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Journal articles on the topic 'Conductance'
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1
Senior, A., M. J. Kosch, and F. Honary. "Comparison of methods to determine auroral ionospheric conductances using ground-based optical and riometer data." Annales Geophysicae 26, no. 12 (December 2, 2008): 3831–40. http://dx.doi.org/10.5194/angeo-26-3831-2008.
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Abstract. Ground-based images of auroral optical emissions and cosmic radio noise absorption provide information on particle precipitation which enhances ionospheric conductances. Knowledge of this conductance field is important to understand the current systems associated with auroral features. Three methods of using ground-based optical and riometer data to estimate ionospheric conductances in the aurora are compared to conductances derived from incoherent scatter radar measurements. It is shown that a method using the 557.7 nm emission intensity alone gives the best results for the Pedersen conductance whilst a method using both this intensity and cosmic noise absorption is best for the Hall conductance. A method using cosmic noise absorption alone gives reasonable performance for the Hall conductance and the Hall/Pedersen conductance ratio, but performs poorly for the Pedersen conductance. It also appears to underestimate the Hall conductance significantly during times when softer precipitation is present, for example in discrete auroral arcs. There is some indication that the methods do not degrade noticeably for angles up to ~20° off magnetic zenith.
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Butt, A. G., W. L. Clapp, and R. A. Frizzell. "Potassium conductances in tracheal epithelium activated by secretion and cell swelling." American Journal of Physiology-Cell Physiology 258, no. 4 (April 1, 1990): C630—C638. http://dx.doi.org/10.1152/ajpcell.1990.258.4.c630.
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Increased basolateral membrane K conductance accompanies stimulation of Cl secretion across canine trachea. To assess the K conductance properties, we permeabilized the apical membranes with amphotericin B and monitored the current and conductance caused by K flow across the basolateral membranes. Under basal unstimulated conditions, two K conductances could be distinguished by blockers. One was inhibited only by barium; the other was sensitive also to quinidine and lidocaine. The permeabilities of the basal conductance pathways to K and Rb were similar (PK/PRb approximately equal to 1.5). The secretory agonist, epinephrine, selectively increased the quinidine-insensitive conductance, implicating it in the Cl secretory response. Cell swelling induced a third conductance with a low permeability to Rb (PK/PRb approximately equal to 10) that was quinidine sensitive. In tissues not treated with amphotericin, neither quinidine nor Rb-for-K replacement inhibited transepithelial Cl secretion. Thus neither of the quinidine-sensitive K conductances (basal or swelling induced) contribute to the increase in basolateral K conductance during Cl secretion. Cell shrinkage inhibited all three conductances and secretion, suggesting that the initial priority of the cell is volume regulation.
3
Yoshii, K., L. E. Moore, and B. N. Christensen. "Effect of subthreshold voltage-dependent conductances on the transfer function of branched excitable cells and the conduction of synaptic potentials." Journal of Neurophysiology 59, no. 3 (March 1, 1988): 706–16. http://dx.doi.org/10.1152/jn.1988.59.3.706.
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1. Impulse response functions were determined from complex point impedance and transfer functions from cultured NG-108 cells to simulate the propagation of a synaptic potential in response to the release of transmitter. In general, the flow of synaptic current has a much shorter duration than the normal membrane time constant, thereby making the use of impulse response functions useful approximations to synaptic events. 2. The resonance observed during the activation of the potassium conductance was reflected in the impulse response function as a pronounced damped oscillation. A comparison of the impulse response functions calculated from point impedance and transfer functions showed similar results for current injections in the growth cone. 3. In addition to the resonance effects of the voltage-dependent conductances on transfer and impulse response functions due principally to the activation of conductances for outward currents, transfer functions were measured during the activation of a steady-state negative conductance. Under these conditions the phase function approaches 180 degrees, indicating that the voltage response is out of phase with the current. 4. In the steady state, the effect of a negative conductance is to algebraically add to the positive conductances and generally decrease the absolute conductance unless there is a net negative current. The decreased conductance enhances the impulse response and the DC space constant, thus leading to a better propagation of slow potentials. This effect can be seen as a decrease in the electrotonic length, L, with intermediate depolarizations. At large depolarizations the steady-state activation of the K conductance generally dominates and leads to a greatly increased electrotonic length. 5. Both the net conductances and the associated kinetics play a role in shaping the potential changes during a synaptic current. This is especially critical if there is a net negative steady-state conductance. Under these conditions there is a surprising reduction in the impulse response function. 6. Thus, during a subthreshold activation of the voltage-dependent negative conductances, the observable synaptic potentials would be either large potential responses due to an apparent increase in the impedance (algebraic summation of positive and negative conductances with a net positive conductance) or a minimal response because of the phasic cancellation due to a net negative conductance. The latter condition could exist near the synaptic reversal potential due to a large synaptic drive and would appear experimentally as a form of inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)
4
Monje, Oscar, and Bruce Bugbee. "Radiometric Method for Determining Canopy Stomatal Conductance in Controlled Environments." Agronomy 9, no. 3 (February 27, 2019): 114. http://dx.doi.org/10.3390/agronomy9030114.
