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1
Triggle, David J. "Calcium, calcium channels, and calcium channel antagonists". Canadian Journal of Physiology and Pharmacology 68, n. 11 (1 novembre 1990): 1474–81. http://dx.doi.org/10.1139/y90-224.
Testo completoAbstract (sommario):
Voltage-dependent Ca2+ channels are an important pathway for Ca2+ influx in excitable cells. They also represent an important site of action for a therapeutic group of agents, the Ca2+ channel antagonists. These drugs enjoy considerable use in the cardiovascular area including angina, some arrhythmias, hypertension, and peripheral vascular disorders. The voltage-dependent Ca2+ channels exist in a number of subclasses characterized by electrophysiologic, permeation, and pharmacologic criteria. The Ca2+ channel antagonists, including verapamil, nifedipine, and diltiazem, serve to characterize the L channel class. This channel class has been characterized as a pharmacologic receptor, since it possesses specific drug-binding sites for both antagonists and activators and it is regulated by homologous and heterologous influences. The Ca2+ channels of both voltage- and ligand-regulated classes are likely to continue to be major research targets for new drug design and action.Key words: calcium, calcium channels, calcium antagonists, 1,4-dihydropyridines, channel regulation, receptor regulation.
2
Greenberg, David A. "Calcium channels and calcium channel antagonists". Annals of Neurology 21, n. 4 (aprile 1987): 317–30. http://dx.doi.org/10.1002/ana.410210402.
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3
Collier, M. L., G. Ji, Y. X. Wang e M. I. Kotlikoff. "Calcium-Induced Calcium Release in Smooth Muscle". Journal of General Physiology 115, n. 5 (1 maggio 2000): 653–62. http://dx.doi.org/10.1085/jgp.115.5.653.
Testo completoAbstract (sommario):
Calcium-induced calcium release (CICR) has been observed in cardiac myocytes as elementary calcium release events (calcium sparks) associated with the opening of L-type Ca2+ channels. In heart cells, a tight coupling between the gating of single L-type Ca2+ channels and ryanodine receptors (RYRs) underlies calcium release. Here we demonstrate that L-type Ca2+ channels activate RYRs to produce CICR in smooth muscle cells in the form of Ca2+ sparks and propagated Ca2+ waves. However, unlike CICR in cardiac muscle, RYR channel opening is not tightly linked to the gating of L-type Ca2+ channels. L-type Ca2+ channels can open without triggering Ca2+ sparks and triggered Ca2+ sparks are often observed after channel closure. CICR is a function of the net flux of Ca2+ ions into the cytosol, rather than the single channel amplitude of L-type Ca2+ channels. Moreover, unlike CICR in striated muscle, calcium release is completely eliminated by cytosolic calcium buffering. Thus, L-type Ca2+ channels are loosely coupled to RYR through an increase in global [Ca2+] due to an increase in the effective distance between L-type Ca2+ channels and RYR, resulting in an uncoupling of the obligate relationship that exists in striated muscle between the action potential and calcium release.
4
Mochida, Sumiko. "Presynaptic Calcium Channels". International Journal of Molecular Sciences 20, n. 9 (6 maggio 2019): 2217. http://dx.doi.org/10.3390/ijms20092217.
Testo completoAbstract (sommario):
Presynaptic Ca2+ entry occurs through voltage-gated Ca2+ (CaV) channels which are activated by membrane depolarization. Depolarization accompanies neuronal firing and elevation of Ca2+ triggers neurotransmitter release from synaptic vesicles. For synchronization of efficient neurotransmitter release, synaptic vesicles are targeted by presynaptic Ca2+ channels forming a large signaling complex in the active zone. The presynaptic CaV2 channel gene family (comprising CaV2.1, CaV2.2, and CaV2.3 isoforms) encode the pore-forming α1 subunit. The cytoplasmic regions are responsible for channel modulation by interacting with regulatory proteins. This article overviews modulation of the activity of CaV2.1 and CaV2.2 channels in the control of synaptic strength and presynaptic plasticity.
5
Gollasch, M., J. Hescheler, J. M. Quayle, J. B. Patlak e M. T. Nelson. "Single calcium channel currents of arterial smooth muscle at physiological calcium concentrations". American Journal of Physiology-Cell Physiology 263, n. 5 (1 novembre 1992): C948—C952. http://dx.doi.org/10.1152/ajpcell.1992.263.5.c948.
Testo completoAbstract (sommario):
Entry of Ca through voltage-dependent Ca channels is an important regulator of the function of smooth muscle, cardiac muscle, and neurons. Although Ca channels have been extensively studied since the first descriptions of Ca action potentials (P. Fatt and B. Katz. J. Physiol. Lond. 120: 171-204, 1953), the permeation rate of Ca through single Ca channels has not been measured directly under physiological conditions. Instead, single Ca channels have typically been examined using high concentrations (80-110 mM) of another divalent charge carrier, Ba, so as to maximize the amplitude of the single-channel currents. Calculations of unitary currents at 2 mM Ca indicated that the single-channel currents would be immeasurably small (i.e., < 0.1 pA). We provide here the first direct measurements of single Ca channel currents at a physiological Ca concentration. Contrary to earlier estimates, we have found that currents through single Ca channels in arterial smooth muscle are 0.1-0.3 pA at 2 mM Ca and physiological membrane potentials. These relatively large unitary currents permit direct measurement of Ca channel properties under conditions that do not distort their function. Our data also indicate that Ca permeates these channels at relatively high rates in physiological Ca concentrations and membrane potentials.
6
Shuttleworth, T. J., e O. Mignen. "Calcium entry and the control of calcium oscillations". Biochemical Society Transactions 31, n. 5 (1 ottobre 2003): 916–19. http://dx.doi.org/10.1042/bst0310916.
Testo completoAbstract (sommario):
During oscillatory Ca2+ signals, the agonist-induced enhanced entry of extracellular Ca2+ plays a critical role in modulating the frequency of the oscillations. Although it was originally assumed that the entry of Ca2+ under these conditions occurred via the well-known, and apparently ubiquitous, store-operated mechanism, subsequent studies suggested that this was unlikely. It is now known that, in many cell types, a novel non-capacitative Ca2+-selective pathway whose activation is dependent on arachidonic acid is responsible, and the channels involved [ARC channels (arachidonate-regulated Ca2+ channels)] have been characterized. These ARC channels co-exist with the store-operated CRAC channels (Ca2+-release-activated Ca2+ channel) in cells, but each plays a unique and non-overlapping role in Ca2+ signalling. In particular, it is the ARC channels that are specifically activated at the low agonist concentrations that give rise to oscillatory Ca2+ signals and provide the predominant mode of Ca2+ entry under these conditions. The indications are that Ca2+ entry through the ARC channels increases the likelihood that low concentrations of Ins(1,4,5)P3 will trigger repetitive Ca2+ release. At higher agonist concentrations, store-depletion is more complete and sustained resulting in the activation of CRAC channels. At the same time the ARC channels are turned off, resulting in what we have described as a reciprocal regulation of these two distinct Ca2+ entry pathways.
7
Triggle, C. R., e M. Wolowyk. "Calcium Channels Symposium". Canadian Journal of Physiology and Pharmacology 68, n. 11 (1 novembre 1990): 1472–73. http://dx.doi.org/10.1139/y90-223.
Testo completoAbstract (sommario):
Calcium is an essential element for just about all cellular processes, and yet abnormally high levels of cellular calcium can cause cell death. The processes that control cellular levels of this metal ion are thus of critical importance to both normal and pathophysiological conditions. Essential in the regulation of intracellular calcium levels are the calcium channels associated with cell membranes, for instance, with the plasma and sarcoplasmic reticulum membranes of muscle cells. In recent years, there has been a tremendous increase in our knowledge of the structure and function of these channels. However, we also now realize that the term "calcium channels" is used to refer to a rather heterogeneous population of entities. In some instances, notably receptor-operated calcium channels, we have only indirect evidence for their existence, whereas with the voltage-dependent channels, considerable information is now available on their comparative physiology, pharmacology, and biochemistry. The main objective of the Symposium presented in Calgary during the 1989 CFBS meeting was to bring together experts in the area of the calcium channels associated with both smooth and striated muscle function so that they could present the current state of knowledge in this area.Dr. David Triggle, from the State University of New York in Buffalo, reviewed the importance of calcium and calcium channels in cellular function and highlighted the pharmacology of calcium channel antagonists particularly with respect to their effects on the L-type calcium channels associated with smooth muscle. Dr. Sidney Fleischer from Vanderbilt University, Nashville, Tennessee, focused on his work associated with the isolation and characterization of the calcium release channel – ryanodine receptor of the sarcoplasmic reticulum from striated muscle. Dr. Fleischer has referred interested readers to his recent review in the 1989 issue of the Annual Reviews of Biophysics and Biophysical Chemistry (18: 333–364). Dr. Balwant Tuana from the University of Ottawa presented an update complemented by original data from his laboratory in the Department of Pharmacology on the current state of knowledge of the structure of the L-type calcium channel associated with both skeletal and cardiac muscle. The last two speakers, Dr. Wayne Giles and Dr. Hamid Akbarali, both from the Department of Medical Physiology at the University of Calgary, completed the program by presenting a review of data concerning the electrical physiological properties of calcium-activated channels in cardiac and smooth muscle. Their manuscript highlights their recent studies, with co-workers in Calgary, of the properties of calcium-activated potassium currents from the human cystic artery.The organizers of this symposium, hosted by the Pharmacological Society of Canada, gratefully acknowledge the financial support of the Alberta Heart and Stroke Foundation, Alberta Heritage Foundation for Medical Research, Canadian Heart and Stroke Foundation, Canadian Federation of Biological Societies, Charles River Laboratories (Canada Ltd.), SynPhar Laboratories Inc., Fisher Scientific Ltd., Novopharm Ltd., and Mandel Scientific Co. Ltd. The artistic contribution from Sylvia Ficken of Medical Audiovisual Services in the Faculty of Medicine at Memorial University of Newfoundland, who drew the symposium logo reproduced on the title page, is also gratefully acknowledged.
