepulses to −40 mV. Investigation of the time and voltage properties of the outward K+ transient indicated that it was inwardly rectifying and unlikely to be carried by voltage-gated channels. The outward transient was attenuated in myocytes dialyzed with high-Mg2+ solution, accelerated in myocytes dialyzed with 100 μM spermine solution, and abolished with time in myocytes dialyzed with ATP-free solution. These and other findings suggest that the outward transient is a component of classic “time-independent” inwardly rectifying K+ current.
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ZHANG, Zongming, Yufang TANG, and Michael Xi ZHU. "Increased inwardly rectifying potassium currents in HEK-293 cells expressing murine transient receptor potential 4." Biochemical Journal 354, no. 3 (March 8, 2001): 717–25. http://dx.doi.org/10.1042/bj3540717.
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Drosophila transient receptor potential (Trp) and its mammalian homologues are postulated to form capacitative Ca2+ entry or store-operated channels. Here we show that expression of murine Trp4 in HEK 293 cells also leads to an increase in inwardly rectifying K+ currents. No similar increase was found in cell lines expressing Trp1, Trp3 or Trp6. Consistent with typical characteristics of inward rectifiers, the K+ currents in Trp4-expressing cells were blocked by low millimolar concentrations of Cs+ and Ba2+, but not by 1.2mM Ca2+, and were only slightly inhibited by 5mM tetraethylammonium. Single channel recordings of excised inside-out patches revealed the presence of two conducting states of 51pS and 94pS in Trp4-expressing cells. The outward current in the excised patches was blocked by 1mM spermine, but not by 1mM Mg2+. How Trp4 expression causes the increase in the K+ currents is not known. We propose that Trp4 either participates in the formation of a novel K+ channel or up-regulates the expression or activity of endogenous inwardly rectifying K+ channels.
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Vaca, L., A. Licea, and L. D. Possani. "Modulation of cell membrane potential in cultured vascular endothelium." American Journal of Physiology-Cell Physiology 270, no. 3 (March 1, 1996): C819—C824. http://dx.doi.org/10.1152/ajpcell.1996.270.3.c819.
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The present study explores the role of different ionic conductances in the regulation of membrane potential under resting conditions and after bradykinin (BK) or thapsigargin (TG) stimulation of cultured bovine aortic endothelial cells. Under resting conditions, the cell membrane potential observed was -62+/- 5 mV. The main conductance under these conditions is an inwardly rectifying potassium (IRK) channel. Application of 50 nM BK induced a transient hyperpolarization to -87 +/- 4 mV followed by sustained depolarization to -35 +/- 5 mV. The transient hyperpolarization was eliminated by 1 microM noxiustoxin, a blocker of calcium-activated postassium channels (K(Ca)). the sustained depolarization induced by BK was prevented by incubating the cells with the calcium channel blocker lanthanum. TG evoked a similar response in membrane potential, with the exception that the onset of the hyperpolarization was slower compared with BK. The results presented here indicate that the cell resting potential is maintained at -62 +/- 2 mV by the IRK channel. BK or TG stimulation induces a transient hyperpolarization of approximately -20 mV produced by activation of a KCa. This hyperpolarization is followed by a sustained depolarization produced by activation of a calcium-selective channel sensitive to lanthanum.
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WANG, SHU-JIE, LAI-HUA XIE, BIN HENG, and YAN-QIANG LIU. "Classification of potassium and chlorine ionic currents in retinal ganglion cell line (RGC-5) by whole-cell patch clamp." Visual Neuroscience 29, no. 6 (October 30, 2012): 275–82. http://dx.doi.org/10.1017/s0952523812000272.
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AbstractRetinal ganglion cell line (RGC-5) has been widely used as a valuable model for studying pathophysiology and physiology of retinal ganglion cells in vitro. However, the electrophysiological characteristics, especially a thorough classification of ionic currents in the cell line, remain to be elucidated in details. In the present study, we determined the resting membrane potential (RMP) in RGC-5 cell line and then identified different types of ionic currents by using the whole-cell patch-clamp technique. The RMP recorded in the cell line was between −30 and −6 mV (−17.6 ± 2.6 mV, n = 10). We observed the following voltage-gated ion channel currents: (1) inwardly rectifying Cl− current (ICl,ir), which could be blocked by Zn2+; (2) Ca2+-activated Cl− current (ICl,Ca), which was sensitive to extracellular Ca2+ and could be inhibited by disodium 4,4’-diisothiocyanatostilbene-2,2’-disulfonate; (3) inwardly rectifying K+ currents (IK1), which could be blocked by Ba2+; (4) a small amount of delayed rectifier K+ current (IK). On the other hand, the voltage-gated sodium channels current (INa) and transient outward potassium channels current (IA) were not observed in this cell line. These results further characterize the ionic currents in the RGC-5 cell line and are beneficial for future studies especially on ion channel (patho)physiology and pharmacology in the RGC-5 cell line.
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Masetto, S., P. Perin, A. Malusà, G. Zucca, and P. Valli. "Membrane Properties of Chick Semicircular Canal Hair Cells In Situ During Embryonic Development." Journal of Neurophysiology 83, no. 5 (May 1, 2000): 2740–56. http://dx.doi.org/10.1152/jn.2000.83.5.2740.
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The electrophysiological properties of developing vestibular hair cells have been investigated in a chick crista slice preparation, from embryonic day 10 ( E10) to E21 (when hatching would occur). Patch-clamp whole-cell experiments showed that different types of ion channels are sequentially expressed during development. An inward Ca2+ current and a slow outward rectifying K+current ( I K(V)) are acquired first, at or before E10, followed by a rapid transient K+current ( I K(A)) at E12, and by a small Ca-dependent K+ current ( I KCa) at E14. Hair cell maturation then proceeds with the expression of hyperpolarization-activated currents: a slow I h appears first, around E16, followed by the fast inward rectifier I K1around E19. From the time of its first appearance, I K(A) is preferentially expressed in peripheral ( zone 1) hair cells, whereas inward rectifying currents are preferentially expressed in intermediate ( zone 2) and central ( zone 3) hair cells. Each conductance conferred distinctive properties on hair cell voltage response. Starting from E15, some hair cells, preferentially located at the intermediate region, showed the amphora shape typical of type I hair cells. From E17 (a time when the afferent calyx is completed) these cells expressed I K, L, the signature current of mature type I hair cells. Close to hatching, hair cell complements and regional organization of ion currents appeared similar to those reported for the mature avian crista. By the progressive acquisition of different types of inward and outward rectifying currents, hair cell repolarization after both positive- and negative-current injections is greatly strengthened and speeded up.
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Dukes, I. D., and M. Morad. "Tedisamil inactivates transient outward K+ current in rat ventricular myocytes." American Journal of Physiology-Heart and Circulatory Physiology 257, no. 5 (November 1, 1989): H1746—H1749. http://dx.doi.org/10.1152/ajpheart.1989.257.5.h1746.
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The action of tedisamil, a new bradycardiac agent with antiarrhythmic properties, was investigated in single rat ventricular myocytes using the whole cell voltage-clamp technique. Under current clamp conditions, 1-20 microM tedisamil caused marked prolongations of the action potential. Over the same concentration range, in voltage-clamped myocytes, tedisamil suppressed the transient outward current (ito) and enhanced its inactivation in a dose-dependent manner. The half-maximal dose for the effect of tedisamil on ito was approximately 6 microM. Tedisamil had no significant effects on the inwardly rectifying potassium current and calcium current but did suppress the sodium current at concentrations greater than 20 microM. Our findings suggest that tedisamil represents a new type of antiarrhythmic agent that primarily suppresses the transient outward K+ current.
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Gao, Feng, Lin-Jie Xu, Yuan Zhao, Xing-Huai Sun, and Zhongfeng Wang. "K+ Channels of Müller Glial Cells in Retinal Disorders." CNS & Neurological Disorders - Drug Targets 17, no. 4 (July 6, 2018): 255–60. http://dx.doi.org/10.2174/1871527317666180202114233.
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Background & Objective: Müller cell is the major type of glial cell in the vertebrate retina. Müller cells express various types of K+ channels, such as inwardly rectifying K+ (Kir) channels, big conductance Ca2+-activated K+ (BKCa) channels, delayed rectifier K+ channels (KDR), and transient A-type K+ channels. These K+ channels play important roles in maintaining physiological functions of Müller cells. Under some retinal pathological conditions, the changed expression and functions of K+ channels may contribute to retinal pathogenesis. Conclusion: In this article, we reviewed the physiological properties of K+ channels in retinal Müller cells and the functional changes of these channels in retinal disorders.
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Van Goor, Fredrick, Dragoslava Zivadinovic, and Stanko S. Stojilkovic. "Differential Expression of Ionic Channels in Rat Anterior Pituitary Cells." Molecular Endocrinology 15, no. 7 (July 1, 2001): 1222–36. http://dx.doi.org/10.1210/mend.15.7.0668.
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Abstract Secretory anterior pituitary cells are of the same origin, but exhibit cell type-specific patterns of spontaneous intracellular Ca2+ signaling and basal hormone secretion. To understand the underlying ionic mechanisms mediating these differences, we compared the ionic channels expressed in somatotrophs, lactotrophs, and gonadotrophs from randomly cycling female rats under identical cell culture and recording conditions. Our results indicate that a similar group of ionic channels are expressed in each cell type, including transient and sustained voltage-gated Ca2+ channels, tetrodotoxin-sensitive Na+ channels, transient and delayed rectifying K+ channels, and multiple Ca2+-sensitive K+ channel subtypes. However, there were marked differences in the expression levels of some of the ionic channels. Specifically, lactotrophs and somatotrophs exhibited low expression levels of tetrodotoxin-sensitive Na+ channels and high expression levels of the large-conductance, Ca2+-activated K+ channel compared with those observed in gonadotrophs. In addition, functional expression of the transient K+ channel was much higher in lactotrophs and gonadotrophs than in somatotrophs. Finally, the expression of the transient voltage-gated Ca2+ channels was higher in somatotrophs than in lactotrophs and gonadotrophs. These results indicate that there are cell type-specific patterns of ionic channel expression, which may be of physiological significance for the control of Ca2+ homeostasis and secretion in unstimulated and receptor-stimulated anterior pituitary cells.
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Solessio, Eduardo, Kevin Rapp, Ido Perlman, and Eric M. Lasater. "Spermine Mediates Inward Rectification in Potassium Channels of Turtle Retinal Müller Cells." Journal of Neurophysiology 85, no. 4 (April 1, 2001): 1357–67. http://dx.doi.org/10.1152/jn.2001.85.4.1357.