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Canopy stomatal conductance is a key physiological factor controlling transpiration from plant canopies, but it is extremely difficult to determine in field environments. The objective of this study was to develop a radiometric method for calculating canopy stomatal conductance for two plant species—wheat and soybean from direct measurements of bulk surface conductance to water vapor and the canopy aerodynamic conductance in controlled-environment chambers. The chamber provides constant net radiation, temperature, humidity, and ventilation rate to the plant canopy. In this method, stepwise changes in chamber CO2 alter canopy temperature, latent heat, and sensible heat fluxes simultaneously. Sensible heat and the radiometric canopy-to-air temperature difference are computed from direct measurements of net radiation, canopy transpiration, photosynthesis, radiometric temperature, and air temperature. The canopy aerodynamic conductance to the transfer of water vapor is then determined from a plot of sensible heat versus radiometric canopy-to-air temperature difference. Finally, canopy stomatal conductance is calculated from canopy surface and aerodynamic conductances. The canopy aerodynamic conductance was 5.5 mol m−2 s−1 in wheat and 2.5 mol m−2 s−1 in soybean canopies. At 400 umol mol−1 of CO2 and 86 kPa atmospheric pressure, canopy stomatal conductances were 2.1 mol m−2 s−1 for wheat and 1.1 mol m−2 s−1 for soybean, comparable to canopy stomatal conductances reported in field studies. This method measures canopy aerodynamic conductance in controlled-environment chambers where the log-wind profile approximation does not apply and provides an improved technique for measuring canopy-level responses of canopy stomatal conductance and the decoupling coefficient. The method was used to determine the response of canopy stomatal conductance to increased CO2 concentration and to determine the sensitivity of canopy transpiration to changes in canopy stomatal conductance. These responses are useful for improving the prediction of ecosystem-level water fluxes in response to climatic variables.
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Apelblat, Alexander, and Josef Barthel. "Conductance Studies of Aqueous Succinic Acid." Zeitschrift für Naturforschung A 47, no. 3 (March 1, 1992): 493–98. http://dx.doi.org/10.1515/zna-1992-0309.
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Abstract Conductance measurements of aqueous solutions of succinic acid and of di-sodium succinate were performed from 278.15 to 308.15 K and the limiting conductances λ0 (1/2 Succ2- ) are reported. The Waiden product is independent of temperature: λ0(1/2 Succ2-)*η(T) = 0.503 ± 0.001. The salt conductances closely obey the Onsager limiting law. The evaluation of the equilibrium constants for the primary and secondary steps of dissociation, K1 and K2, and the limiting conductances of the hydrosuccinate ion, λ0(HSucc-), are discussed using the Quint and Viallard conductance equation
6
Carter, Gregory A., and Alan H. Teramura. "Nonsummer stomatal conductance for the invasive vines kudzu and Japanese honeysuckle." Canadian Journal of Botany 66, no. 12 (December 1, 1988): 2392–95. http://dx.doi.org/10.1139/b88-325.