8
Friedman, P. A., e F. A. Gesek. "Hormone-responsive Ca2+ entry in distal convoluted tubules." Journal of the American Society of Nephrology 4, n. 7 (gennaio 1994): 1396–404. http://dx.doi.org/10.1681/asn.v471396.
Testo completoAbstract (sommario):
This editorial review focuses on recent observations regarding the mechanism and regulation of calcium transport in hormone-sensitive distal convoluted tubules. Parathyroid hormone (PTH) and calcitonin increase active calcium absorption by distal convoluted tubules. Occupancy of these peptide hormone receptors results in the activation of both protein kinase A and protein kinase C. The inhibition of either kinase blocks calcium transport. The time course of stimulation of calcium entry in distal convoluted tubules by PTH is slow compared with that by calcitonin. The latency associated with PTH action may be due to the induction of protein synthesis. PTH and calcitonin hyperpolarize membrane voltage, which in turn increases calcium entry. Calcium entry is mediated by calcium channels. These channels exhibit a low, single-channel conductance and are sensitive to dihydropyridine-type calcium channel blockers. Unlike L-type calcium channels, the channel open probability of distal convoluted tubule calcium entry channels is increased upon hyperpolarization. This novel combination of properties suggests that the underlying structure of these calcium entry channels may be unique.
9
Reuter, H., S. Kokubun e B. Prod'hom. "Properties and modulation of cardiac calcium channels". Journal of Experimental Biology 124, n. 1 (1 settembre 1986): 191–201. http://dx.doi.org/10.1242/jeb.124.1.191.
Testo completoAbstract (sommario):
Voltage-dependent calcium channels are widely distributed in excitable membranes and are involved in the regulation of many cellular functions. These channels can be modulated by neurotransmitters and drugs. There is one particular type of calcium channel in cardiac cells (L-type) whose gating is affected in different ways by beta-adrenoceptor and 1,4-dihydropyridine agonists. We have analysed single calcium channel currents (i) in myocytes from rat hearts in the absence and presence of isoproterenol or 8-bromo-cAMP. We have found that both compounds have similar effects on calcium channel properties. They increase the overall open state probability (po) of individual calcium channels while i remains unaffected. Analysis of the gating kinetics of calcium channels showed: a slight increase in the mean open times of calcium channels, a reduction in time intervals between bursts of channel openings, an increase in burst length and a prominent reduction in failures of calcium channels to open upon depolarization. These kinetic changes caused by isoproterenol and 8-bromo-cAMP can account for the increase in po. Since the macroscopic calcium current, ICa, can be described by ICa = N X po X i, the increase in po accounts for the well-known increase in ICa by beta-adrenergic catecholamines. Cyclic AMP-dependent phosphorylation of calcium channels is a likely metabolic step involved in this modulation. Another class of drug that modulates calcium channel gating is the 1,4-dihydropyridines which can either enhance or reduce ICa, either by prolonging the open state of the channels or by facilitating the inactivated state. Both effects depend strongly on membrane potential and are independent of cyclic AMP-dependent phosphorylation reactions.
10
Kolesnikov, D. O., E. R. Grigorieva, M. A. Nomerovskaya, D. S. Reshetin, A. V. Shalygin e E. V. Kaznacheyeva. "The Effect of Calcium Ions on the Electrophysiological Properties of Single ANO6 Channels". Acta Naturae 16, n. 1 (10 maggio 2024): 40–47. http://dx.doi.org/10.32607/actanaturae.27338.
Testo completoAbstract (sommario):
Proteins belonging to the anoctamin (ANO) family form calcium-activated chloride channels (CaCCs). The most unusual member of this family, ANO6 (TMEM16F), simultaneously exhibits the functions of calcium-dependent scramblase and the ion channel. ANO6 affects the plasma membrane dynamics and phosphatidylserine transport; it is also involved in programmed cell death. The properties of ANO6 channels remain the subject of debate. In this study, we investigated the effect of variations in the intracellular and extracellular concentrations of calcium ions on the electrophysiological properties of endogenous ANO6 channels by recording single ANO6 channels. It has been demonstrated that (1) a high calcium concentration in an extracellular solution increases the activity of endogenous ANO6 channels, (2) the permeability of endogenous ANO6 channels for chloride ions is independent of the extracellular concentration of calcium ions, (3) that an increase in the intracellular calcium concentration leads to the activation of endogenous ANO6 channels with double amplitude, and (4) that the kinetics of the channel depend on the plasma membrane potential rather than the intracellular concentration of calcium ions. Our findings give grounds for proposing new mechanisms for the regulation of the ANO6 channel activity by calcium ions both at the inner and outer sides of the membrane.
11
Rosenberg, R. L., P. Hess e R. W. Tsien. "Cardiac calcium channels in planar lipid bilayers. L-type channels and calcium-permeable channels open at negative membrane potentials." Journal of General Physiology 92, n. 1 (1 luglio 1988): 27–54. http://dx.doi.org/10.1085/jgp.92.1.27.
Testo completoAbstract (sommario):
Planar lipid bilayer recordings were used to study Ca channels from bovine cardiac sarcolemmal membranes. Ca channel activity was recorded in the absence of nucleotides or soluble enzymes, over a range of membrane potentials and ionic conditions that cannot be achieved in intact cells. The dihydropyridine-sensitive L-type Ca channel, studied in the presence of Bay K 8644, was identified by a detailed comparison of its properties in artificial membranes and in intact cells. L-type Ca channels in bilayers showed voltage dependence of channel activation and inactivation, open and closed times, and single-channel conductances in Ba2+ and Ca2+ very similar to those found in cell-attached patch recordings. Open channels were blocked by micromolar concentrations of external Cd2+. In this cell-free system, channel activity tended to decrease during the course of an experiment, reminiscent of Ca2+ channel "rundown" in whole-cell and excised-patch recordings. A purely voltage-dependent component of inactivation was observed in the absence of Ca2+ stores or changes in intracellular Ca2+. Millimolar internal Ca2+ reduced unitary Ba2+ influx but did not greatly increase the rate or extent of inactivation or the rate of channel rundown. In symmetrical Ba2+ solutions, unitary conductance saturated as the Ba2+ concentration was increased up to 500 mM. The bilayer recordings also revealed activity of a novel Ca2+-permeable channel, termed "B-type" because it may contribute a steady background current at negative membrane potentials, which is distinct from L-type or T-type Ca channels previously reported. Unlike L-type channels, B-type channels have a small unitary Ba2+ conductance (7 pS), but do not discriminate between Ba2+ and Ca2+, show no obvious sensitivity to Bay K 8644, and do not run down. Unlike either L- or T-type channels, B-type channels did not require a depolarization for activation and displayed mean open times of greater than 100 ms.
12
BIEDA, MARK C., e DAVID R. COPENHAGEN. "N-type and L-type calcium channels mediate glycinergic synaptic inputs to retinal ganglion cells of tiger salamanders". Visual Neuroscience 21, n. 4 (luglio 2004): 545–50. http://dx.doi.org/10.1017/s0952523804214055.