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Retinal Müller cells are highly permeable to potassium as a consequence of their intrinsic membrane properties. Therefore these cells are able to play an important role in maintaining potassium homeostasis in the vertebrate retina during light-induced neuronal activity. Polyamines and other factors present in Müller cells have the potential to modulate the rectifying properties of potassium channels and alter the Müller cells capacity to siphon potassium from the extracellular space. In this study, the properties of potassium currents in turtle Müller cells were investigated using whole cell voltage-clamp recordings from isolated cells. Overall, the currents were inwardly rectifying. Depolarization elicited an outward current characterized by a fast transient that slowly recovered to a steady level along a double exponential time course. On hyperpolarization the evoked inward current was characterized by an instantaneous onset (or step) followed by a slowly developing sustained inward current. The kinetics of the time-dependent components (block of the transient outward current and slowly developing inward current) were dependent on holding potential and changes in the intracellular levels of magnesium ions and polyamines. In contrast, the instantaneous inward and the sustained outward currents were ohmic in character and remained relatively unaltered with changes in holding potential and concentration of applied spermine (0.5–2 mM). Our data suggest that cellular regulation in vivo of polyamine levels can differentially alter specific aspects of potassium siphoning by Müller cells in the turtle retina by modulating potassium channel function.
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Christoforou, N., J. D. Leslie, and S. Damaskinos. "Characterization of CdS–CuInSe2 solar cells by current–voltage, capacitance–voltage, and capacitance-transient measurements." Canadian Journal of Physics 65, no. 8 (August 1, 1987): 966–71. http://dx.doi.org/10.1139/p87-152.
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CdS–CuInSe2 solar cells, which have an efficiency of 9%, have been studied by current–voltage, capacitance–voltage, and capacitance-transient measurements over the temperature range 90–380 K. Deep-level transient spectroscopy analysis of the capacitance transient measurements reveals one majority carrier trap with an activation energy of 0.70 ± 0.02 eV. Although the present experiment cannot establish definitely if the trap is in the CdS or CuInSe2 layer, arguments are presented that it is a hole trap in the p-type CuInSe2 layer. Current–voltage measurements indicate a reversible increase in the reverse-bias leakage current with increasing temperature above 300 K. Evidence is presented that suggests that the rectifying barrier height in the CdS–CuInSe2 solar cell decreases rapidly with temperature above 300 K. Capacitance versus voltage measurements suggest that the depiction layer being studied is primarily in the CuInSe2, but the temperature dependence of the ionized charge concentration N(x) cannot be totally explained although one possible cause is suggested.
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Friedrich, F., H. Weiss, M. Paulmichl, and F. Lang. "Activation of potassium channels in renal epithelioid cells (MDCK) by extracellular ATP." American Journal of Physiology-Cell Physiology 256, no. 5 (May 1, 1989): C1016—C1021. http://dx.doi.org/10.1152/ajpcell.1989.256.5.c1016.
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Extracellular ATP has been shown to stimulate transepithelial chloride transport in confluent Madin-Darby canine kidney (MDCK) cell layers and to enhance potassium conductance in subconfluent MDCK cells. The present study has been performed to test for the effect of extracellular ATP on channel activity in patches from subconfluent MDCK cells. Within 8 s, addition of extracellular ATP (10 mumol/l) leads to a sustained, but fully reversible, appearance of potassium-selective channels in cell-attached patches [increase of open probability from 0.03 +/- 0.02 (n = 10) to 0.50 +/- 0.07 (n = 6)]. With the use of pipettes filled with 145 mmol/l KCl, inwardly rectifying property of the channels is disclosed with a single-channel conductance of 65.7 +/- 3.1 pS (n = 9) at zero potential difference between pipette and bath and with a reversal potential of 75.4 +/- 2.0 mV (n = 5; pipette negative vs. reference in the bath). The open probability of the channels is not significantly modified by altering pipette potential from -50 mV, pipette positive, to 50 mV, pipette negative. At extracellular calcium activities of less than 10 nmol/l, ATP leads to a transient activation of channels. In conclusion, extracellular ATP activates inwardly rectifying potassium channels in the cell membrane of subconfluent MDCK cells. A sustained activation of the channels requires the presence of extracellular calcium and is probably mediated by increases in intracellular calcium.
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Babes, Alexandru, Cristian Neacsu, Michael JM Fischer, and Karl Messlinger. "Sumatriptan activates TRPA1." Cephalalgia Reports 2 (January 1, 2019): 251581631984715. http://dx.doi.org/10.1177/2515816319847155.
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Background: Migraine therapy with sumatriptan may cause adverse side effects like pain at the injection site, muscle pain, and transient aggravation of headaches. In animal experiments, sumatriptan excited or sensitized slowly conducting meningeal afferents. We hypothesized that sumatriptan may activate transduction channels of the “irritant receptor,” the transient receptor potential ankyrin type (TRPA1) expressed in nociceptive neurons. Methods: Calcium microfluorometry was performed in HEK293t cells transfected with human TRPA1 (hTRPA1) or a mutated channel (TRPA1-3C) and in dissociated trigeminal ganglion neurons. Membrane currents were recorded in the whole-cell patch clamp configuration. Results: Sumatriptan (10 and 400 µM) evoked calcium transients in hTRPA1-expressing HEK293t cells also activated by the TRPA1 agonist carvacrol (100 µM). In TRPA1-3C-expressing HEK293t cells, sumatriptan had hardly any effect. In rat trigeminal ganglion neurons, sumatriptan, carvacrol, and the transient receptor potential vanillod type 1 agonist capsaicin (1 µM) generated robust calcium signals. All sumatriptan-sensitive neurons (8% of the sample) were also activated by carvacrol (14%) and capsaicin (48%). In HEK293-hTRPA1 cells, sumatriptan (100 µM) evoked outwardly rectifying currents, which were almost completely inhibited by the TRPA1 antagonist HC-030031 (10 µM). Conclusion: Sumatriptan activates TRPA1 channels inducing calcium inflow and membrane currents. TRPA1-dependent activation of primary afferents may explain the painful side effects of sumatriptan.
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Kunze, D. L., W. G. Sinkins, L. Vaca, and W. P. Schilling. "Properties of single Drosophila Trpl channels expressed in Sf9 insect cells." American Journal of Physiology-Cell Physiology 272, no. 1 (January 1, 1997): C27—C34. http://dx.doi.org/10.1152/ajpcell.1997.272.1.c27.
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The transient receptor potential (trp)-like (trpl) gene is thought to encode an ion channel important for signal transduction in Drosophila photoreceptor cells. Consistent with this hypothesis, heterologous expression of the trpl-encoded protein (Trpl) is associated with the appearance of an outwardly rectifying, nonselective cation current. In the present study, single channels were recorded in cell-attached, inside-out, and outside-out membrane patches from Sf9 insect cells infected with recombinant baculovirus-containing trpl cDNA under control of the polyhedrin promoter. The single-channel current-voltage relationship was linear from -100 to +80 mV with a slope conductance of 89-110 pS. The probability of opening was voltage sensitive, increasing at positive potentials contributing to the outwardly rectifying properties of the whole cell currents. The single channels 1) were never observed in Sf9 cells infected with recombinant baculovirus containing the B2 bradykinin receptor cDNA or in noninfected Sf9 cells; 2) appear at the same time postinfection as the Trpl whole cell current; 3) were nonselective with respect to Na+, Ca2+, and Ba2+; 4) were blocked by 1-2 mM La3+ and Gd3+ (but not 10 microM); and 5) were blocked by 4-8 mM Mg2+. The single Trpl channel activity increased spontaneously with time after patch formation, and the activity was further increased by application of bradykinin to cells expressing both the B2 bradykinin receptor and the Trpl protein. These results suggest that this single-channel activity reflects expression of the Trpl protein and provides conclusive evidence that trpl encodes a nonselective cation channel consistent with its proposed role in Drosophila phototransduction.
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Li, G. "A Novel Inwardly-Rectifying Transient Outward Potassium Current Plays an Important Role in Maintaining Cell Excitability of Canine Myocardium." Journal of the American College of Cardiology 31, no. 2 (February 1998): 472A. http://dx.doi.org/10.1016/s0735-1097(97)88054-0.
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Li, G. R. "A novel inwardly-rectifying transient outward potassium current plays an important role in maintaining cell excitability of canine myocardium." Journal of the American College of Cardiology 31 (February 1998): 472. http://dx.doi.org/10.1016/s0735-1097(98)80405-1.
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Tompkins, John D., and Rodney L. Parsons. "Exocytotic release of ATP and activation of P2X receptors in dissociated guinea pig stellate neurons." American Journal of Physiology-Cell Physiology 291, no. 5 (November 2006): C1062—C1071. http://dx.doi.org/10.1152/ajpcell.00472.2005.
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Activation of P2X receptors by a Ca2+- and soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein-dependent release of ATP was measured using patch-clamp recordings from dissociated guinea pig stellate neurons. Asynchronous transient inward currents (ASTICs) were activated by depolarization or treatment with the Ca2+ ionophore ionomycin (1.5 and 3 μM). During superfusion with a HEPES-buffered salt solution containing 2.5 mM Ca2+, depolarizing voltage steps (−60 to 0 mV, 500 ms) evoked ASTICs on the decaying phase of a larger, transient inward current. Equimolar substitution of Ba2+ for Ca2+ augmented the postdepolarization frequency of ASTICs, while eliminating the larger transient current. Perfusion with an ionomycin-containing solution elicited a sustained activation of ASTICs, allowing quantitative analysis over a range of holding potentials. Under these conditions, increasing extracellular [Ca2+] to 5 mM increased ASTIC frequency, whereas no events were observed following replacement of Ca2+ with Mg2+, demonstrating a Ca2+ requirement. ASTICs were Na+ dependent, inwardly rectifying, and reversed near 0 mV. Treatment with the nonselective purinergic receptor antagonist pyridoxal phosphate-6-azophenyl-2′,4′-disulfonic acid (PPADS) (10 μM) blocked all events under both conditions, whereas the ganglionic nicotinic antagonist hexamethonium (100 μM and 1 mM) had no effect. PPADS also blocked the macroscopic inward current evoked by exogenously applied ATP (300 μM). The presence of botulinum neurotoxin E (BoNT/E) in the whole-cell recording electrode significantly attenuated the ionomycin-induced ASTIC activity, whereas phorbol ester treatment potentiated this activity. These results suggest that ASTICs are mediated by vesicular release of ATP and activation of P2X receptors.
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Shibata, E. F., T. Drury, H. Refsum, V. Aldrete, and W. Giles. "Contributions of a transient outward current to repolarization in human atrium." American Journal of Physiology-Heart and Circulatory Physiology 257, no. 6 (December 1, 1989): H1773—H1781. http://dx.doi.org/10.1152/ajpheart.1989.257.6.h1773.