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A field study was conducted in Maryland to estimate nonsummer stomatal conductances on clear days for two invasive woody vine species common to the southeastern United States. Before the first frost in late October, stomatal conductances were similar for kudzu (Pueraria lobata) and Japanese honeysuckle (Lonicera japonica). When minimum predawn air temperature fell to −0.6 °C, kudzu leaves were irreversibly damaged, whereas maximum daily conductance in honeysuckle was unaffected. Maximum conductances in honeysuckle increased to 14 mm s−1 in late November and mid-December, similar to late-spring and summer values. When minimum air temperatures decreased to −2.8 °C in January, conductance still remained above 5 mm s−1. Maximum daily conductance was lowest in early March, corresponding with low leaf temperatures. By mid-April, maximum conductance increased to 10 mm s−1. Conductances suggested that rates of leaf gas exchange in honeysuckle during fall, winter, and spring were relatively high. Carbon gain during this period might thus contribute substantially to the invasive growth characteristic of the species.
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Munger, Philip H., James M. Chandler, and J. Tom Cothren. "Effect of Water Stress on Photosynthetic Parameters of Soybean (Glycine max) and Velvetleaf (Abutilon theophrasti)." Weed Science 35, no. 1 (January 1987): 15–21. http://dx.doi.org/10.1017/s0043174500026722.
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Greenhouse experiments were conducted to elucidate the effects of water stress on photosynthetic parameters of soybean [Glycine max(L.) Merr. ‘Hutton′] and velvetleaf (Abutilon theophrastiMedik. # ABUTH). Stomatal conductance of both species responded curvilinearly to reductions in leaf water potential. At leaf water potentials less negative than −2.5 MPa, stomatal conductance, net photosynthetic rate, and transpiration rate were greater in velvetleaf than in soybean. Soybean photosynthetic rate was linearly related to stomatal conductance. Velvetleaf photosynthetic rate increased linearly with stomatal conductances up to 1.5 cm s–1; however, no increase in photosynthetic rate was observed at stomatal conductances greater than 1.5 cm s–1, indicating nonstomatal limitations to photosynthesis. As water stress intensified, stomatal conductance, photosynthetic rate, and transpiration of velvetleaf declined more rapidly than in soybean.
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Skryma, R., N. Prevarskaya, P. Vacher, and B. Dufy. "Voltage-dependent ionic conductances in Chinese hamster ovary cells." American Journal of Physiology-Cell Physiology 267, no. 2 (August 1, 1994): C544—C553. http://dx.doi.org/10.1152/ajpcell.1994.267.2.c544.
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Chinese hamster ovary (CHO) cells are becoming a widely used biological material. A number of studies report membrane ion conductance changes after transfection of channels and receptors, but there are few data available on the properties of membrane ion conductances of CHO cells before transfection. In this work we studied voltage-dependent ionic conductances in cultures of CHO native (CHO-K1) cells. Three types of voltage-dependent ionic conductances were identified: 1) a K+ conductance showing sensitivity to Ca2+ and a unit conductance of approximately 210 pS in symmetrical 150 mM K+ outside-out patches (this conductance, which did not inactivate during a 160-ms pulse, was inhibited by 30 nM charybdotoxin but not by 30 mM extracellular tetraethylammonium); 2) a rapidly activating and inactivating tetrodotoxin (TTX)-sensitive inward current, peaking at about -10 to 0 mV (this current showed characteristics similar in many respects to Na+ current recorded in neurons); and 3) another voltage-dependent inward current, which had slow inactivation, was TTX insensitive but was blocked by Co2+ (current was also carried by Ba2+, peaked at approximately 0 to +10 mV, was identified as a Ca2+ conductance, and was inhibited by dihydropyridines but not by 10 microM omega-conotoxin). Cell-attached patch recordings of single Ca2+ channel currents demonstrated a unitary conductance of approximately 20 pS.
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Pospischil, Martin, Zuzanna Piwkowska, Michelle Rudolph, Thierry Bal, and Alain Destexhe. "Calculating Event-Triggered Average Synaptic Conductances From the Membrane Potential." Journal of Neurophysiology 97, no. 3 (March 2007): 2544–52. http://dx.doi.org/10.1152/jn.01000.2006.