Testo completoAbstract (sommario):
Synaptically localized calcium channels shape the timecourse of synaptic release, are a prominent site for neuromodulation, and have been implicated in genetic disease. In retina, it is well established that L-type calcium channels play a major role in mediating release of glutamate from the photoreceptors and bipolar cells. However, little is known about which calcium channels are coupled to synaptic exocytosis of glycine, which is primarily released by amacrine cells. A recent report indicates that glycine release from spiking AII amacrine cells relies exclusively upon L-type calcium channels. To identify calcium channel types controlling neurotransmitter release from the population of glycinergic neurons that drive retinal ganglion cells, we recorded electrical and potassium evoked inhibitory synaptic currents (IPSCs) from these postsynaptic neurons in retinal slices from tiger salamanders. The L-channel antagonist nifedipine strongly inhibited release and FPL64176, an L-channel agonist, greatly enhanced it, indicating a significant role for L-channels. ω-Conotoxin MVIIC, an N/P/Q-channel antagonist, strongly inhibited release, indicating an important role for non-L channels. While the P/Q-channel blocker ω-Aga IVA produced only small effects, the N-channel blocker ω-conotoxin GVIA strongly inhibited release. Hence, N-type and L-type calcium channels appear to play major roles, overall, in mediating synaptic release of glycine onto retinal ganglion cells.
13
Glossmann, H., D. R. Ferry, A. Goll, J. Striessnig e M. Schober. "Calcium Channels". Journal of Cardiovascular Pharmacology 7 (1985): S20—S30. http://dx.doi.org/10.1097/00005344-198500076-00005.
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Rodger, Ian W. "Calcium Channels". American Review of Respiratory Disease 136, n. 4_pt_2 (ottobre 1987): S15—S17. http://dx.doi.org/10.1164/ajrccm/136.4_pt_2.s15.
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PETERSEN, O. H. "Calcium channels". Nature 336, n. 6199 (dicembre 1988): 528. http://dx.doi.org/10.1038/336528a0.
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Yu, Alan S. L. "Calcium channels". Current Opinion in Nephrology and Hypertension 3, n. 5 (settembre 1994): 497–503. http://dx.doi.org/10.1097/00041552-199409000-00004.
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Schwartz, Arnold. "Calcium channels". Journal of Molecular and Cellular Cardiology 24 (maggio 1992): 33. http://dx.doi.org/10.1016/0022-2828(92)90130-r.
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Luo, Fujun, Markus Dittrich, Soyoun Cho, Joel R. Stiles e Stephen D. Meriney. "Transmitter release is evoked with low probability predominately by calcium flux through single channel openings at the frog neuromuscular junction". Journal of Neurophysiology 113, n. 7 (aprile 2015): 2480–89. http://dx.doi.org/10.1152/jn.00879.2014.
Testo completoAbstract (sommario):
The quantitative relationship between presynaptic calcium influx and transmitter release critically depends on the spatial coupling of presynaptic calcium channels to synaptic vesicles. When there is a close association between calcium channels and synaptic vesicles, the flux through a single open calcium channel may be sufficient to trigger transmitter release. With increasing spatial distance, however, a larger number of open calcium channels might be required to contribute sufficient calcium ions to trigger vesicle fusion. Here we used a combination of pharmacological calcium channel block, high-resolution calcium imaging, postsynaptic recording, and 3D Monte Carlo reaction-diffusion simulations in the adult frog neuromuscular junction, to show that release of individual synaptic vesicles is predominately triggered by calcium ions entering the nerve terminal through the nearest open calcium channel. Furthermore, calcium ion flux through this channel has a low probability of triggering synaptic vesicle fusion (∼6%), even when multiple channels open in a single active zone. These mechanisms work to control the rare triggering of vesicle fusion in the frog neuromuscular junction from each of the tens of thousands of individual release sites at this large model synapse.
19
McCleskey, E. W., A. P. Fox, D. Feldman e R. W. Tsien. "Different types of calcium channels". Journal of Experimental Biology 124, n. 1 (1 settembre 1986): 177–90. http://dx.doi.org/10.1242/jeb.124.1.177.
Testo completoAbstract (sommario):
Ca2+ channels allow passage of Ca2+ ions into the cytoplasm through a selective pore which is opened in response to depolarization of the cell membrane (for reviews see Hagiwara & Byerly, 1981, 1983; Tsien, 1983; Reuter, 1983). The Ca2+ flux creates a net inward, depolarizing current and the resulting accumulation of Ca2+ in the cytoplasm can act as a chemical trigger for secretion of hormones and neurotransmitters, contraction of muscle and a variety of other Ca2+-sensitive events. Thus, upon sensing membrane potential changes, Ca2+ channels simultaneously generate an electrical signal while directly creating an intracellular chemical messenger. This dual ability is unique among the family of ion channels and allows the Ca2+ channel to play a variety of roles in excitation-secretion and excitation-contraction coupling. It has now become clear that versatility of function is reflected by diversity of the types of Ca2+ channels on the membrane of individual cells. This article describes the nature of data which have demonstrated multiple channel types, reviews the literature suggesting that many cells have several kinds of Ca2+ channels, and discusses newer data regarding a neurotoxin that distinguishes among different Ca2+ channels.
20
Fill, Michael, e Julio A. Copello. "Ryanodine Receptor Calcium Release Channels". Physiological Reviews 82, n. 4 (10 gennaio 2002): 893–922. http://dx.doi.org/10.1152/physrev.00013.2002.
Testo completoAbstract (sommario):
The ryanodine receptors (RyRs) are a family of Ca2+ release channels found on intracellular Ca2+ storage/release organelles. The RyR channels are ubiquitously expressed in many types of cells and participate in a variety of important Ca2+ signaling phenomena (neurotransmission, secretion, etc.). In striated muscle, the RyR channels represent the primary pathway for Ca2+ release during the excitation-contraction coupling process. In general, the signals that activate the RyR channels are known (e.g., sarcolemmal Ca2+ influx or depolarization), but the specific mechanisms involved are still being debated. The signals that modulate and/or turn off the RyR channels remain ambiguous and the mechanisms involved unclear. Over the last decade, studies of RyR-mediated Ca2+ release have taken many forms and have steadily advanced our knowledge. This robust field, however, is not without controversial ideas and contradictory results. Controversies surrounding the complex Ca2+ regulation of single RyR channels receive particular attention here. In addition, a large body of information is synthesized into a focused perspective of single RyR channel function. The present status of the single RyR channel field and its likely future directions are also discussed.
21
Braun, Andrew P. "Ammonium ion enhances the calcium-dependent gating of a mammalian large conductance, calcium-sensitive K+ channel". Canadian Journal of Physiology and Pharmacology 79, n. 11 (1 novembre 2001): 919–23. http://dx.doi.org/10.1139/y01-076.
Testo completoAbstract (sommario):
We observed that the current amplitude and activation of expressed, mouse brain large conductance, calcium-sensitive K+ channels (BKCa channels) may be reversibly enhanced following addition of low concentrations of the weakly permeant cation NH4+ to the cytoplasmic face of the channel in excised, inside-out membrane patches from HEK 293 cells. Conductance-voltage relations were left-shifted along the voltage axis by addition of NH4Cl in a concentration-dependent manner, with an EC50 of 18.5 mM. Furthermore, this effect was observed in the presence of cytosolic free calcium (~1 µM), but was absent in a cytosolic bath solution containing nominally zero free calcium (e.g., 5 mM EGTA only), a condition under which these channels undergo largely voltage-dependent gating. Recordings of single BKCa channel events indicated that NH4+ increased the channel open probability of single channel activity ~3-fold, but did not alter the amplitude of single channel currents. These findings suggest that the calcium-sensitive gating of mammalian BKCa channels may be modified by other ions present in cytosolic solution.Key words: potassium channel, calcium, modulation, electrophysiology.
22
Vasu, Sreerag Othayoth, e Hanoch Kaphzan. "Direct Current Stimulation Modulates Synaptic Facilitation via Distinct Presynaptic Calcium Channels". International Journal of Molecular Sciences 24, n. 23 (28 novembre 2023): 16866. http://dx.doi.org/10.3390/ijms242316866.
Testo completoAbstract (sommario):
Transcranial direct current stimulation (tDCS) is a subthreshold neurostimulation technique known for ameliorating neuropsychiatric conditions. The principal mechanism of tDCS is the differential polarization of subcellular neuronal compartments, particularly the axon terminals that are sensitive to external electrical fields. Yet, the underlying mechanism of tDCS is not fully clear. Here, we hypothesized that direct current stimulation (DCS)-induced modulation of presynaptic calcium channel conductance alters axon terminal dynamics with regard to synaptic vesicle release. To examine the involvement of calcium-channel subtypes in tDCS, we recorded spontaneous excitatory postsynaptic currents (sEPSCs) from cortical layer-V pyramidal neurons under DCS while selectively inhibiting distinct subtypes of voltage-dependent calcium channels. Blocking P/Q or N-type calcium channels occluded the effects of DCS on sEPSCs, demonstrating their critical role in the process of DCS-induced modulation of spontaneous vesicle release. However, inhibiting T-type calcium channels did not occlude DCS-induced modulation of sEPSCs, suggesting that despite being active in the subthreshold range, T-type calcium channels are not involved in the axonal effects of DCS. DCS modulates synaptic facilitation by regulating calcium channels in axon terminals, primarily via controlling P/Q and N-type calcium channels, while T-type calcium channels are not involved in this mechanism.