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Conventional microelectrode recordings combined with enzymatic cell dispersion methods and a single microelectrode voltage-clamp technique were used to record transmembrane action potentials and ionic currents in isolated single myocytes and in excised segments of human right atrium. Recordings of the outward current(s), which is responsible for the resting potential and early repolarization of the action potential in human right atrium, consistently showed that this tissue has 1) a relatively small inwardly rectifying background potassium current (IK1) which generates the resting potential in mammalian ventricular tissue and Purkinje fibers, and 2) a large time- and voltage-dependent, but Ca2(+)-independent, transient outward current. A somewhat similar K+ current was originally described in neurons and recently has also been identified in a variety of mammalian cardiac tissues. As expected from previous work, this transient outward current in human atrium is blocked by 4-aminopyridine (4-AP; 0.5 mM) and exhibits time- and voltage-dependent inactivation and reactivation. Measurements of action potential shape changes and phasic tension as a function of stimulus frequency, or after 4-AP application, show that in human atrium this current can produce pronounced changes in both the early repolarization of the action potential and force generation.
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Sontheimer, H., and S. G. Waxman. "Expression of voltage-activated ion channels by astrocytes and oligodendrocytes in the hippocampal slice." Journal of Neurophysiology 70, no. 5 (November 1, 1993): 1863–73. http://dx.doi.org/10.1152/jn.1993.70.5.1863.
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1. Using patch-clamp recordings, expression of voltage-activated ion channels by identified glial cells in situ was studied in hippocampal slices derived from 5- to 24-day-old rats. Glial cells were filled with Lucifer yellow during recording, and were identified by staining for glial fibrillary acidic protein (GFAP). Of 105 cells presumed to be glial cells from which recordings were obtained, 40 were identified as astrocytes and 22 as oligodendrocytes. 2. Astrocytes in the hippocampal slice express three types of K+ current, singly or in combination: delayed rectifying currents (Kd), transient "A"-type currents (Ka) and inward-rectifying currents (Kir). Kd-like currents were observed in 88% of astrocytes recorded; these currents activated rapidly with a threshold of -40 mV and did not inactivate during a 10- to 30-ms pulse. A-type transient K+ currents were identified in 43% of astrocytes and required a negative holding potential (-110 mV) for activation. These activated at about -50 mV, and their time constant of inactivation was close to 10 ms. In 20% of astrocytes recorded in slices from animals > 7 days old, inwardly rectifying K+ currents were observed in addition to Kd or Ka. 3. Voltage-activated Na+ currents were observed in 11 of the 105 cells, and 5 of these were identified as astrocytes by GFAP staining. These were located in either stratum oriens or close to the granule cell layer in CA3. Na+ current densities ranged from 1.5 to 90 pA/pF. Voltage steps more positive than -40 mV were required for activation, peaks were close to -10 mV, and time to peak was between 300 and 800 microseconds. Extrapolated current reversal potentials were close to the theoretical Na+ equilibrium potential. 4. Spontaneous action potentials were never observed in any of the hippocampal astrocytes recorded, including those astrocytes that expressed Na+ currents. Additionally, action potentials could not be induced by current injections. By contrast, 26 hippocampal neurons recorded in the same slices showed both spontaneous and elicited action potentials as well as synaptic currents. 5. Oligodendrocytes, identified by lack of GFAP staining and cell morphology, had resting potentials ranging between -25 and -82 mV in 5 mM KCl. In approximately 50% of oligodendrocytes, time-dependent currents were not observed and only time-independent currents with linear current-voltage curves were recorded. In the remaining 50% of oligodendrocytes, time- and voltage-dependent K+ currents characterized by inward rectification were present.(ABSTRACT TRUNCATED AT 400 WORDS)
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Watsky, M. A. "Nonselective cation channel activation during wound healing in the corneal endothelium." American Journal of Physiology-Cell Physiology 268, no. 5 (May 1, 1995): C1179—C1185. http://dx.doi.org/10.1152/ajpcell.1995.268.5.c1179.
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Rabbit corneas were injured by mechanical or thermal trauma. At several time points after wounding, corneal endothelial cells were isolated and their ion channels examined using standard and amphotericin perforated-patch whole cell patch-clamp configurations. Within 15-24 h after mechanical or thermal trauma, a nonselective cation current was observed in 79% of the cells examined that was not present in unwounded or sham-wounded corneas. By 73 h postwounding, the current was present in only 10% of the cells examined. The wound healing-induced current is outwardly rectifying, activates at depolarized voltages, shows no sign of inactivation, and is inhibited by flufenamic acid, quinidine, and acetate. In addition to this new current, it was observed that endothelial cells from freeze-wounded corneas no longer expressed the transient K+ current seen in control, sham, and mechanically wounded corneas. Corneal endothelial superfusion experiments found no significant difference in swelling rates between control and flufenamic acid-superfused wounded corneas, indicating that the wound healing-induced channel is not involved in the stromal hydration maintenance function of the corneal endothelium.
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Fritsch, J., and A. Edelman. "Osmosensitivity of the hyperpolarization-activated chloride current in human intestinal T84 cells." American Journal of Physiology-Cell Physiology 272, no. 3 (March 1, 1997): C778—C786. http://dx.doi.org/10.1152/ajpcell.1997.272.3.c778.
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The osmosensitivity of the hyperpolarization-activated chloride current (I(Clhyp)) in T84 cells was studied using the whole cell patch-clamp recording configuration. Hypotonicity is known to activate an outwardly rectifying chloride current (HIORC) distinct from I(Clhyp) in these cells. The differing sensitivities of HIORC and I(Clhyp) toward inhibitors (1,9-dideoxyforskolin blocked HIORC but not I(Clhyp), and Cd2+ inhibited I(Clhyp) but not HIORC) allowed us to investigate the osmoregulation of I(Clhyp). Hypotonicity induced an increase in I(Clhyp) amplitude. Protein phosphatase inhibitors prevented this effect, and hypotonic solutions became slightly inhibitory. Hypertonicity resulted in a transient increase in I(Clhyp) amplitude followed by a large decrease. The complex responses of I(Clhyp) to osmotic changes indicate that these signals affect the same channel via multiple transduction pathways. The responses of I(Clhyp) to hypotonicity have features in common with the responses of ClC-2 channels expressed in Xenopus oocytes (activation) and with hyperpolarization-activated chloride currents in other cell types, such as osteoblasts and mandibular duct cells (inhibition).
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Mitchell, C. H., J. J. Zhang, L. Wang, and T. J. Jacob. "Volume-sensitive chloride current in pigmented ciliary epithelial cells: role of phospholipases." American Journal of Physiology-Cell Physiology 272, no. 1 (January 1, 1997): C212—C222. http://dx.doi.org/10.1152/ajpcell.1997.272.1.c212.
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The whole cell recording technique was used to examine an outwardly rectifying chloride current activated by hypotonic shock in bovine pigmented ciliary epithelial (PCE) cells. Removal of internal and external Ca2+ did not affect the activation of these currents, but they were abolished by the phospholipase C inhibitor neomycin. The current was blocked by 5-nitro-2-(3-phenylpropylamino)benzoic acid, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid, and 4,4'-disothiocyanostilbene-2,2'-disulfonic acid (DIDS) in a voltage-dependent manner, but tamoxifen, dideoxyforskolin, and quinidine did not affect it. This blocking profile differs from that of the volume-sensitive chloride channel in neighboring nonpigmented ciliary epithelial cells (Wu, J., J. J. Zhang, H. Koppel, and T. J. C. Jacob, J. Physiol, Lond. 491: 743-755, 1996), and this difference implies that the volume responses of the two cell types are mediated by different chloride channels (Jacob, T. J. C., and J. J. Zhang. J. Physiol. Lond. In press). Intracellular administration of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) to PCE cells induced a transient, time-independent, outwardly rectifying chloride current that closely resembled the current activated by hypotonic shock. DIDS produced a voltage-dependent block of the GTP gamma S-activated current similar to the block of the hypotonically activated current. Intracellular neomycin completely prevented activation of this current as did incubation of the cells in calphostin C. and inhibitor of protein kinase C (PKC). Removal of Ca2+ did not affect activation of the current by GTP gamma S but extended the duration of the response. Inhibition of phospholipase A2 (PLA2) with p-bromophenacyl bromide prevented the activation of the hypotonically induced current and also inhibited the current once activated by hypotonic solution. The findings imply that the hypotonic response in PCE cells is mediated by both phospholipase C (PLC) and PLA2. Both phospholipases generate arachidonic acid, and, in addition, the PLC pathway regulates the PLA2 pathway via a PKC-dependent phosphorylation of PLA2.
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Lasater, E. M. "Ionic currents of cultured horizontal cells isolated from white perch retina." Journal of Neurophysiology 55, no. 3 (March 1, 1986): 499–513. http://dx.doi.org/10.1152/jn.1986.55.3.499.
Full textAbstract:
Horizontal cells from the retinas of white perch were isolated and maintained in cell culture for 3 days to 3 wk. Four morphologically distinct types of horizontal cells could be identified in culture and were labeled types H1, H2, H3, and H4. Whole-cell patch-clamp techniques were used to study the ionic currents present in the four cell types. In all cells, depolarizing commands above threshold elicited a fast-inward current followed by an outward current. The fast-inward current was abolished by tetrodotoxin (TTX) or 0 Na+ Ringer's, indicating the current was carried by Na+. In H1, H2, and H3 cells, the outward current, carried by K+, consisted of two components: a transient current (IA), blockable with 4-aminopyridine (4-AP), tetraethylammonium (TEA), or intracellular cesium and a sustained current that could be blocked with TEA. The H4 cell had only the sustained current. An inward rectifying K+ current (anomalous rectifier) was observed in the four cell types. The current was sensitive to the extracellular K+ concentration. Its activation showed two components: an instantaneous component and a slower component. The slow component becomes faster with greater hyperpolarizations. The four cell types possessed a small, sustained Ca2+ current that, under normal conditions, was masked by the inward Na+ current and outward K+ currents.
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Guilbert, Arnaud, Mathieu Gautier, Isabelle Dhennin-Duthille, Nathalie Haren, Henri Sevestre, and Halima Ouadid-Ahidouch. "Evidence that TRPM7 is required for breast cancer cell proliferation." American Journal of Physiology-Cell Physiology 297, no. 3 (September 2009): C493—C502. http://dx.doi.org/10.1152/ajpcell.00624.2008.