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The optimal patterns of synaptic conductances for spike generation in central neurons is a subject of considerable interest. Ideally such conductance time courses should be extracted from membrane potential ( Vm) activity, but this is difficult because the nonlinear contribution of conductances to the Vm renders their estimation from the membrane equation extremely sensitive. We outline here a solution to this problem based on a discretization of the time axis. This procedure can extract the time course of excitatory and inhibitory conductances solely from the analysis of Vm activity. We test this method by calculating spike-triggered averages of synaptic conductances using numerical simulations of the integrate-and-fire model subject to colored conductance noise. The procedure was also tested successfully in biological cortical neurons using conductance noise injected with dynamic clamp. This method should allow the extraction of synaptic conductances from Vm recordings in vivo.
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Palmer, Lawrence G., and Gustavo Frindt. "Cl− channels of the distal nephron." American Journal of Physiology-Renal Physiology 291, no. 6 (December 2006): F1157—F1168. http://dx.doi.org/10.1152/ajprenal.00496.2005.
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Cl− currents were observed under whole cell clamp conditions in cells of the rat cortical collecting duct (CCD), connecting tubule (CNT), and thick ascending limb of Henle's loop (TALH). These currents were much larger in intercalated cells compared with principal cells of the CCD and were also larger in the TALH and in the CNT compared with the CCD. The conductance had no strong voltage dependence, and steady-state currents were similar in inward and outward directions with similar Cl− concentrations on both sides of the membrane. Current transients were observed, particularly at low Cl− concentrations, which could be explained by solute depletion and concentration in fluid layers next to the membrane. The currents had a remarkable selectivity among anions. Among halides, Br− and F− conductances were only 15% of that of Cl−, and I− conductance was immeasurably small. SCN− and OCN− conductances were ∼50%, and aspartate, glutamate, and methanesulfonate conductance was ∼5% that of Cl−. No conductance could be measured for any other anion tested, including NO3−, HCO3−, formate, acetate, or isethionate; NO3− and I− appeared to block the channels weakly. Conductances were diminished by lowering the extracellular pH to 6.4. The properties of the conductance fit best with those of the cloned renal anion channel ClC-K2 and likely reflect the basolateral Cl− conductances of the cells of these nephron segments.
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Melikyan, G. B., W. D. Niles, V. A. Ratinov, M. Karhanek, J. Zimmerberg, and F. S. Cohen. "Comparison of transient and successful fusion pores connecting influenza hemagglutinin expressing cells to planar membranes." Journal of General Physiology 106, no. 5 (November 1, 1995): 803–19. http://dx.doi.org/10.1085/jgp.106.5.803.
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Time-resolved admittance measurements were used to investigate the evolution of fusion pores formed between cells expressing influenza virus hemagglutinin (HA) and planar bilayer membranes. The majority of fusion pores opened in a stepwise fashion to semistable conductance levels of several nS. About 20% of the pores had measurable rise times to nS conductances; some of these opened to conductances of approximately 500 pS where they briefly lingered before opening further to semistable conductances. The fall times of closing were statistically similar to the rise times of opening. All fusion pores exhibited semistable values of conductance, varying from approximately 2-20 nS; they would then either close or fully open to conductances on the order of 1 microS. The majority of pores closed; approximately 10% fully opened. Once within the semistable stage, all fusion pores, even those that eventually closed, tended to grow. Statistically, however, before closing, transient fusion pores ceased to grow and reversed their conductance pattern: conductances decreased with a measurable time course until a final drop to closure. In contrast, pore enlargement to the fully open state tended to occur from the largest conductance values attained during a pore's semistable stage. This final enlargement was characterized by a stepwise increase in conductance. The density of HA on the cell surface did not strongly affect pore dynamics. But increased proteolytic treatment of cell surfaces did lead to faster growth within the semistable range. Transient pores and pores that fully opened had indistinguishable initial conductances and statistically identical time courses of early growth, suggesting they were the same upon formation. We suggest that transient and fully open pores evolved from common structures with stochastic factors determining their fate.
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Britton, Oliver J., and Blanca Rodriguez. "A population of in silico models identifies the interplay between Nav 1.8 conductance and potassium currents as key in regulating human dorsal root ganglion neuron excitability." F1000Research 11 (January 27, 2022): 104. http://dx.doi.org/10.12688/f1000research.74551.1.