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Manira, A. El, e N. Bussières. "Calcium Channel Subtypes in Lamprey Sensory and Motor Neurons". Journal of Neurophysiology 78, n. 3 (1 settembre 1997): 1334–40. http://dx.doi.org/10.1152/jn.1997.78.3.1334.
Testo completoAbstract (sommario):
El Manira, A. and N. Bussières. Calcium channel subtypes in lamprey sensory and motor neurons. J. Neurophysiol. 78: 1334–1340, 1997. Pharmacologically distinct calcium channels have been characterized in dissociated cutaneous sensory neurons and motoneurons of the larval lamprey spinal cord. To enable cell identification, sensory dorsal cells and motoneurons were selectively labeled with fluorescein-coupled dextran amine in the intact spinal cord in vitro before dissociation. Calcium channels present in sensory dorsal cells, motoneurons, and other spinal cord neurons were characterized with the use of whole cell voltage-clamp recordings and specific calcium channel agonist and antagonists. The results show that a transient low-voltage-activated (LVA) calcium current was present in a proportion of sensory dorsal cells but not in motoneurons, whereas high-voltage-activated (HVA) calcium currents were seen in all neurons recorded. The different components of HVA current were dissected pharmacologically and similar results were obtained for both dorsal cells and motoneurons. The N-type calcium channel antagonist ω-conotoxin-GVIA(ω-CgTx) blocked >70% of the HVA current. A large part of the ω-CgTx block was reversed after washout of the toxin. The L-type calcium channel antagonist nimodipine blocked ∼15% of the total HVA current. The dihydropyridine agonist (±)-BayK 8644 markedly increased the amplitude of the calcium channel current. The BayK-potentiated current was not affected by ω-CgTx, indicating that the reversibility of the ω-CgTx effect is not due to a blockade of L-type channels. Simultaneous application of ω-CgTx and nimodipine left ∼15% of the HVA calcium channel current, a small part of which was blocked by the P/Q-type channel antagonist ω-agatoxin-IVA. In the presence of the three antagonists, the persistent residual current (∼10%) was completely blocked by cadmium. Our results provide evidence for the existence of HVA calcium channels of the N, L, and P/Q types and other HVA calcium channels in lamprey sensory neurons and motoneurons. In addition, certain types of neurons express LVA calcium channels.
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Bennett, Brian D., Ulises Alvarez e Keith A. Hruska. "Receptor-Operated Osteoclast Calcium Sensing*". Endocrinology 142, n. 5 (1 maggio 2001): 1968–74. http://dx.doi.org/10.1210/endo.142.5.8125.
Testo completoAbstract (sommario):
Abstract Osteoclasts “sense” elevated extracellular calcium, which leads to cytoskeletal changes that may be linked to phospholipase C (PLC) activation and the associated rise in intracellular calcium ([Ca2+]i). Since PLC is linked to transient receptor potential channels (trp), we hypothesized that receptor activated calcium influx due to this channel type would be activated by osteoclasts sensing [Ca2+]e. We found that high [Ca2+]e induced similar intracellular Ca2+ rises in chicken osteoclasts with or without intracellular Ca2+ store depletion by either TPEN or thapsigargin, thus defining store-insensitive Ca2+ influx. This store-insensitive calcium sensing component was blocked by the PLC antagonist U73122. Also, the calcium channel inhibitor SKF 96365, a blocker of store-independent trp-like channels, was effective in inhibiting calcium sensing in the presence of thapsigargin. Thus, a store-independent component of calcium sensing was associated with ion channels linked to PLC. Since receptor activated transient receptor potential (trp) family cation channels open in a PLC-dependent and store-independent manner, we suggest that receptor operated channels are activated in osteoclasts stimulated by high extracellular Ca2+.
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Seagar, Michael, Christian Lévêque, Nathalie Charvin, Beatrice Marquèze, Nicole Martin–Moutot, Jeanne Andrée Boudier, Jean–Louis Boudier, Yoko Shoji-Kasai, Kazuki Sato e Masami Takahashi. "Interactions between proteins implicated in exocytosis and voltage–gated calcium channels". Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 354, n. 1381 (28 febbraio 1999): 289–97. http://dx.doi.org/10.1098/rstb.1999.0380.
Testo completoAbstract (sommario):
Neurotransmitter release from synaptic vesicles is triggered by voltage–gated calcium influx through P/Q–type or N–type calcium channels. Purification of N–type channels from rat brain synaptosomes initially suggested molecular interactions between calcium channels and two key proteins implicated in exocytosis: synaptotagmin I and syntaxin 1. Co–immunoprecipitation experiments were consistent with the hypothesis that both N– and P/Q–type calcium channels, but not L–type channels, are associated with the 7S complex containing syntaxin 1, SNAP–25, VAMP and synaptotagmin I or II. Immunofluorescence confocal microscopy at the frog neuromuscular junction confirmed that calcium channels, syntaxin 1 and SNAP–25 are co–localized at active zones of the presynaptic plasma membrane where transmitter release occurs. Experiments with recombinant proteins were performed to map synaptic protein interaction sites on the α 1 A subunit, which forms the pore of the P/Q–type calcium channel. In vitro –translated 35 S–synaptotagmin I bound to a site located on the cytoplasmic loop linking homologous domains II and III of the α 1 A subunit. This direct link would target synaptotagmin, a putative calcium sensor for exocytosis, to a microdomain of calcium influx close to the channel mouth. Cysteine string proteins (CSPs) contain a J–domain characteristic of molecular chaperones that co–operate with Hsp70. They are located on synaptic vesicles and thought to be involved in modulating the acticity of presynaptic calcium channels. CSPs were found to bind to the same domain of the calcium channel as synaptotagmin, and also to associate with VAMP. CSPs may act as molecular chaperones in association with Hsp70 to direct assembly or dissociation of multi–protein complexes at the calcium channel.
26
Mangel, A. W., L. Scott e R. A. Liddle. "Depolarization-stimulated cholecystokinin secretion is mediated by L-type calcium channels in STC-1 cells". American Journal of Physiology-Gastrointestinal and Liver Physiology 270, n. 2 (1 febbraio 1996): G287—G290. http://dx.doi.org/10.1152/ajpgi.1996.270.2.g287.
Testo completoAbstract (sommario):
To examine the role of calcium channels in depolarization-activated cholecystokinin (CCK) release, studies were performed in an intestinal CCK-secreting cell line, STC-1. Blockade of potassium channels with barium chloride (5 mM) increased the release of CCK by 374.6 +/- 46.6% of control levels. Barium-induced secretion was inhibited by the L-type calcium-channel blocker, nicardipine. Nicardipine (10(-9)-10(-5) M) produced a dose-dependent inhibition in barium-stimulated secretion with a half-maximal inhibition (IC50) value of 0.1 microM. A second L-type calcium-channel blocker, diltiazem (10(-9)-10(-4) M), also inhibited barium-induced CCK secretion with an IC50 value of 5.1 microM. By contrast, the T-type calcium-channel blocker, nickel chloride (10(-7)-10(-8) M), failed to significantly inhibit barium-induced CCK secretion. To further evaluate a role for L-type calcium channels in the secretion of CCK, the effects of the L-type calcium channel opener, BAY K 8644, were examined. BAY K 8644 (10(-8)-10(-4) M) produced a dose-dependent stimulation in CCK release with a mean effective concentration value of 0.2 microM. Recordings of single-channel currents from inside-out membrane patches showed activation of calcium channels by BAY K 8644 (1 microM), with a primary channel conductance of 26.0 +/- 1.2 pS. It is concluded that inhibition of potassium channel activity depolarizes the plasma membrane, thereby activating L-type, but not T-type, calcium channels. The corresponding influx of calcium serves to trigger secretion of CCK.
27
Mayo, Sonia, Irene Gómez-Manjón, Ana Victoria Marco-Hernández, Francisco Javier Fernández-Martínez, Ana Camacho e Francisco Martínez. "N-Type Ca Channel in Epileptic Syndromes and Epilepsy: A Systematic Review of Its Genetic Variants". International Journal of Molecular Sciences 24, n. 7 (23 marzo 2023): 6100. http://dx.doi.org/10.3390/ijms24076100.
Testo completoAbstract (sommario):
N-type voltage-gated calcium channel controls the release of neurotransmitters from neurons. The association of other voltage-gated calcium channels with epilepsy is well-known. The association of N-type voltage-gated calcium channels and pain has also been established. However, the relationship between this type of calcium channel and epilepsy has not been specifically reviewed. Therefore, the present review systematically summarizes existing publications regarding the genetic associations between N-type voltage-dependent calcium channel and epilepsy.