Full textAbstract:
Because transient receptor potential (TRP) channels have been implicated in tumor progression, we have investigated the potential role of TRPM7 channel in breast cancer cell proliferation. Under whole cell patch clamp, a Mg2+-inhibited cationic (MIC) current was observed in MCF-7 cells. This current was characterized by an inward current and a strong outward rectifying current that were both inhibited in a concentration-dependent manner by the presence of intracellular Mg2+ or Mg2+-ATP. The inward current was reduced by La3+, and the outward current was sensitive to 2-aminoethoxydiphenyl borate (2-APB), spermine, La3+, and flufenamic acid. Importantly, a similar MIC current was also recorded in the primary culture of human breast cancerous epithelial cells (hBCE). Moreover, TRPM7 transcripts were found in both hBCE and MCF-7 cells. In MCF-7 cells, the MIC current was inhibited by TRPM7 small interfering RNA. Interestingly, we found that cell proliferation and intracellular Ca2+ concentration were also reduced by TRPM7 silencing in MCF-7 cells. TRPM7 channels were also found in both human breast cancer and healthy tissues. Importantly, TRPM7 channel was overexpressed in grade III breast cancer samples associated with important Ki67 or tumor size. Our findings strongly suggest that TRPM7 is involved in the proliferative potentiality of breast cancer cells, probably by regulating Ca2+ influx.
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Jung, Silke, Rainer Strotmann, Günter Schultz, and Tim D. Plant. "TRPC6 is a candidate channel involved in receptor-stimulated cation currents in A7r5 smooth muscle cells." American Journal of Physiology-Cell Physiology 282, no. 2 (February 1, 2002): C347—C359. http://dx.doi.org/10.1152/ajpcell.00283.2001.
Full textAbstract:
To investigate the possible role of members of the mammalian transient receptor potential (TRP) channel family (TRPC1–7) in vasoconstrictor-induced Ca2+ entry in vascular smooth muscle cells, we studied [Arg8]-vasopressin (AVP)-activated channels in A7r5 aortic smooth muscle cells. AVP induced an increase in free cytosolic Ca2+ concentration ([Ca2+]i) consisting of Ca2+ release and Ca2+ influx. Whole cell recordings revealed the activation of a nonselective cation current with a doubly rectifying current-voltage relation strikingly similar to those described for some heterologously expressed TRPC isoforms. The current was also stimulated by direct activation of G proteins as well as by activation of the phospholipase Cγ-coupled platelet-derived growth factor receptor. Currents were not activated by store depletion or increased [Ca2+]i. Application of 1-oleoyl-2-acetyl- sn-glycerol stimulated the current independently of protein kinase C, a characteristic property of the TRPC3/6/7 subfamily. Like TRPC6-mediated currents, cation currents in A7r5 cells were increased by flufenamate. Northern hybridization revealed mRNA coding for TRPC1 and TRPC6. We therefore suggest that TRPC6 is a molecular component of receptor-stimulated Ca2+-permeable cation channels in A7r5 smooth muscle cells.
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Kashiwagi, S., M. Suematsu, Y. Wakabayashi, N. Kawada, M. Tachibana, A. Koizumi, M. Inoue, Y. Ishimura, and A. Kaneko. "Electrophysiological characterization of cultured hepatic stellate cells in rats." American Journal of Physiology-Gastrointestinal and Liver Physiology 272, no. 4 (April 1, 1997): G742—G750. http://dx.doi.org/10.1152/ajpgi.1997.272.4.g742.
Full textAbstract:
This study aimed to examine electrophysiological properties of cultured rat hepatic stellate cells (HSCs) using the whole cell configuration of patch-clamp technique. At least three different current components were identified. First, when the membrane was depolarized to voltages more positive than -40 mV, a transient outward K+ current was evoked. Second, membrane hyperpolarization below -60 mV evoked a sustained and inward-rectifying K+ current. The third component was a current flowing outward, which was activated when the cell was depolarized more positively than 0 mV. The channel for this current allowed Na+, K+, and Cl- to pass nonspecifically, suggesting the presence of hemi gap-junctional channel. Furthermore, a laser photobleaching technique revealed the presence of gap junctions between adjacent HSCs. A voltage-gated Ca2+ current, which is known to occur in smooth muscle cells, was searched for but was not detectable. These results suggest that membrane potential of HSCs is determined specifically by the two distinct K+ channels and by an intercellular mechanism involving gap-junctional communication.
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Buchholtz, F., J. Golowasch, I. R. Epstein, and E. Marder. "Mathematical model of an identified stomatogastric ganglion neuron." Journal of Neurophysiology 67, no. 2 (February 1, 1992): 332–40. http://dx.doi.org/10.1152/jn.1992.67.2.332.
Full textAbstract:
1. The ionic currents in the lateral pyloric (LP) cell of the stomatogastric ganglion (STG) described in the preceding paper of the rock crab Cancer borealis were fit with a set of differential equations that describe their voltage, time, and Ca2+ dependence. The voltage-dependent currents modeled are a delayed rectifier-like current, id; a Ca(2+)-activated outward current, io(Ca); a transient A-like current, iA; a Ca2+ current, iCa; an inwardly rectifying current, ih; and a fast tetrodotoxin (TTX)-sensitive Na+ current, iNa. 2. A single-compartment, isopotential model of the LP cell was constructed from the six voltage-dependent currents, a voltage-independent leak current il, a Ca2+ buffering system, and the membrane capacitance. 3. The behavior of the model LP neuron was compared with that of the biological neuron by simulating physiological experiments carried out in both voltage-clamp and current-clamp modes. The model and biological neurons show similar action-potential shapes, durations, steady-state current-voltage (I-V) curves, and respond to injected current in a comparable way.
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Costantin, James L., and Andrew C. Charles. "Modulation of Ca2+ Signaling by K+Channels in a Hypothalamic Neuronal Cell Line (GT1–1)." Journal of Neurophysiology 85, no. 1 (January 1, 2001): 295–304. http://dx.doi.org/10.1152/jn.2001.85.1.295.
Full textAbstract:
The pulsatile release of gonadotropin releasing hormone (GnRH) is driven by the intrinsic activity of GnRH neurons, which is characterized by bursts of action potentials correlated with oscillatory increases in intracellular Ca2+. The role of K+ channels in this spontaneous activity was studied by examining the effects of commonly used K+ channel blockers on K+currents, spontaneous action currents, and spontaneous Ca2+signaling. Whole-cell recordings of voltage-gated outward K+ currents in GT1–1 neurons revealed at least two different components of the current. These included a rapidly activating transient component and a more slowly activating, sustained component. The transient component could be eliminated by a depolarizing prepulse or by bath application of 1.5 mM 4-aminopyridine (4-AP). The sustained component was partially blocked by 2 mM tetraethylammonium (TEA). GT1–1 cells also express inwardly rectifying K+ currents ( I K(IR)) that were activated by hyperpolarization in the presence of elevated extracellular K+. These currents were blocked by 100 μM Ba2+ and unaffected by 2 mM TEA or 1.5 mM 4-AP. TEA and Ba2+ had distinct effects on the pattern of action current bursts and the resulting Ca2+ oscillations. TEA increased action current burst duration and increased the amplitude of Ca2+ oscillations. Ba2+ caused an increase in the frequency of action current bursts and Ca2+oscillations. These results indicate that specific subtypes of K+ channels in GT1–1 cells can have distinct roles in the amplitude modulation or frequency modulation of Ca2+signaling. K+ current modulation of electrical activity and Ca2+ signaling may be important in the generation of the patterns of cellular activity responsible for the pulsatile release of GnRH.
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Cooper, Bonnie, Barry B. Lee, and Dingcai Cao. "Macaque retinal ganglion cell responses to visual patterns: harmonic composition, noise, and psychophysical detectability." Journal of Neurophysiology 115, no. 6 (June 1, 2016): 2976–88. http://dx.doi.org/10.1152/jn.00411.2015.
Full textAbstract:
The goal of these experiments was to test how well cell responses to visual patterns can be predicted from the sinewave tuning curve. Magnocellular (MC) and parvocellular (PC) ganglion cell responses to different spatial waveforms (sinewave, squarewave, and ramp waveforms) were measured across a range of spatial frequencies. Sinewave spatial tuning curves were fit with standard Gaussian models. From these fits, waveforms and spatial tuning of a cell's responses to the other waveforms were predicted for different harmonics by scaling in amplitude for the power in the waveform's Fourier expansion series over spatial frequency. Since higher spatial harmonics move at a higher temporal frequency, an additional scaling for each harmonic by the MC (bandpass) or PC (lowpass) temporal response was included, together with response phase. Finally, the model included a rectifying nonlinearity. This provided a largely satisfactory estimation of MC and PC cell responses to complex waveforms. As a consequence of their transient responses, MC responses to complex waveforms were found to have significantly more energy in higher spatial harmonic components than PC responses. Response variance (noise) was also quantified as a function of harmonic component. Noise increased to some degree for the higher harmonics. The data are relevant for psychophysical detection or discrimination of visual patterns, and we discuss the results in this context.
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Semenova, Svetlana B., Irina O. Vassilieva, Alla F. Fomina, Andrey L. Runov, and Yuri A. Negulyaev. "Endogenous expression of TRPV5 and TRPV6 calcium channels in human leukemia K562 cells." American Journal of Physiology-Cell Physiology 296, no. 5 (May 2009): C1098—C1104. http://dx.doi.org/10.1152/ajpcell.00435.2008.
Full textAbstract:
In blood cells, changes in intracellular Ca2+ concentration ([Ca2+]i) are associated with multiple cellular events, including activation of cellular kinases and phosphatases, degranulation, regulation of cytoskeleton binding proteins, transcriptional control, and modulation of surface receptors. Although there is no doubt as to the significance of Ca2+ signaling in blood cells, there is sparse knowledge about the molecular identities of the plasmalemmal Ca2+ permeable channels that control Ca2+ fluxes across the plasma membrane and mediate changes in [Ca2+]i in blood cells. Using RNA expression analysis, we have shown that human leukemia K562 cells endogenously coexpress transient receptor potential vanilloid channels type 5 (TRPV5) and type 6 (TRPV6) mRNAs. Moreover, we demonstrated that TRPV5 and TRPV6 channel proteins are present in both the total lysates and the crude membrane preparations from leukemia cells. Immunoprecipitation revealed that a physical interaction between TRPV5 and TRPV6 may take place. Single-channel patch-clamp experiments demonstrated the presence of inwardly rectifying monovalent currents that displayed kinetic characteristics of unitary TRPV5 and/or TRPV6 currents and were blocked by extracellular Ca2+ and ruthenium red. Taken together, our data strongly indicate that human myeloid leukemia cells coexpress functional TRPV5 and TRPV6 calcium channels that may interact with each other and contribute into intracellular Ca2+ signaling.