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Background: The Nav 1.8 sodium channel has a key role in generating repetitive action potentials in nociceptive human dorsal root ganglion neurons. Nav 1.8 is differentiated from other voltage-gated sodium channels by its unusually slow inactivation kinetics and depolarised voltage-dependence of activation. These features are particularly pronounced in the human Nav 1.8 channel and allow the channel to remain active during repolarisation. Gain-of-function mutations in Nav 1.8 have been linked to neuropathic pain and selective blockers of Nav 1.8 have been developed as potential new analgesics. However, it is not well understood how modulating the Nav 1.8 conductance alters neuronal excitability and how this depends on the balance of other ion channels expressed by nociceptive neurons. Methods: To investigate this, we developed a novel computational model of the human dorsal root ganglion neuron and used it to construct a population of models that mimicked inter-neuronal heterogeneity in ionic conductances and action potential morphology Results: By simulating changes to the Nav 1.8 conductance in the population of models, we found that moderately increasing the Nav 1.8 conductance led to increased firing rate, as expected, but increasing Nav 1.8 conductance beyond an inflection point caused firing rate to decrease. We found that the delayed rectifier and M-type potassium conductances were also critical for determining neuronal excitability. In particular, altering the delayed rectifier potassium conductance shifted the position of the Nav 1.8 inflection point and therefore the relationship between Nav 1.8 conductance and firing rate. Conclusions: Our results suggest that the effects of modulating Nav 1.8 in a nociceptive neuron can depend significantly on other conductances, particularly potassium conductances.
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Maltenfort, Mitchell G., Carrie A. Phillips, Martha L. McCurdy, and Thomas M. Hamm. "Determination of the Location and Magnitude of Synaptic Conductance Changes in Spinal Motoneurons by Impedance Measurements." Journal of Neurophysiology 92, no. 3 (September 2004): 1400–1416. http://dx.doi.org/10.1152/jn.00873.2003.
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The relation between impedance change and the location and magnitude of a tonic synaptic conductance was examined in compartmental motoneuron models based on previously published data. The dependency of motoneuron impedance on system time constant (τ), electrotonic length (L), and dendritic-to-somatic conductance ratio (ρ) was examined, showing that the relation between impedance phase and ρ differed markedly between models with uniform and nonuniform membrane resistivity. Dendritic synaptic conductances decreased impedance magnitude at low frequencies; at higher frequencies, impedance magnitude increased. The frequency at which the change in impedance magnitude reversed from a decrease to an increase—the reversal frequency, Fr—was a good estimator of electrotonic synaptic location. A measure of the average normalized impedance change at frequencies less than Fr, cuΔZ, estimated relative synaptic conductance. Fr and cuΔZ provided useful estimates of synaptic location and conductance in models with nonuniform (step, sigmoidal) and uniform membrane resistivity. Fr also provided good estimates of spatial synaptic location on the equivalent cable in both step and sigmoidal models. Variability in relations between Fr, cuΔZ, and conductance location and magnitude between neurons was reduced by normalization with ρ and τ. The effects on Fr and cuΔZ of noise in experimental recordings, different synaptic distributions, and voltage-dependent conductances were also assessed. This study indicates that location and conductance of tonic dendritic conductances can be estimated from Fr, cuΔZ, and basic electrotonic motoneuron parameters with the exercise of suitable precautions.
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Quadroni, R., and T. Knopfel. "Compartmental models of type A and type B guinea pig medial vestibular neurons." Journal of Neurophysiology 72, no. 4 (October 1, 1994): 1911–24. http://dx.doi.org/10.1152/jn.1994.72.4.1911.