28
Pallotta, B. S. "N-bromoacetamide removes a calcium-dependent component of channel opening from calcium-activated potassium channels in rat skeletal muscle." Journal of General Physiology 86, n. 5 (1 novembre 1985): 601–11. http://dx.doi.org/10.1085/jgp.86.5.601.
Testo completoAbstract (sommario):
Calcium-activated potassium channels from cultured rat skeletal muscle were treated with the protein-modifying reagent N-bromoacetamide (NBA) (0.3-1 mM) and studied in excised patches using patch-clamp techniques. After NBA treatment, channels opened only occasionally, and, in contrast to untreated channels, the open probability was no longer sensitive to intracellular surface calcium ions (1 nM to 100 microM). Channel activity did, however, exhibit a voltage dependence similar in direction and magnitude to that shown before NBA treatment (increasing e-fold with 19 mV depolarization). Distributions of open channel lifetimes revealed that NBA treatment virtually abolished openings of long duration, which suggests that this class of openings requires calcium sensitivity. These effects were not reversed by subsequent washing. Quantitatively similar open probability, voltage dependence, and open-interval distributions were observed in untreated channels in calcium-free medium. These results suggest that NBA removed a calcium-dependent component of channel opening, and that normal channels are able to open in the absence of significant intracellular calcium concentrations.
29
Noyer, Lucile, Loic Lemonnier, Pascal Mariot e Dimitra Gkika. "Partners in Crime: Towards New Ways of Targeting Calcium Channels". International Journal of Molecular Sciences 20, n. 24 (16 dicembre 2019): 6344. http://dx.doi.org/10.3390/ijms20246344.
Testo completoAbstract (sommario):
The characterization of calcium channel interactome in the last decades opened a new way of perceiving ion channel function and regulation. Partner proteins of ion channels can now be considered as major components of the calcium homeostatic mechanisms, while the reinforcement or disruption of their interaction with the channel units now represents an attractive target in research and therapeutics. In this review we will focus on the targeting of calcium channel partner proteins in order to act on the channel activity, and on its consequences for cell and organism physiology. Given the recent advances in the partner proteins’ identification, characterization, as well as in the resolution of their interaction domain structures, we will develop the latest findings on the interacting proteins of the following channels: voltage-dependent calcium channels, transient receptor potential and ORAI channels, and inositol 1,4,5-trisphosphate receptor.
30
Davis, Scott F., e Cindy L. Linn. "Mechanism linking NMDA receptor activation to modulation of voltage-gated sodium current in distal retina". American Journal of Physiology-Cell Physiology 284, n. 5 (1 maggio 2003): C1193—C1204. http://dx.doi.org/10.1152/ajpcell.00256.2002.
Testo completoAbstract (sommario):
In this study, we investigated the mechanism that links activation of N-methyl-D-aspartate (NMDA) receptors to inhibition of voltage-gated sodium channels in isolated catfish cone horizontal cells. NMDA channels were activated in voltage-clamped cells incubated in low-calcium saline or dialyzed with the calcium chelator BAPTA to determine that calcium influx through NMDA channels is required for sodium channel modulation. To determine whether calcium influx through NMDA channels triggers calcium-induced calcium release (CICR), cells were loaded with the calcium-sensitive dye calcium green 2 and changes in relative fluorescence were measured in response to NMDA. Responses were compared with measurements obtained when caffeine depleted stores. Voltage-clamp studies demonstrated that CICR modulated sodium channels in a manner similar to that of NMDA. Blocking NMDA receptors with AP-7, blocking CICR with ruthenium red, depleting stores with caffeine, or dialyzing cells with calmodulin antagonists W-5 or peptide 290–309 all prevented sodium channel modulation. These results support the hypothesis that NMDA modulation of voltage-gated sodium channels in horizontal cells requires CICR and activation of a calmodulin-dependent signaling pathway.
31
Pozdnyakov, Ilya, Olga Matantseva e Sergei Skarlato. "Consensus channelome of dinoflagellates revealed by transcriptomic analysis sheds light on their physiology". Algae 36, n. 4 (15 dicembre 2021): 315–26. http://dx.doi.org/10.4490/algae.2021.36.12.2.
Testo completoAbstract (sommario):
Ion channels are membrane protein complexes mediating passive ion flux across the cell membranes. Every organism has a certain set of ion channels that define its physiology. Dinoflagellates are ecologically important microorganisms characterized by effective physiological adaptability, which backs up their massive proliferations that often result in harmful blooms (red tides). In this study, we used a bioinformatics approach to identify homologs of known ion channels that belong to 36 ion channel families. We demonstrated that the versatility of the dinoflagellate physiology is underpinned by a high diversity of ion channels including homologs of animal and plant proteins, as well as channels unique to protists. The analysis of 27 transcriptomes allowed reconstructing a consensus ion channel repertoire (channelome) of dinoflagellates including the members of 31 ion channel families: inwardly-rectifying potassium channels, two-pore domain potassium channels, voltage-gated potassium channels (Kv), tandem Kv, cyclic nucleotide-binding domain-containing channels (CNBD), tandem CNBD, eukaryotic ionotropic glutamate receptors, large-conductance calcium-activated potassium channels, intermediate/small-conductance calcium-activated potassium channels, eukaryotic single-domain voltage-gated cation channels, transient receptor potential channels, two-pore domain calcium channels, four-domain voltage-gated cation channels, cation and anion Cys-loop receptors, small-conductivity mechanosensitive channels, large-conductivity mechanosensitive channels, voltage-gated proton channels, inositole-1,4,5- trisphosphate receptors, slow anion channels, aluminum-activated malate transporters and quick anion channels, mitochondrial calcium uniporters, voltage-dependent anion channels, vesicular chloride channels, ionotropic purinergic receptors, animal volage-insensitive cation channels, channelrhodopsins, bestrophins, voltage-gated chloride channels H+/Cl- exchangers, plant calcium-permeable mechanosensitive channels, and trimeric intracellular cation channels. Overall, dinoflagellates represent cells able to respond to physical and chemical stimuli utilizing a wide range of Gprotein coupled receptors- and Ca2+-dependent signaling pathways. The applied approach not only shed light on the ion channel set in dinoflagellates, but also provided the information on possible molecular mechanisms underlying vital cellular processes dependent on the ion transport.
32
Taylor, James T., Luping Huang, Brian M. Keyser, Hean Zhuang, Craig W. Clarkson e Ming Li. "Role of high-voltage-activated calcium channels in glucose-regulated β-cell calcium homeostasis and insulin release". American Journal of Physiology-Endocrinology and Metabolism 289, n. 5 (novembre 2005): E900—E908. http://dx.doi.org/10.1152/ajpendo.00101.2005.
Testo completoAbstract (sommario):
High-voltage-activated (HVA) calcium channels are known to be the primary source of calcium for glucose-stimulated insulin secretion. However, few studies have investigated how these channels can be regulated by chronically elevated levels of glucose. In the present study, we determined the level of expression of the four major HVA calcium channels (N-type, P/Q-type, LC-type, and LD-type) in rat pancreatic β-cells. Using quantitative real-time PCR (QRT-PCR), we found the expression of all four HVA genes in rat insulinoma cells (INS-1) and in primary isolated rat islet cells. We then determined the role of each channel in insulin secretion by using channel-selective antagonists. Insulin secretion analysis revealed that N- and L-type channels are both involved in immediate glucose-induced insulin secretion. However, L-type was preferentially coupled to secretion at later time points. P/Q-type channels were not found to play a role in insulin secretion at any stage. It was also found that long-term exposure to elevated glucose increases basal calcium in these cells. Interestingly, chronically elevated glucose decreased the mRNA expression of the channels involved with insulin secretion and diminished the level of stimulated calcium influx in these cells. Using whole cell patch clamp, we found that N- and L-type channel currents increase gradually subsequent to lower intracellular calcium perfusion, suggesting that these channels may be regulated by glucose-induced changes in calcium.
33
Putney, James W. "Capacitative calcium entry". Journal of Cell Biology 169, n. 3 (2 maggio 2005): 381–82. http://dx.doi.org/10.1083/jcb.200503161.
Testo completoAbstract (sommario):
A long-standing mystery in the cell biology of calcium channel regulation is the nature of the signal linking intracellular calcium stores to plasma membrane capacitative calcium entry channels. An RNAi-based screen of selected Drosophila genes has revealed that a calcium-binding protein, stromal interaction molecule (STIM), plays an essential role in the activation of these channels and may be the long sought sensor of calcium store content.
34
Estacion, M., H. B. Nguyen e J. J. Gargus. "Calcium is permeable through a maitotoxin-activated nonselective cation channel in mouse L cells". American Journal of Physiology-Cell Physiology 270, n. 4 (1 aprile 1996): C1145—C1152. http://dx.doi.org/10.1152/ajpcell.1996.270.4.c1145.