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Nakamura, Tomoe Y., Michael Artman, Bernardo Rudy, and William A. Coetzee. "Inhibition of rat ventricularI K1 with antisense oligonucleotides targeted to Kir2.1 mRNA." American Journal of Physiology-Heart and Circulatory Physiology 274, no. 3 (March 1, 1998): H892—H900. http://dx.doi.org/10.1152/ajpheart.1998.274.3.h892.
Full textAbstract:
The cardiac inward rectifying K+ current ( I K1) is important in maintaining the maximum diastolic potential. We used antisense oligonucleotides to determine the role of Kir2.1 channel proteins in the genesis of native rat ventricular I K1. A combination of two antisense phosphorothioate oligonucleotides inhibited heterologously expressed Kir2.1 currents in Xenopus oocytes, either when coinjected with Kir2.1 cRNA or when applied in the incubation medium. Specificity was demonstrated by the lack of inhibition of Kir2.2 and Kir2.3 currents in oocytes. In rat ventricular myocytes (4–5 days culture), these oligonucleotides caused a significant reduction of whole cell I K1(without reducing the transient outward K+ current or the L-type Ca2+ current). Cell-attached patches demonstrated the occurrence of multiple channel events in control myocytes (8, 14, 21, 35, 43, and 80 pS). The 21-pS channel was specifically knocked down in antisense-treated myocytes (fewer patches contained this channel, and its open frequency was reduced). These results demonstrate that the Kir2.1 gene encodes a specific native 21-pS K+-channel protein and that this channel has an essential role in the genesis of cardiac I K1.
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Bordey, Angélique, and Harald Sontheimer. "Electrophysiological Properties of Human Astrocytic Tumor Cells In Situ: Enigma of Spiking Glial Cells." Journal of Neurophysiology 79, no. 5 (May 1, 1998): 2782–93. http://dx.doi.org/10.1152/jn.1998.79.5.2782.
Full textAbstract:
Bordey, Angélique and Harald Sontheimer. Electrophysiological properties of human astrocytic tumor cells in situ: enigma of spiking glial cells. J. Neurophysiol. 79: 2782–2793, 1998. To better understand physiological changes that accompany the neoplastic transition of astrocytes to become astrocytoma cells, we studied biopsies of low-grade, pilocytic astrocytomas. This group of tumors is most prevalent in children and the tumor cells maintain most antigenic features typical of astrocytes. Astrocytoma cells were studied with the use of whole cell patch-clamp recordings in acute biopsy slices from 4-mo- to 14-yr-old pediatric patients. Recordings from 53 cells in six cases of low-grade astrocytomas were compared to either noncancerous peritumoral astrocytes or astrocytes obtained from other surgeries. Astrocytoma cells almost exclusively displayed slowly activating, sustained, tetraethylammonium (TEA)-sensitive outward potassium currents (delayed rectifying potassium currents; I DR) and transient, tetrodotoxin (TTX)-sensitive sodium currents ( I Na). By contrast, comparison glial cells from peritumoral regions or other surgeries showed I DR and I Na, but in addition these cells also expressed transient “A”-type K+ currents and inwardly rectifying K+ currents ( I IR), both of which were absent in astrocytoma cells. I IR constituted the predominant conductance in comparison astrocytes and was responsible for a high-resting K+ conductance in these cells. Voltage-activated Na+ currents were observed in 37 of 53 astrocytoma cells. Na+ current densities in astrocytoma cells, on average, were three- to fivefold larger than in comparison astrocytes. Astrocytoma cells expressing I Na could be induced to generate slow action potential-like responses (spikes) by current injections. The threshold for generating such spikes was −34 mV (from a holding potential of −70 mV). The spike amplitude and time width were 52.5 mV and 12 ms, respectively. No spikes could be elicited in comparison astrocytes, although some of them expressed Na+ currents of similar size. Comparison of astrocytes to astrocytoma cells suggests that the apparent lack of I IR, which leads to high-input resistance (>500 MΩ), allows glioma cells to be sufficiently depolarized to generate Na+ spikes, whereas the high resting K+ conductance in astrocytes prevents their depolarization and thus generation of spikes. Consistent with this notion, Na+ spikes could be induced in spinal cord astrocytes in culture when I IR was experimentally blocked by 10 μM Ba2+, suggesting that the absence of I IR in astrocytoma cells is primarily responsible for the unusual spiking behavior seen in these glial tumor cells. It is unlikely that such glial spikes ever occur in vivo.
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Bordey, Angélique, and Harald Sontheimer. "Postnatal Development of Ionic Currents in Rat Hippocampal Astrocytes In Situ." Journal of Neurophysiology 78, no. 1 (July 1, 1997): 461–77. http://dx.doi.org/10.1152/jn.1997.78.1.461.
Full textAbstract:
Bordey, Angélique and Harald Sontheimer. Postnatal development of ionic currents in rat hippocampal astrocytes in situ. J. Neurophysiol. 78: 461–477, 1997. Developmental changes in ion channel expression and cell morphology were studied in glial cells with the use of whole cell patch-clamp recordings in rat [postnatal day (P)5–P50] hippocampal slices. Recordings were obtained from 234 cells, presumed to be glia, in stratum radiatum and stratum lacunosum-moleculare of the CA1 region. Of 66 recorded cells filled with Lucifer yellow, 48 stained positive for glial fibrillary acidic protein, which identified them as astrocytes. All glial cells studied were of a stellate morphology, and developmental changes primarily comprised an increase in the length and number of cell processes associated with an overall increase in cell size and membrane capacitance. Two distinct outward potassium currents could be identified: a transient 4-aminopyridine-sensitive current ( I a) and a persistent outward current sensitive to tetraethylammonium ( I d). I a activated at −40 mV, and steady-state activation and inactivation midpoints were −16 and −74 mV, respectively. Decay time constants ranged from 7 ms at −30 mV to 19 ms at +80 mV. I d activated at −30 mV. A third K+ current sensitive to cesium activated with hyperpolarizing command voltages and showed strong inward rectification. Transient, voltage-activated sodium currents ( I Na) were tetrodotoxin sensitive (100 nM) and activated at about −40 mV, peaked at about −10 mV, and reversed at +63 mV. I Na was half-inactivated at −49 mV and half-activated at −19 mV. During the first 2 wk of postnatal development, the percentage of cells showing inwardly rectifying K+ current ( I r), I a, and I Na increased significantly from 40% (at P5) to 90% (at P20–P50). By contrast, almost all cells independent of age expressed I d. Specific conductances for I r ( g ir) and I a increased significantly between P5 and P20, concomitant with a decrease in input resistance. By contrast, specific conductance of the outwardly rectifying K+ current ( g d) decreased threefold between P5 and P20. Specific Na+ conductance was always <1/4 of the total potassium conductance. These results indicate that CA1 hippocampal astrocytes are characterized by expression of voltage-activated Na+ channels and three types of K+ channels showing changes in their relative expression during early postnatal development: 1) the number of cells expressing I a, I r, and I Na increases significantly and 2) their specific conductance changes such that g d, predominant at P5–P20, is gradually replaced by g ir, the predominant conductance in adult astrocytes. Adult morphological and electrophysiological phenotypes are established at about P20. These data suggest that previous studies in which cultured or acutely isolated cells from immature or embryonic rats were used were not adequately reflecting the properties of hippocampal astrocytes in situ.
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Oginsky, Max F., and Carrie R. Ferrario. "Eating “junk food” has opposite effects on intrinsic excitability of nucleus accumbens core neurons in obesity-susceptible versus -resistant rats." Journal of Neurophysiology 122, no. 3 (September 1, 2019): 1264–73. http://dx.doi.org/10.1152/jn.00361.2019.
Full textAbstract:
The nucleus accumbens (NAc) plays critical roles in motivated behaviors, including food seeking and feeding. Differences in NAc function contribute to overeating that drives obesity, but the underlying mechanisms are poorly understood. In addition, there is a fair degree of variation in individual susceptibility versus resistance to obesity that is due in part to differences in NAc function. For example, using selectively bred obesity-prone and obesity-resistant rats, we have found that excitability of medium spiny neurons (MSNs) within the NAc core is enhanced in obesity-prone versus -resistant populations, before any diet manipulation. However, it is unknown whether consumption of sugary, fatty “junk food” alters MSN excitability. Here whole cell patch-clamp recordings were conducted to examine MSN intrinsic excitability in adult male obesity-prone and obesity-resistant rats with and without exposure to a sugary, fatty junk food diet. We replicated our initial finding that basal excitability is enhanced in obesity-prone versus obesity-resistant rats and determined that this is due to a lower fast transient potassium current ( IA) in prone versus resistant groups. In addition, the junk food diet had opposite effects on excitability in obesity-prone versus obesity-resistant rats. Specifically, junk food enhanced excitability in MSNs of obesity-resistant rats; this was mediated by a reduction in IA. In contrast, junk food reduced excitability in MSNs from obesity-prone rats; this was mediated by an increase in inward-rectifying potassium current. Thus individual differences in obesity susceptibility influence both basal excitability and how MSN excitability adapts to junk food consumption. NEW & NOTEWORTHY Medium spiny neurons (MSNs) in the nucleus accumbens of obesity-prone rats are hyperexcitable compared with MSNs from obesity-resistant rats. We found that 10 days of “junk food” exposure reduces MSN excitability in obesity-prone rats by increasing inward-rectifying potassium current and increases MSN excitability in obesity-resistant rats by decreasing fast transient potassium current. These data show that there are basal and junk food diet-induced differences in MSN excitability in obesity-prone and obesity-resistant individuals; this may contribute to previously observed differences in incentive motivation.
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Leblanc, N., and P. M. Leung. "Indirect stimulation of Ca(2+)-activated Cl- current by Na+/Ca2+ exchange in rabbit portal vein smooth muscle." American Journal of Physiology-Heart and Circulatory Physiology 268, no. 5 (May 1, 1995): H1906—H1917. http://dx.doi.org/10.1152/ajpheart.1995.268.5.h1906.
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Macroscopic currents were recorded in freshly dissociated smooth muscle cells from the rabbit portal vein using the tight seal whole cell recording mode (22 degrees C). In some experiments, the indo 1 fluorescence technique was used to simultaneously monitor the changes in the concentration of free intracellular Ca2+ ([Ca2+]i; indo 1 ratio, 400/500 nm). In cells exposed to tetraethylammonium chloride (TEA) to inhibit K+ channels and 1-10 microM nifedipine or nicardipine to inhibit L-type Ca2+ channels, cell dialysis with 30 mM Na+ increased [Ca2+]i and induced membrane current consistent with the activation of Ca(2+)-activated Cl- channels [ICl(Ca)]. From holding potential (HP) of -60 mV, high intracellular Na+ concentration ([Na+]i)-mediated current was instantaneous in response to 0.5- to 10-s voltage clamp pulses from -80 to +20 mV; steps ranging from +20 to +80 mV evoked slow time-dependent outward current (I(t); superimposed on the instantaneous current) and voltage-dependent Ca2+ transient; on return to HP, slow inward tail current appeared that reflected deactivation of I(t). Both current components 1) exhibited outward rectifying properties, 2) reversed near the predicted equilibrium potential for Cl-, 3) were stimulated by elevation of extracellular Ca2+ concentration, 4) were abolished when the cells were dialyzed with 5 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, and 5) were inhibited by extracellular application of niflumic acid (50 microM). Complete replacement of extracellular Na+ concentration with tetramethylammonium increased both the instantaneous and time-dependent components of ICl(Ca), resting [Ca2+]i at -60 mV and Ca2+ transient at +40 mV. Cell dialysis with Na(+)-free pipette solution prevented these effects. Our results are consistent with an indirect mechanism of stimulation of ICl(Ca), which involves intracellular Ca2+ accumulation via reverse-mode electrogenic Na+/Ca2+ exchange activity.
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Adorante, Joseph S., and Jeffrey L. Edelman. "Letters to the Editor." American Journal of Physiology-Cell Physiology 273, no. 4 (October 1, 1997): C1435—C1436. http://dx.doi.org/10.1152/ajpcell.1997.273.4.c1435.
Full textAbstract:
The following is the abstract of the article discussed in the subsequent letter: Mitchell, Claire H., Jin Jun Zhang, Liwei Wang, and Tim J. C. Jacob. Volume-sensitive chloride current in pigmented ciliary epithelial cells: role of phospholipases. Am. J. Physiol. 272 ( Cell Physiol. 41): C212–C222, 1997.—The whole cell recording technique was used to examine an outwardly rectifying chloride current activated by hypotonic shock in bovine pigmented ciliary epithelial (PCE) cells. Removal of internal and external Ca2+ did not affect the activation of these currents, but they were abolished by the phospholipase C inhibitor neomycin. The current was blocked by 5-nitro-2-(3-phenylpropylamino)benzoic acid, 4-acetamido-4′-isothiocyanostilbene-2,2′-disulfonic acid, and 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) in a voltage-dependent manner, but tamoxifen, dideoxyforskolin, and quinidine did not affect it. This blocking profile differs from that of the volume-sensitive chloride channel in neighboring nonpigmented ciliary epithelial cells (Wu, J., J. J. Zhang, H. Koppel, and T. J. C. Jacob. J. Physiol. Lond. 491: 743–755, 1996), and this difference implies that the volume responses of the two cell types are mediated by different chloride channels (Jacob, T. J. C., and J. J. Zhang. J. Physiol. Lond. In press). Intracellular administration of guanosine 5′- O-(3-thiotriphosphate) (GTPγS) to PCE cells induced a transient, time-independent, outwardly rectifying chloride current that closely resembled the current activated by hypotonic shock. DIDS produced a voltage-dependent block of the GTPγS-activated current similar to the block of the hypotonically activated current. Intracellular neomycin completely prevented activation of this current as did incubation of the cells in calphostin C, an inhibitor of protein kinase C (PKC). Removal of Ca2+ did not affect activation of the current by GTPγS but extended the duration of the response. Inhibition of phospholipase A2 (PLA2) with p-bromophenacyl bromide prevented the activation of the hypotonically induced current and also inhibited the current once activated by hypotonic solution. The findings imply that the hypotonic response in PCE cells is mediated by both phospholipase C (PLC) and PLA2. Both phospholipases generate arachidonic acid, and, in addition, the PLC pathway regulates the PLA2 pathway via a PKC-dependent phosphorylation of PLA2.
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Vassort, Guy. "Adenosine 5′-Triphosphate: a P2-Purinergic Agonist in the Myocardium." Physiological Reviews 81, no. 2 (April 1, 2001): 767–806. http://dx.doi.org/10.1152/physrev.2001.81.2.767.
Full textAbstract:
ATP, besides an intracellular energy source, is an agonist when applied to a variety of different cells including cardiomyocytes. Sources of ATP in the extracellular milieu are multiple. Extracellular ATP is rapidly degraded by ectonucleotidases. Today ionotropic P2X1–7receptors and metabotropic P2Y1,2,4,6,11receptors have been cloned and their mRNA found in cardiomyocytes. On a single cardiomyocyte, micromolar ATP induces nonspecific cationic and Cl−currents that depolarize the cells. ATP both increases directly via a Gsprotein and decreases Ca2+current. ATP activates the inward-rectifying currents (ACh- and ATP-activated K+currents) and outward K+currents. P2-purinergic stimulation increases cAMP by activating adenylyl cyclase isoform V. It also involves tyrosine kinases to activate phospholipase C-γ to produce inositol 1,4,5-trisphosphate and Cl−/HCO[Formula: see text] exchange to induce a large transient acidosis. No clear correlation is presently possible between an effect and the activation of a given P2-receptor subtype in cardiomyocytes. ATP itself is generally a positive inotropic agent. Upon rapid application to cells, ATP induces various forms of arrhythmia. At the tissue level, arrhythmia could be due to slowing of electrical spread after both Na+current decrease and cell-to-cell uncoupling as well as cell depolarization and Ca2+current increase. In as much as the information is available, this review also reports analog effects of UTP and diadenosine polyphosphates.
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Yarishkin, Oleg, Tam T. T. Phuong, Colin A. Bretz, Kenneth W. Olsen, Jackson M. Baumann, Monika Lakk, Alan Crandall, Catherine Heurteaux, Mary E. Hartnett, and David Križaj. "TREK-1 channels regulate pressure sensitivity and calcium signaling in trabecular meshwork cells." Journal of General Physiology 150, no. 12 (November 16, 2018): 1660–75. http://dx.doi.org/10.1085/jgp.201812179.
Full textAbstract:
Mechanotransduction by the trabecular meshwork (TM) is an essential component of intraocular pressure regulation in the vertebrate eye. This process is compromised in glaucoma but is poorly understood. In this study, we identify transient receptor potential vanilloid isoform 4 (TRPV4) and TWIK-related potassium channel-1 (TREK-1) as key molecular determinants of TM membrane potential, pressure sensitivity, calcium homeostasis, and transcellular permeability. We show that resting membrane potential in human TM cells is unaffected by “classical” inhibitors of voltage-activated, calcium-activated, and inwardly rectifying potassium channels but is depolarized by blockers of tandem-pore K+ channels. Using gene profiling, we reveal the presence of TREK-1, TASK-1, TWIK-2, and THIK transcripts in TM cells. Pressure stimuli, arachidonic acid, and TREK-1 activators hyperpolarize these cells, effects that are antagonized by quinine, amlodipine, spadin, and short-hairpin RNA–mediated knockdown of TREK-1 but not TASK-1. Activation and inhibition of TREK-1 modulates [Ca2+]TM and lowers the impedance of cell monolayers. Together, these results suggest that tensile homeostasis in the TM may be regulated by balanced, pressure-dependent activation of TRPV4 and TREK-1 mechanotransducers.
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Hollins, Bettye, and Stephen R. Ikeda. "Heterologous Expression of a P2 x-Purinoceptor in Rat Chromaffin Cells Detects Vesicular ATP Release." Journal of Neurophysiology 78, no. 6 (December 1, 1997): 3069–76. http://dx.doi.org/10.1152/jn.1997.78.6.3069.
Full textAbstract:
Hollins, Bettye and Stephen R. Ikeda. Heterologous expression of a P2 x -purinoceptor in rat chromaffin cells detects vesicular ATP release. J. Neurophysiol. 78: 3069–3076, 1997. A cloned P2 x -purinoceptor was transiently expressed in single isolated rat adrenal chromaffin cells and evaluated for the detection of released ATP. After cytoplasmic injection of the P2 x complementary RNA (cRNA; 4–24 h), application of ATP produced an inwardly rectifying current over the voltage range −130 to −10 mV as measured by the whole cell patch-clamp technique. The dose-response curve for ATP was sigmoidal with a 50% effective concentration of 18.2 μM. Suramin, a P2 x -antagonist, attenuated the ATP-induced current. Depolarizing voltage pulses to 0 mV or application of histamine, stimuli that trigger exocytosis, resulted in the appearance of suramin-sensitive spontaneous transient inward currents (at −60 mV) that resembled excitatory postsynaptic currents although they were slower in time course. Concurrent detection of catecholamine release with a carbon fiber electrode often showed coincidence of the amperometric current with the synaptic currentlike events suggesting that ATP and catecholamines were released from the same vessicle. These data demonstrate that expression of a P2 x -purinoceptor in chromaffin cells produces a functional autoreceptor capable of detecting vesicular release of ATP. In combination with carbon fiber amperometry, simultaneous vesicular release of two neurotransmitters from a single chromaffin cell could be monitored. The P2 x -purinoceptor, however, produced a regenerative effect on release apparently resulting from the high Ca2+ permeability of the receptor. Thus modification of the P2 x -purinoceptor would be required before the system could be applied to examining processes involved in stimulus-release coupling.
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Kinnamon, S. C., and S. D. Roper. "Membrane properties of isolated mudpuppy taste cells." Journal of General Physiology 91, no. 3 (March 1, 1988): 351–71. http://dx.doi.org/10.1085/jgp.91.3.351.
Full textAbstract:
The voltage-dependent currents of isolated Necturus lingual cells were studied using the whole-cell configuration of the patch-clamp technique. Nongustatory surface epithelial cells had only passive membrane properties. Small, spherical cells resembling basal cells responded to depolarizing voltage steps with predominantly outward K+ currents. Taste receptor cells generated both outward and inward currents in response to depolarizing voltage steps. Outward K+ currents activated at approximately 0 mV and increased almost linearly with increasing depolarization. The K+ current did not inactivate and was partially Ca++ dependent. One inward current activated at -40 mV, reached a peak at -20 mV, and rapidly inactivated. This transient inward current was blocked by tetrodotoxin (TTX), which indicates that it is an Na+ current. The other inward current activated at 0 mV, peaked at 30 mV, and slowly inactivated. This more sustained inward current had the kinetic and pharmacological properties of a slow Ca++ current. In addition, most taste cells had inwardly rectifying K+ currents. Sour taste stimuli (weak acids) decreased outward K+ currents and slightly reduced inward currents; bitter taste stimuli (quinine) reduced inward currents to a greater extent than outward currents. It is concluded that sour and bitter taste stimuli produce depolarizing receptor potentials, at least in part, by reducing the voltage-dependent K+ conductance.
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Zhang, H., A. V. Holden, I. Kodama, H. Honjo, M. Lei, T. Varghese, and M. R. Boyett. "Mathematical models of action potentials in the periphery and center of the rabbit sinoatrial node." American Journal of Physiology-Heart and Circulatory Physiology 279, no. 1 (July 1, 2000): H397—H421. http://dx.doi.org/10.1152/ajpheart.2000.279.1.h397.