Testo completoAbstract (sommario):
The shellfish poison maitotoxin causes the irreversible opening of nonselective cation channels in mouse L cell fibroblasts, consistent with the action of this toxin in other cell types and the previously demonstrated existence of 28-pS voltage-insensitive nonselected cation channels that are activated by platelet-derived growth factor in these cells. Toxin-induced opening of these nonselective cation channels led to increases of intracellular calcium and secondary activation of calcium-activated potassium channel. These effects were completely dependent on influx of extracellular calcium, supporting the conclusion that the maitotoxin-activated nonselective cation channels are permeable to calcium as well as to sodium and potassium. The implication of this finding is that calcium signaling through this channel underlies its links into the growth factor response.
35
Mendelowitz, D., P. J. Reynolds e M. C. Andresen. "Heterogeneous functional expression of calcium channels at sensory and synaptic regions in nodose neurons". Journal of Neurophysiology 73, n. 2 (1 febbraio 1995): 872–75. http://dx.doi.org/10.1152/jn.1995.73.2.872.
Testo completoAbstract (sommario):
1. In the present study we have taken advantage of the unique anatomy of visceral sensory neurons that enabled us to isolate and examine the role of calcium channel subtypes at the soma, central synaptic terminals, and peripheral sensory endings. 2. N-type calcium channels dominated somatic currents (60%), with lesser (16% and 12%) contributions from P- and L-type channels, respectively, in patch-clamped dispersed nodose neurons using toxins selective for each calcium channel subtype. 3. These toxins also blocked the release of neurotransmitters from these visceral synaptic terminals in a brain stem slice. Similar to the profile at the soma, N-type calcium channels were most responsible for neurotransmission at this central glutamatergic synapse (57%), with P- and L-type channels making small contributions (12% and 11%, respectively). 4. In contrast to the soma and central synapses, these calcium channel toxins failed to affect the sensory transduction at aortic baroreceptor endings. 5. Therefore calcium channel subtypes have dramatically heterogenous distributions in sensory neurons that presumably subserve the specialized functions that occur at different cellular regions.
36
Hyde, James, Nebojsa Kezunovic, Francisco J. Urbano e Edgar Garcia-Rill. "Spatiotemporal properties of high-speed calcium oscillations in the pedunculopontine nucleus". Journal of Applied Physiology 115, n. 9 (1 novembre 2013): 1402–14. http://dx.doi.org/10.1152/japplphysiol.00762.2013.
Testo completoAbstract (sommario):
The pedunculopontine nucleus (PPN) is a component of the reticular activating system (RAS), and is involved in the activated states of waking and rapid eye movement (REM) sleep. Gamma oscillations (approximately 30–80 Hz) are evident in all PPN neurons and are mediated by high-threshold voltage-dependent N- and P/Q-type calcium channels. We tested the hypothesis that high-speed calcium imaging would reveal calcium-mediated oscillations in dendritic compartments in synchrony with patch-clamp recorded oscillations during depolarizing current ramps. Patch-clamped 8- to 16-day-old rat PPN neurons ( n = 67 out of 121) were filled with Fura 2, Bis Fura, or OGB1/CHR. This study also characterized a novel ratiometric technique using Oregon Green BAPTA-1 (OGB1) with coinjections of a new long-stokes-shift dye, Chromeo 494 (CHR). Fluorescent calcium transients were blocked with the nonspecific calcium channel blocker cadmium, or by the combination of ω-agatoxin-IVA, a specific P/Q-type calcium channel blocker, and ω-conotoxin-GVIA, a specific N-type calcium channel blocker. The calcium transients were evident in different dendrites (suggesting channels are present throughout the dendritic tree) along the sampled length without interruption (suggesting channels are evenly distributed), and appeared to represent a summation of oscillations present in the soma. We confirm that PPN calcium channel-mediated oscillations are due to P/Q- and N-type channels, and reveal that these channels are distributed along the dendrites of PPN cells.
37
Isaev, Dmytro, Karisa Solt, Oksana Gurtovaya, John P. Reeves e Roman Shirokov. "Modulation of the Voltage Sensor of L-type Ca2+ Channels by Intracellular Ca2+". Journal of General Physiology 123, n. 5 (26 aprile 2004): 555–71. http://dx.doi.org/10.1085/jgp.200308876.
Testo completoAbstract (sommario):
Both intracellular calcium and transmembrane voltage cause inactivation, or spontaneous closure, of L-type (CaV1.2) calcium channels. Here we show that long-lasting elevations of intracellular calcium to the concentrations that are expected to be near an open channel (≥100 μM) completely and reversibly blocked calcium current through L-type channels. Although charge movements associated with the opening (ON) motion of the channel's voltage sensor were not altered by high calcium, the closing (OFF) transition was impeded. In two-pulse experiments, the blockade of calcium current and the reduction of gating charge movements available for the second pulse developed in parallel during calcium load. The effect depended steeply on voltage and occurred only after a third of the total gating charge had moved. Based on that, we conclude that the calcium binding site is located either in the channel's central cavity behind the voltage-dependent gate, or it is formed de novo during depolarization through voltage-dependent rearrangements just preceding the opening of the gate. The reduction of the OFF charge was due to the negative shift in the voltage dependence of charge movement, as previously observed for voltage-dependent inactivation. Elevation of intracellular calcium concentration from ∼0.1 to 100–300 μM sped up the conversion of the gating charge into the negatively distributed mode 10–100-fold. Since the “IQ-AA” mutant with disabled calcium/calmodulin regulation of inactivation was affected by intracellular calcium similarly to the wild-type, calcium/calmodulin binding to the “IQ” motif apparently is not involved in the observed changes of voltage-dependent gating. Although calcium influx through the wild-type open channels does not cause a detectable negative shift in the voltage dependence of their charge movement, the shift was readily observable in the Δ1733 carboxyl terminus deletion mutant, which produces fewer nonconducting channels. We propose that the opening movement of the voltage sensor exposes a novel calcium binding site that mediates inactivation.
38
Yan, Jiusheng, Qin Li e Richard W. Aldrich. "Closed state-coupled C-type inactivation in BK channels". Proceedings of the National Academy of Sciences 113, n. 25 (13 giugno 2016): 6991–96. http://dx.doi.org/10.1073/pnas.1607584113.
Testo completoAbstract (sommario):
Ion channels regulate ion flow by opening and closing their pore gates. K+ channels commonly possess two pore gates, one at the intracellular end for fast channel activation/deactivation and the other at the selectivity filter for slow C-type inactivation/recovery. The large-conductance calcium-activated potassium (BK) channel lacks a classic intracellular bundle-crossing activation gate and normally show no C-type inactivation. We hypothesized that the BK channel’s activation gate may spatially overlap or coexist with the C-type inactivation gate at or near the selectivity filter. We induced C-type inactivation in BK channels and studied the relationship between activation/deactivation and C-type inactivation/recovery. We observed prominent slow C-type inactivation/recovery in BK channels by an extreme low concentration of extracellular K+ together with a Y294E/K/Q/S or Y279F mutation whose equivalent in Shaker channels (T449E/K/D/Q/S or W434F) caused a greatly accelerated rate of C-type inactivation or constitutive C-inactivation. C-type inactivation in most K+ channels occurs upon sustained membrane depolarization or channel opening and then recovers during hyperpolarized membrane potentials or channel closure. However, we found that the BK channel C-type inactivation occurred during hyperpolarized membrane potentials or with decreased intracellular calcium ([Ca2+]i) and recovered with depolarized membrane potentials or elevated [Ca2+]i. Constitutively open mutation prevented BK channels from C-type inactivation. We concluded that BK channel C-type inactivation is closed state-dependent and that its extents and rates inversely correlate with channel-open probability. Because C-type inactivation can involve multiple conformational changes at the selectivity filter, we propose that the BK channel’s normal closing may represent an early conformational stage of C-type inactivation.
39
Yarotskyy, Viktor, Guofeng Gao, Blaise Z. Peterson e Keith S. Elmslie. "Domain III regulates N-type (CaV2.2) calcium channel closing kinetics". Journal of Neurophysiology 107, n. 7 (1 aprile 2012): 1942–51. http://dx.doi.org/10.1152/jn.00993.2011.
Testo completoAbstract (sommario):
CaV2.2 (N-type) and CaV1.2 (L-type) calcium channels gate differently in response to membrane depolarization, which is critical to the unique physiological functions mediated by these channels. We wondered if the source for these differences could be identified. As a first step, we examined the effect of domain exchange between N-type and L-type channels on activation-deactivation kinetics, which were significantly different between these channels. Kinetic analysis of chimeric channels revealed N-channel-like deactivation for all chimeric channels containing N-channel domain III, while activation appeared to be a more distributed function across domains. This led us to hypothesize that domain III was an important regulator of N-channel closing. This idea was further examined with R-roscovitine, which is a trisubstituted purine that slows N-channel deactivation by exclusively binding to activated N-channels. L-channels lack this response to roscovitine, which allowed us to use N-L chimeras to test the role of domain III in roscovitine modulation of N-channel deactivation. In support of our hypothesis, all chimeric channels containing the N-channel domain III responded to roscovitine with slowed deactivation, while those chimeric channels with L-channel domain III did not. Thus a combination of kinetic and pharmacological evidence supports the hypothesis that domain III is an important regulator of N-channel closing. Our results support specialization of gating functions among calcium channel domains.