Full textAbstract:
Mathematical models of the action potential in the periphery and center of the rabbit sinoatrial (SA) node have been developed on the basis of published experimental data. Simulated action potentials are consistent with those recorded experimentally: the model-generated peripheral action potential has a more negative takeoff potential, faster upstroke, more positive peak value, prominent phase 1 repolarization, greater amplitude, shorter duration, and more negative maximum diastolic potential than the model-generated central action potential. In addition, the model peripheral cell shows faster pacemaking. The models behave qualitatively the same as tissue from the periphery and center of the SA node in response to block of tetrodotoxin-sensitive Na+current, L- and T-type Ca2+ currents, 4-aminopyridine-sensitive transient outward current, rapid and slow delayed rectifying K+ currents, and hyperpolarization-activated current. A one-dimensional model of a string of SA node tissue, incorporating regional heterogeneity, coupled to a string of atrial tissue has been constructed to simulate the behavior of the intact SA node. In the one-dimensional model, the spontaneous action potential initiated in the center propagates to the periphery at ∼0.06 m/s and then into the atrial muscle at 0.62 m/s.
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Li, Gui-Rong, Jianlin Feng, Lixia Yue, and Michel Carrier. "Transmural heterogeneity of action potentials andI to1 in myocytes isolated from the human right ventricle." American Journal of Physiology-Heart and Circulatory Physiology 275, no. 2 (August 1, 1998): H369—H377. http://dx.doi.org/10.1152/ajpheart.1998.275.2.h369.
Full textAbstract:
Limited information is available about transmural heterogeneity in cardiac electrophysiology in man. The present study was designed to evaluate heterogeneity of cardiac action potential (AP), transient outward K+ current ( I to1) and inwardly rectifying K+ current ( I K1) in human right ventricle. AP and membrane currents were recorded using whole cell current- and voltage-clamp techniques in myocytes isolated from subepicardial, midmyocardial, and subendocardial layers of the right ventricle of explanted failing human hearts. AP morphology differed among the regional cell types. AP duration (APD) at 0.5–2 Hz was longer in midmyocardial cells (M cells) than in subepicardial and subendocardial cells. At room temperature, observed I to1, on step to +60 mV, was significantly greater in subepicardial (6.9 ± 0.8 pA/pF) and M cells (6.0 ± 1.1 pA/pF) than in subendocardial cells (2.2 ± 0.7 pA/pF, P < 0.01). Slower recovery of I to1 was observed in subendocardial cells. The half-inactivation voltage of I to1 was more negative in subendocardial cells than in M and subepicardial cells. At 36°C, the density of I to1 increased, the time-dependent inactivation and reactivation accelerated, and the frequency-dependent reduction attenuated in all regional cell types. No significant difference was observed in I K1 density among the regional cell types. The results indicate that M cells in humans, as in canines, show the greatest APD and that a gradient of I to1 density is present in the transmural ventricular wall. Therefore, the human right ventricle shows significant transmural heterogeneity in AP morphology and I to1properties.
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Oberwinkler, Johannes, Annette Lis, Klaus M. Giehl, Veit Flockerzi, and Stephan E. Philipp. "Alternative Splicing Switches the Divalent Cation Selectivity of TRPM3 Channels." Journal of Biological Chemistry 280, no. 23 (April 11, 2005): 22540–48. http://dx.doi.org/10.1074/jbc.m503092200.
Full textAbstract:
TRPM3 is a poorly understood member of the large family of transient receptor potential (TRP) ion channels. Here we describe five novel splice variants of TRPM3, TRPM3α1–5. These variants are characterized by a previously unknown amino terminus of 61 residues. The differences between the five variants arise through splice events at three different sites. One of these splice sites might be located in the pore region of the channel as indicated by sequence alignment with other, better-characterized TRP channels. We selected two splice variants, TRPM3α1 and TRPM3α2, that differ only in this presumed pore region and analyzed their biophysical characteristics after heterologous expression in human embryonic kidney 293 cells. TRPM3α1 as well as TRPM3α2 induced a novel, outwardly rectifying cationic conductance that was tightly regulated by intracellular Mg2+. However, these two variants are highly different in their ionic selectivity. Whereas TRPM3α1-encoded channels are poorly permeable for divalent cations, TRPM3α2-encoded channels are well permeated by Ca2+ and Mg2+. Additionally, we found that currents through TRPM3α2 are blocked by extracellular monovalent cations, whereas currents through TRPM3α1 are not. These differences unambiguously show that TRPM3 proteins constitute a pore-forming channel subunit and localize the position of the ion-conducting pore within the TRPM3 protein. Although the ionic selectivity of ion channels has traditionally been regarded as rather constant for a given channel-encoding gene, our results show that alternative splicing can be a mechanism to produce channels with very different selectivity profiles.
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Yin, Ming Zhe, Hae Jin Kim, Eun Yeong Suh, Yin Hua Zhang, Hae Young Yoo, and Sung Joon Kim. "Endurance exercise training restores atrophy-induced decreases of myogenic response and ionic currents in rat skeletal muscle artery." Journal of Applied Physiology 126, no. 6 (June 1, 2019): 1713–24. http://dx.doi.org/10.1152/japplphysiol.00962.2018.
Full textAbstract:
Atrophic limbs exhibit decreased blood flow and histological changes in the arteries perfusing muscles. However, the effect of atrophy on vascular smooth muscle function is poorly understood. Here, we investigated the effect of unilateral sciatic denervation on the myogenic response (MR) and the ionic currents in deep femoral artery (DFA) smooth muscles from Sprague-Dawley rats. Because denervated rats were capable of treadmill exercise (20 m/min, 30 min, 3 times/wk), the impact of exercise training on these effects was also assessed. Skeletal arteries were harvested 3 or 5 wk after surgery. Then skeletal arteries or myocytes were subjected to video analysis of pressurized artery, myography, whole-cell patch clamp, and real-time quantitative PCR to determine the effect of hindlimb paralysis in the presence/absence of exercise training on MR, contractility, ionic currents, and channel transcription, respectively. In sedentary rats, atrophy was associated with loss of MR in the DFA at 5 wk. The contralateral DFA had a normal MR. At 5 wk after surgery, DFA myocytes from the atrophic limbs exhibited depressed L-type Ca2+currents, GTPγS-induced transient receptor potential cation channel (TRPC)-like currents, 80 mM KCl-induced vasoconstriction, TRPC6 mRNA, and voltage-gated K+and inwardly rectifying K+currents. Exercise training abrogated the differences in all of these functions between atrophic side and contralateral side DFA myocytes. These results suggest that a probable increase in hemodynamic stimuli in skeletal artery smooth muscle plays an important role in maintaining MR and ionic currents in skeletal artery smooth muscle. This may also explain the observed benefits of exercise in patients with limb paralysis.NEW & NOTEWORTHY Myogenic responses (MRs) in rat skeletal arteries feeding the unilateral atrophic hindlimb were impaired. In addition, the L-type Ca2+channel current, the TRPC6-like current, and TRPC6 mRNA levels in the corresponding myocytes decreased. Voltage-gated K+channel currents and inwardly rectifying K+channel currents were also attenuated in atrophic side myocytes. Exercise training effectively abrogated electrophysiological dysfunction of atrophic side myocytes and prevented loss of the MR.
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Shimoni, Y., and H. Banno. "Thyroxine effects on temperature dependence of ionic currents in single rabbit cardiac myocytes." American Journal of Physiology-Heart and Circulatory Physiology 265, no. 6 (December 1, 1993): H1875—H1883. http://dx.doi.org/10.1152/ajpheart.1993.265.6.h1875.
Full textAbstract:
Macroscopic whole cell currents were measured from single rabbit cardiac myocytes, using the suction electrode voltage-clamp technique, under euthyroid, hyperthyroid, and hypothyroid conditions. In ventricular myocytes, the temperature dependence of the transient outward current (I(t)) was greatly reduced in hyperthyroid conditions, with Q10 values (between 22 and 32 degrees C) reduced from normal values of 6.14 +/- 0.93 (SE, n = 8) to 2.14 +/- 0.14 (n = 6). In contrast, two of the other major currents in these cells were relatively unaffected. Under hyperthyroid conditions, there was very little change in the amplitudes or temperature dependence of L-type calcium currents and of steady-state currents, which reflect mainly the inwardly rectifying potassium current. In atrial cells no changes in the temperature dependence of I(t) were observed, with virtually identical Q10 values (close to 4) in eu- and hyperthyroid conditions. Under hypothyroid conditions, there was no change in the temperature dependence of I(t) in either ventricular or atrial cells. We conclude that the regulation of I(t) in ventricular cells is unique, rendering it extremely sensitive to temperature changes and to elevations in thyroxine levels. These results are discussed in the context of long-term regulation of ionic channels.
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Bychkov, R., J. Glowinski, and C. Giaume. "Sequential and opposite regulation of two outward K+ currents by ET-1 in cultured striatal astrocytes." American Journal of Physiology-Cell Physiology 281, no. 4 (October 1, 2001): C1373—C1384. http://dx.doi.org/10.1152/ajpcell.2001.281.4.c1373.
Full textAbstract:
In the brain, astrocytes represent a major target for endothelins (ETs), a family of peptides that can be released by several cell types and that have potent and multiple effects on astrocytic functions. Four types of K+ currents ( I K) were detected in various proportions by patch-clamp recordings of cultured striatal astrocytes, including the A-type I K, the inwardly rectifying I K IR, the Ca2+-dependent I K( I K Ca), and the delayed-rectified I K ( I K DR). Variations in the shape of current-voltage relationships were related mainly to differences in the proportion of these currents. ET-1 was found to regulate with opposite effects the two more frequently recorded outward K+ currents in striatal astrocytes. Indeed, this peptide induced an initial activation of I K Ca(composed of SK and BK channels) and a delayed long-lasting inhibition of I K DR. In current-clamp recordings, the activation of I K Ca correlated with a transient hyperpolarization, whereas the inhibition of I K DR correlated with a sustained depolarization. These ET-1-induced sequential changes in membrane potential in astrocytes may be important for the regulation of voltage gradients in astrocytic networks and the maintenance of K+ homeostasis in the brain microenvironment.
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Strohmann, B., D. W. Schwarz, and E. Puil. "Mode of firing and rectifying properties of nucleus ovoidalis neurons in the avian auditory thalamus." Journal of Neurophysiology 71, no. 4 (April 1, 1994): 1351–60. http://dx.doi.org/10.1152/jn.1994.71.4.1351.
Full textAbstract:
1. We studied neurons of the nucleus ovoidalis, the principal auditory thalamic relay nucleus of the chicken, with tight-seal whole-cell recording techniques in in vitro slice preparations. Nucleus ovoidalis, marked by anterograde labeling of afferents from the inferior colliculus, consists of a clearly delineated group of densely packed, multipolar cells of approximately uniform diameter. We measured a wide range of non covarying resting potentials (-60 +/- 9 mV, mean +/- SD) and input resistances (277 +/- 168 M omega). All neurons discharged overshooting fast spikes. The observed electrophysiological properties may have a decisive role in the transfer of sensory signals. 2. We grouped neurons on the basis of their firing patterns, in response to intracellular injections of depolarizing current pulses from various membrane potentials. The majority of neurons (86%) displayed weakly adapting, tonic firing. A smaller group of neurons (14%) exhibited qualitative changes in firing modes. They fired repetitively when the stimulus pulse was superimposed on relatively depolarized levels, usually including the resting potential. DC-hyperpolarization led to burst responses consisting of fast action potentials on top of slow potentials. 3. In all neurons, application of 300 nM tetrodotoxin blocked the action potentials and reduced a depolarization-activated inward rectification, observed during 1-s current pulses in a range of membrane potentials depolarized from rest. This rectification is interpreted as a partial result of a persistent Na+ current. 4. During the applications of tetrodotoxin in neurons with burst firing capability, two other slow potentials were visible in isolation. Depolarizing current pulses evoked slow, transient depolarizations at the onset whereas rebound slow potentials occurred on termination of hyperpolarizing current pulses. The slow potentials were blocked by application of 0.5 mM Ni2+ and are likely a result of a low threshold Ca2+ current, such as a T-current. 5. A distinctive property of all ovoidalis neurons was a hyperpolarization-activated inward rectification. Application of Cs+ (3 mM) but not Ba2+ (3 mM), tetraethylammonium (10 mM), or 4-aminopyridine (4 mM) reversibly blocked the current that produced this rectification. The activation time constants for the current varied between approximately 50 and 400 ms and were voltage dependent in some neurons. Thus the hyperpolarization-activated current (IH), responsible for thalamic sleep mechanisms in mammals, also is present in a submammalian thalamus. 6. We suggest that the voltage and time dependencies of the persistent Na+ current and IH participate in generation of the sub- and suprathreshold temporal activity patterns in the neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
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Santarius, Megan, Chang Ho Lee, and Richard A. Anderson. "Supervised membrane swimming: small G-protein lifeguards regulate PIPK signalling and monitor intracellular PtdIns(4,5)P2 pools." Biochemical Journal 398, no. 1 (July 27, 2006): 1–13. http://dx.doi.org/10.1042/bj20060565.
Full textAbstract:
Regulation of PIPK (phosphatidylinositol phosphate kinase) and PtdIns(4,5)P2 signalling by small G-proteins and their effectors is key to many biological functions. Through selective recruitment and activation of different PIPK isoforms, small G-proteins such as Rho, Rac and Cdc42 modulate actin dynamics and cytoskeleton-dependent cellular events in response to extracellular signalling. These activities affect a number of processes, including endocytosis, bacterial penetration into host cells and cytolytic granule-mediated targeted cell killing. Small G-proteins and their modulators are also regulated by phosphoinositides through translocation and conformational changes. Arf family small G-proteins act at multiple sites as regulators of membrane trafficking and actin cytoskeletal remodelling, and regulate a feedback loop comprising phospholipase D, phosphatidic acid, PIPKs and PtdIns(4,5)P2, contributing to enhancement of PtdIns(4,5)P2-mediated cellular events and receptor signalling. Na+, Kir (inwardly rectifying K+), Ca2+ and TRP (transient receptor potential) ion channels are regulated by small G-proteins and membrane pools of PtdIns(4,5)P2. Yeast phosphatidylinositol 4-phosphate 5-kinases Mss4 and Its3 are involved in resistance against disturbance of sphingolipid biosynthesis and maintenance of cell integrity through the synthesis of PtdIns(4,5)P2 and downstream signalling through the Rom2/Rho2 and Rgf1/Rho pathways. Here, we review models for regulated intracellular targeting of PIPKs by small G-proteins and other modulators in response to extracellular signalling. We also describe the spatial and temporal cross-regulation of PIPKs and small G-proteins that is critical for a number of cellular functions.
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Grolleau, F., and B. Lapied. "Separation and identification of multiple potassium currents regulating the pacemaker activity of insect neurosecretory cells (DUM neurons)." Journal of Neurophysiology 73, no. 1 (January 1, 1995): 160–71. http://dx.doi.org/10.1152/jn.1995.73.1.160.
Full textAbstract:
1. Whole cell voltage-clamp studies performed in isolated adult neurosecretory cells identified as dorsal unpaired median (DUM) neurons of the terminal abdominal ganglion of the cockroach Periplaneta americana have allowed us to reveal a complex voltage-dependent outward current regulating the pacemaker activity. 2. The global outward current remaining after tetrodotoxin treatment was activated by depolarization above -50 mV, showing steep voltage dependence and outward rectification. 3. We used tail current analysis to determine the ionic selectivity of this outward current. The reversal potentials for two extracellular potassium concentrations (-92.7 and -65.4 mV for 3.1 and 10 mM, respectively) is consistent with the expected equilibrium potential for potassium ions. 4. Both peak and sustained components of the global outward K+ current were reduced by external application of 20 mM tetraethylammonium chloride, 10 nM iberiotoxin, 1 nM charybdotoxin (CTX) and 1 mM cadmium chloride. Subtraction of current recorded in CTX solution from that in control solution revealed an unusual biphasic Ca(2+)-dependent K+ current. The fast transient current resistant to 5 mM 4-aminopyridine (4-AP) is distinguished by its dependence on holding potential and time course from the late sustained current. 5. In addition, two other components of CTX-resistant outward K+ current could be separated by sensitivity to 4-AP, time course, and voltage dependence. Beside a calcium-independent delayed outwardly rectifying current, a 4-AP-sensitive fast transient current resembling the A-current has been also identified. It activates at negative potential (about -65 mV) and unlike the A-current of other neurons, it inactivates rapidly with complex inactivation kinetics. A-like current is half-inactivated at -63.5 mV and half-activated at -35.6 mV. 6. Our findings demonstrate for the first time in DUM neuron cell bodies the existence of multiple potassium currents underlying the spontaneous electrical activity. Their identification and characterization represent a fundamental step in further understanding the pacemaker properties of these insect neurosecretory cells.
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Wang, D. D., D. D. Krueger, and A. Bordey. "Biophysical Properties and Ionic Signature of Neuronal Progenitors of the Postnatal Subventricular Zone In Situ." Journal of Neurophysiology 90, no. 4 (October 2003): 2291–302. http://dx.doi.org/10.1152/jn.01116.2002.
Full textAbstract:
Previous studies have reported the presence of neuronal progenitors in the subventricular zone (SVZ) and rostral migratory stream (RMS) of the postnatal mammalian brain. Although many studies have examined the survival and migration of progenitors after transplantation and the factors influencing their proliferation or differentiation, no information is available on the electrophysiological properties of these progenitors in a near-intact environment. Thus we performed whole cell and cell-attached patch-clamp recordings of progenitors in brain slices containing either the SVZ or the RMS from postnatal day 15 to day 25 mice. Both regions displayed strong immunoreactivity for nestin and neuron-specific class III β-tubulin, and recorded cells displayed a morphology typical of the neuronal progenitors known to migrate throughout the SVZ and RMS to the olfactory bulb. Recorded progenitors had depolarized zero-current resting potentials (mean more depolarized than –28 mV), very high input resistances (about 4 GΩ), and lacked action potentials. Using the reversal potential of K+ currents through a cell-attached patch a mean resting potential of –59 mV was estimated. Recorded progenitors displayed Ca2+-dependent K+ currents and TEA-sensitive-delayed rectifying K+ (KDR) currents, but lacked inward K+ currents and transient outward K+ currents. KDR currents displayed classical kinetics and were also sensitive to 4-aminopyridine and α-dendrotoxin, a blocker of Kv1 channels. Na+ currents were found in about 60% of the SVZ neuronal progenitors. No developmental changes were observed in the passive membrane properties and current profile of neuronal progenitors. Together these data suggest that SVZ neuronal progenitors display passive membrane properties and an ionic signature distinct from that of cultured SVZ neuronal progenitors and mature neurons.
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Landeen, Lee K., Dorothy A. Dederko, Colleen S. Kondo, Betty S. Hu, Nakon Aroonsakool, Jason H. Haga, and Wayne R. Giles. "Mechanisms of the negative inotropic effects of sphingosine-1-phosphate on adult mouse ventricular myocytes." American Journal of Physiology-Heart and Circulatory Physiology 294, no. 2 (February 2008): H736—H749. http://dx.doi.org/10.1152/ajpheart.00316.2007.
Full textAbstract:
Sphingosine-1-phosphate (S1P) induces a transient bradycardia in mammalian hearts through activation of an inwardly rectifying K+ current ( IKACh) in the atrium that shortens action potential duration (APD) in the atrium. We have investigated probable mechanisms and receptor-subtype specificity for S1P-induced negative inotropy in isolated adult mouse ventricular myocytes. Activation of S1P receptors by S1P (100 nM) reduced cell shortening by ∼25% (vs. untreated controls) in field-stimulated myocytes. S1P1 was shown to be involved by using the S1P1-selective agonist SEW2871 on myocytes isolated from S1P3-null mice. However, in these myocytes, S1P3 can modulate a somewhat similar negative inotropy, as judged by the effects of the S1P1 antagonist VPC23019 . Since S1P1 activates Gi exclusively, whereas S1P3 activates both Gi and Gq, these results strongly implicate the involvement of mainly Gi. Additional experiments using the IKACh blocker tertiapin demonstrated that IKACh can contribute to the negative inotropy following S1P activation of S1P1 (perhaps through Giβγ subunits). Mathematical modeling of the effects of S1P on APD in the mouse ventricle suggests that shortening of APD (e.g., as induced by IKACh) can reduce L-type calcium current and thus can decrease the intracellular Ca2+ concentration ([Ca2+]i) transient. Both effects can contribute to the observed negative inotropic effects of S1P. In summary, these findings suggest that the negative inotropy observed in S1P-treated adult mouse ventricular myocytes may consist of two distinctive components: 1) one pathway that acts via Gi to reduce L-type calcium channel current, blunt calcium-induced calcium release, and decrease [Ca2+]i; and 2) a second pathway that acts via Gi to activate IKACh and reduce APD. This decrease in APD is expected to decrease Ca2+ influx and reduce [Ca2+]i and myocyte contractility.