40
Dolphin, Annette C. "Voltage-gated calcium channels: Their discovery, function and importance as drug targets". Brain and Neuroscience Advances 2 (gennaio 2018): 239821281879480. http://dx.doi.org/10.1177/2398212818794805.
Testo completoAbstract (sommario):
This review will first describe the importance of Ca2+ entry for function of excitable cells, and the subsequent discovery of voltage-activated calcium conductances in these cells. This finding was rapidly followed by the identification of multiple subtypes of calcium conductance in different tissues. These were initially termed low- and high-voltage activated currents, but were then further subdivided into L-, N-, PQ-, R- and T-type calcium currents on the basis of differing pharmacology, voltage-dependent and kinetic properties, and single channel conductance. Purification of skeletal muscle calcium channels allowed the molecular identification of the pore-forming and auxiliary α2δ, β and ϒ subunits present in these calcium channel complexes. These advances then led to the cloning of the different subunits, which permitted molecular characterisation, to match the cloned channels with physiological function. Studies with knockout and other mutant mice then allowed further investigation of physiological and pathophysiological roles of calcium channels. In terms of pharmacology, cardiovascular L-type channels are targets for the widely used antihypertensive 1,4-dihydropyridines and other calcium channel blockers, N-type channels are a drug target in pain, and α2δ-1 is the therapeutic target of the gabapentinoid drugs, used in neuropathic pain. Recent structural advances have allowed a deeper understanding of Ca2+ permeation through the channel pore and the structure of both the pore-forming and auxiliary subunits. Voltage-gated calcium channels are subject to multiple pathways of modulation by G-protein and second messenger regulation. Furthermore, their trafficking pathways, subcellular localisation and functional specificity are the subjects of active investigation.
41
Yang, Tingting, Min He, Hailiang Zhang, Paula Q. Barrett e Changlong Hu. "L- and T-type calcium channels control aldosterone production from human adrenals". Journal of Endocrinology 244, n. 1 (gennaio 2020): 237–47. http://dx.doi.org/10.1530/joe-19-0259.
Testo completoAbstract (sommario):
Aldosterone, which plays a key role in the regulation of blood pressure, is produced by zona glomerulosa (ZG) cells of the adrenal cortex. Exaggerated overproduction of aldosterone from ZG cells causes primary hyperaldosteronism. In ZG cells, calcium entry through voltage-gated calcium channels plays a central role in the regulation of aldosterone secretion. Previous studies in animal adrenals and human adrenal adrenocortical cell lines suggest that the T-type but not the L-type calcium channel activity drives aldosterone production. However, recent clinical studies show that somatic mutations in L-type calcium channels are the second most prevalent cause of aldosterone-producing adenoma. Our objective was to define the roles of T and L-type calcium channels in regulating aldosterone secretion from human adrenals. We find that human adrenal ZG cells mainly express T-type CaV3.2/3.3 and L-type CaV1.2/1.3 calcium channels. TTA-P2, a specific inhibitor of T-type calcium channel subtypes, reduced basal aldosterone secretion from acutely prepared slices of human adrenals. Surprisingly, nifedipine, the prototypic inhibitor of L-type calcium channels, also decreased basal aldosterone secretion, suggesting that L-type calcium channels are active under basal conditions. In addition, TTA-P2 or nifedipine also inhibited aldosterone secretion stimulated by angiotensin II- or elevations in extracellular K+. Remarkably, blockade of either L- or T-type calcium channels inhibits basal and stimulated aldosterone production to a similar extent. Low concentrations of TTA-P2 and nifedipine showed additive inhibitory effect on aldosterone secretion. We conclude that T- and L-type calcium channels play equally important roles in controlling aldosterone production from human adrenals.
42
Chen, Nanjun, e Qigeng Fang. "Review the Regulation of Plasma Membrane Calcium Channel in Cancer and Patch Clamp Technique". E3S Web of Conferences 271 (2021): 04037. http://dx.doi.org/10.1051/e3sconf/202127104037.
Testo completoAbstract (sommario):
As one of the most versatile and universal second messengers, calcium plays an essential role in cell life. Here we briefly reviewed the research progress of how different calcium channels are located at the cell plasma membrane, including voltage-gated calcium channels (VGCCs), receptor-operated channels (ROC), and store-operated channels (ROC). These channels can regulate different cancer progression. Afterward, the patch clamp technique's development and operating principle, an important quantitative method used for ion channel investigation, are introduced in this paper.
43
Wang, Dan, Lotten Ragnarsson e Richard J. Lewis. "T-type Calcium Channels in Health and Disease". Current Medicinal Chemistry 27, n. 19 (4 giugno 2020): 3098–122. http://dx.doi.org/10.2174/0929867325666181001112821.
Testo completoAbstract (sommario):
Low Voltage-Activated (LVA) T-type calcium channels are characterized by transient current and Low Threshold Spikes (LTS) that trigger neuronal firing and oscillatory behavior. Combined with their preferential localization in dendrites and their specific “window current”, T-type calcium channels are considered to be key players in signal amplification and synaptic integration. Assisted by the emerging pharmacological tools, the structural determinants of channel gating and kinetics, as well as novel physiological and pathological functions of T-type calcium channels, are being uncovered. In this review, we provide an overview of structural determinants in T-type calcium channels, their involvement in disorders and diseases, the development of novel channel modulators, as well as Structure-Activity Relationship (SAR) studies that lead to rational drug design.
44
Bull, R., e J. J. Marengo. "Calcium-dependent halothane activation of sarcoplasmic reticulum calcium channels from frog skeletal muscle". American Journal of Physiology-Cell Physiology 266, n. 2 (1 febbraio 1994): C391—C396. http://dx.doi.org/10.1152/ajpcell.1994.266.2.c391.
Testo completoAbstract (sommario):
The effect of halothane on calcium channels present in sarcoplasmic reticulum membranes isolated from frog skeletal muscle was studied at the single channel level after fusing the isolated vesicles into planar lipid bilayers. Addition of 91 microM halothane to the cytosolic compartment containing 1 microM free calcium activated the channel by increasing fractional open time from 0.11 to 0.59, without changing the channel conductance. The activation of the channels by halothane was calcium dependent. At resting calcium concentrations in the cytosolic compartment, halothane failed to activate the channel, whereas maximal activation was found at 10 microM calcium. The free energy of halothane binding to the channel decreased from -5.8 kcal/mol at 1 microM calcium to -6.6 kcal/mol at 10 microM calcium. Halothane increased the open time constants and decreased the closed time constants, indicating that it binds to both the open and the closed configurations of the channel.
45
Shah, Kajol, Sarah Seeley, Castin Schulz, Jacqueline Fisher e Shubha Gururaja Rao. "Calcium Channels in the Heart: Disease States and Drugs". Cells 11, n. 6 (10 marzo 2022): 943. http://dx.doi.org/10.3390/cells11060943.
Testo completoAbstract (sommario):
Calcium ions are the major signaling ions in the cells. They regulate muscle contraction, neurotransmitter secretion, cell growth and migration, and the activity of several proteins including enzymes and ion channels and transporters. They participate in various signal transduction pathways, thereby regulating major physiological functions. Calcium ion entry into the cells is regulated by specific calcium channels and transporters. There are mainly six types of calcium channels, of which only two are prominent in the heart. In cardiac tissues, the two types of calcium channels are the L type and the T type. L-type channels are found in all cardiac cells and T-type are expressed in Purkinje cells, pacemaker and atrial cells. Both these types of channels contribute to atrioventricular conduction as well as pacemaker activity. Given the crucial role of calcium channels in the cardiac conduction system, mutations and dysfunctions of these channels are known to cause several diseases and disorders. Drugs targeting calcium channels hence are used in a wide variety of cardiac disorders including but not limited to hypertension, angina, and arrhythmias. This review summarizes the type of cardiac calcium channels, their function, and disorders caused by their mutations and dysfunctions. Finally, this review also focuses on the types of calcium channel blockers and their use in a variety of cardiac disorders.
46
Wang, Jijiang, Mustapha Irnaten e David Mendelowitz. "Agatoxin-IVA-Sensitive Calcium Channels Mediate the Presynaptic and Postsynaptic Nicotinic Activation of Cardiac Vagal Neurons". Journal of Neurophysiology 85, n. 1 (1 gennaio 2001): 164–68. http://dx.doi.org/10.1152/jn.2001.85.1.164.
Testo completoAbstract (sommario):
Whole cell currents and miniature glutamatergic synaptic events (minis) were recorded in vitro from cardiac vagal neurons in the nucleus ambiguus using the patch-clamp technique. We examined whether voltage-dependent calcium channels were involved in the nicotinic excitation of cardiac vagal neurons. Nicotine evoked an inward current, increase in mini amplitude, and increase in mini frequency in cardiac vagal neurons. These responses were inhibited by the nonselective voltage-dependent calcium channel blocker Cd (100 μM). The P-type voltage-dependent calcium channel blocker agatoxin IVA (100 nM) abolished the nicotine-evoked responses. Nimodipine (2 μM), an antagonist of L-type calcium channels, inhibited the increase in mini amplitude and frequency but did not block the ligand gated inward current. The N- and Q-type voltage-dependent calcium channel antagonists conotoxin GVIA (1 μM) and conotoxin MVIIC (5 μM) had no effect. We conclude that the presynaptic and postsynaptic facilitation of glutamatergic neurotransmission to cardiac vagal neurons by nicotine involves activation of agatoxin-IVA-sensitive and possibly L-type voltage-dependent calcium channels. The postsynaptic inward current elicited by nicotine is dependent on activation of agatoxin-IVA-sensitive voltage-dependent calcium channels.
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Büschges, A., M. A. Wikström, S. Grillner e A. El Manira. "Roles of High-Voltage–Activated Calcium Channel Subtypes in a Vertebrate Spinal Locomotor Network". Journal of Neurophysiology 84, n. 6 (1 dicembre 2000): 2758–66. http://dx.doi.org/10.1152/jn.2000.84.6.2758.
Testo completoAbstract (sommario):
Lamprey spinal cord neurons possess N-, L-, and P/Q-type high-voltage–activated (HVA) calcium channels. We have analyzed the role of the different HVA calcium channels subtypes in the overall functioning of the spinal locomotor network by monitoring the influence of their specific agonists and antagonists on synaptic transmission and on N-methyl-d-aspartate (NMDA)–elicited fictive locomotion. The N-type calcium channel blocker ω-conotoxin GVIA (ω-CgTx) depressed synaptic transmission from excitatory and inhibitory interneurons. Blocking L-type and P/Q-type calcium channels with nimodipine and ω-agatoxin, respectively, did not affect synaptic transmission. Application of ω-CgTx initially decreased the frequency of the locomotor rhythm, increased the burst duration, and subsequently increased the coefficient of variation and disrupted the motor pattern. These effects were accompanied by a depression of the synaptic drive between neurons in the locomotor network. Blockade of L-type channels by nimodipine also decreased the frequency and increased the duration of the locomotor bursts. Conversely, potentiation of L-type channels increased the frequency of the locomotor activity and decreased the duration of the ventral root bursts. In contrast to blockade of N-type channels, blockade or potentiation of L-type calcium channels had no effect on the stability of the locomotor pattern. The P/Q-type calcium channel blocker ω-agatoxin IVA had little effect on the locomotor frequency or burst duration. The results indicate that rhythm generation in the spinal locomotor network of the lamprey relies on calcium influx through L-type and N-type calcium channels.
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Syamsunarno, Mas Rizky Anggun Adipurna, Alif Bagus Rakhimullah, Uni Gamayani, Masahiko Kurabayasi, Tatsuya Iso, Ratu Safitri e Ramdan Panigoro. "Iron Administration Affects Cardiac Calcium Channel Expression in Mice: The Role of Cardiac Calcium Channel Expression in The Heart of Iron Overload Mice Model". Indonesian Biomedical Journal 12, n. 3 (5 settembre 2020): 261–6. http://dx.doi.org/10.18585/inabj.v12i3.1170.
Testo completoAbstract (sommario):
BACKGROUND: Iron-overload cardiomyopathy (IOC) is a major comorbidity in patients with chronic repetitive blood transfusion due to myocardial iron uptake that facilitated by calcium channels. As cardiac compensatory mechanism to IOC, we hypothesized the cardiac calcium channels expression would be increased and involved in cardiomyopathy progressivity. This study was aimed to investigate the gene expression of calcium channels in the heart of the iron overload mice model.METHODS: Mice were divided into three groups according to iron administration doses 0, 0.1, and 0.3 mg/day. Systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) were measured for the representation of cardiovascular outcomes. The heart tissues were harvested. Further mRNA levels of L-type calcium channels (LTCCs) and T-type calcium channels (TTCCs) were examined using semi-quantitative PCR. The expressions of cardiac calcium channels and blood pressure among the three groups were compared.RESULTS: The expressions of TTCCs in the two iron-injected groups were higher than the control group (p=0.018). The expressions of LTCCs were not different (p=0.413) among groups. SBP, DBP, and MAP of the iron-injected group were lower than the control group (p=0.025, p=0.011, and p=0.008, respectively).CONCLUSION: Iron administration affects the expression of TTCCs but not the LTCCs, accompanied by decreasing of systolic and diastolic blood pressure.KEYWORDS: cardiomyopathy, iron overload, L-type calcium channel, T-type calcium channel.
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Rosa, Juliana M., Cristina J. Torregrosa-Hetland, Inés Colmena, Luis M. Gutiérrez, Antonio G. García e Luis Gandía. "Calcium entry through slow-inactivating L-type calcium channels preferentially triggers endocytosis rather than exocytosis in bovine chromaffin cells". American Journal of Physiology-Cell Physiology 301, n. 1 (luglio 2011): C86—C98. http://dx.doi.org/10.1152/ajpcell.00440.2010.
Testo completoAbstract (sommario):
Calcium (Ca2+)-dependent endocytosis has been linked to preferential Ca2+ entry through the L-type (α1D, CaV1.3) of voltage-dependent Ca2+ channels (VDCCs). Considering that the Ca2+-dependent exocytotic release of neurotransmitters is mostly triggered by Ca2+ entry through N-(α1B, CaV2.2) or PQ-VDCCs (α1A, CaV2.1) and that exocytosis and endocytosis are coupled, the supposition that the different channel subtypes are specialized to control different cell functions is attractive. Here we have explored this hypothesis in primary cultures of bovine adrenal chromaffin cells where PQ channels account for 50% of Ca2+ current ( ICa), 30% for N channels, and 20% for L channels. We used patch-clamp and fluorescence techniques to measure the exo-endocytotic responses triggered by long depolarizing stimuli, in 1, 2, or 10 mM concentrations of extracellular Ca2+ ([Ca2+]e). Exo-endocytotic responses were little affected by ω-conotoxin GVIA (N channel blocker), whereas ω-agatoxin IVA (PQ channel blocker) caused 80% blockade of exocytosis as well as endocytosis. In contrast, nifedipine (L channel blocker) only caused 20% inhibition of exocytosis but as much as 90% inhibition of endocytosis. Conversely, FPL67146 (an activator of L VDCCs) notably augmented endocytosis. Photoreleased caged Ca2+ caused substantially smaller endocytotic responses compared with those produced by K+ depolarization. Using fluorescence antibodies, no colocalization between L, N, or PQ channels with clathrin was found; a 20–30% colocalization was found between dynamin and all three channel antibodies. This is incompatible with the view that L channels are coupled to the endocytotic machine. Data rather support a mechanism implying the different inactivation rates of L (slow-inactivating) and N/PQ channels (fast-inactivating). Thus a slow but more sustained Ca2+ entry through L channels could be a requirement to trigger endocytosis efficiently, at least in bovine chromaffin cells.
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Nunoki, K., V. Florio e W. A. Catterall. "Activation of purified calcium channels by stoichiometric protein phosphorylation". Proceedings of the National Academy of Sciences 86, n. 17 (settembre 1989): 6816–20. http://dx.doi.org/10.1073/pnas.86.17.6816.
Testo completoAbstract (sommario):
Purified dihydropyridine-sensitive calcium channels from rabbit skeletal muscle were reconstituted into phosphatidylcholine vesicles to evaluate the effect of phosphorylation by cyclic AMP-dependent protein kinase (PK-A) on their function. Both the rate and extent of 45Ca2+ uptake into vesicles containing reconstituted calcium channels were increased severalfold after incubation with ATP and PK-A. The degree of stimulation of 45Ca2+ uptake was linearly proportional to the extent of phosphorylation of the alpha 1 and beta subunits of the calcium channel up to a stoichiometry of approximately 1 mol of phosphate incorporated into each subunit. The calcium channels activated by phosphorylation were determined to be incorporated into the reconstituted vesicles in the inside-out orientation and were completely inhibited by low concentrations of dihydropyridines, phenylalkylamines, Cd2+, Ni2+, and Mg2+. The results demonstrate a direct relationship between PK-A-catalyzed phosphorylation of the alpha 1 and beta subunits of the purified calcium channel and activation of the ion conductance activity of the dihydropyridine-sensitive calcium channels.