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1. We have developed compartmental models of guinea-pig medial vestibular nuclei neurons (MVNns). The structure and the parameters of the model cells were chosen to reproduce the responses of type A and type B MVNns as described in electrophysiological recordings. 2. Dynamics of membrane potentials were modeled in 46 and 61 branched electrical compartments for Type A and Type B MVNns, respectively. Each compartment was allowed to contain up to nine active ionic conductances: a fast inactivating sodium conductance, gNa, a persistent sodium conductance, gNap, a low-voltage activated calcium conductance, gCa(LVA), a high-voltage activated calcium conductance, gCa(HVA), a fast-voltage activated potassium conductance, gK(fast), a slowly relaxing voltage activated potassium conductance, gK(slow), a fast transient potassium channel, gK(A), a slowly relaxing mixed sodium-potassium conductance activating at hyperpolarized membrane potentials, gH, and a calcium-activated potassium conductance gK(AHP). The kinetics of these conductances were derived from voltage-clamp studies in a variety of preparations. Kinetic parameters as well as distribution and density of ion channels were adjusted to yield the reported electrophysiological behavior of medial vestibular neurons. 3. Dynamics of intracellular free [Ca2]i were modeled by inclusion of a Ca(2+)-pump and a Na(+)-Ca2+ exchanger for extrusion of calcium. Diffusion of calcium between submembraneous sites and the center of an electrical compartment was modeled by 25 and 6 shell-like chemical compartments for the cell body and the proximal dendrites, respectively. These compartments also contained binding sites for calcium. 4. The dynamics of active conductances were the same in both models except for gK(fast). This was necessary to achieve the different shape of spikes and of spike afterhyperpolarization in type A and type B MVNns. An intermediate depolarizing component of the spike afterhyperpolarization of type B neurons in part depended on their dendritic cable structure. 5. Variation of the low threshold calcium conductance, gCa(LVA), shows that the ability to generate low-threshold spike bursts critically depends on the density of this conductance. Sodium plateaus were generated when increasing the density of gNap. 6. The type B model cell generated rhythmic bursts of spiking activity under simulation of two distinct experimental conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
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Kleene, S. J., R. C. Gesteland, and S. H. Bryant. "An electrophysiological survey of frog olfactory cilia." Journal of Experimental Biology 195, no. 1 (October 1, 1994): 307–28. http://dx.doi.org/10.1242/jeb.195.1.307.
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Individual olfactory receptor neurons vary widely in their responses to odorants. Olfactory stimulus reception occurs in the cilia of the receptor neurons. Thus, the variability among individual neurons could in part be due to differences among the olfactory cilia. We have quantified the known conductance properties of each of 117 frog olfactory cilia. From a strictly qualitative viewpoint, the cilia were very homogeneous. All but a few of them had a basal conductance in the absence of odorants and second messengers, conductances stimulated by cytoplasmic cyclic AMP and by Ca2+ and a conductance measured in the presence of ATP and stimulated by GTP gamma S. However, the magnitudes of the conductances varied widely among the cilia. Amplitudes of the cyclic-AMP- and Ca(2+)-activated ciliary currents correlated strongly with one another across the 117 cilia and 24 frogs studied, suggesting that expression of the underlying channels may be co-regulated. None of the conductance properties correlated strongly with ciliary length, a marker of cell maturity. Given cytoplasmic MgATP as substrate, ciliary adenylate cyclase apparently produced cyclic AMP, which in turn gated membrane channels and increased the ciliary conductance. In some cilia, MgATP alone caused a very large increase in conductance. In others, there was little effect unless GTP gamma S, which increases cyclase activity, was also added. No effect of cytoplasmic inositol trisphosphate on ciliary conductance was detectable.
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Frolov, Roman, Esa-Ville Immonen, and Matti Weckström. "Visual ecology and potassium conductances of insect photoreceptors." Journal of Neurophysiology 115, no. 4 (April 1, 2016): 2147–57. http://dx.doi.org/10.1152/jn.00795.2015.
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Voltage-activated potassium channels (Kv channels) in the microvillar photoreceptors of arthropods are responsible for repolarization and regulation of photoreceptor signaling bandwidth. On the basis of analyzing Kv channels in dipteran flies, it was suggested that diurnal, rapidly flying insects predominantly express sustained K+ conductances, whereas crepuscular and nocturnally active animals exhibit strongly inactivating Kv conductances. The latter was suggested to function for minimizing cellular energy consumption. In this study we further explore the evolutionary adaptations of the photoreceptor channelome to visual ecology and behavior by comparing K+ conductances in 15 phylogenetically diverse insects, using patch-clamp recordings from dissociated ommatidia. We show that rapid diurnal flyers such as the blowfly ( Calliphora vicina) and the honeybee ( Apis mellifera) express relatively large noninactivating Kv conductances, conforming to the earlier hypothesis in Diptera. Nocturnal and/or slow-moving species do not in general exhibit stronger Kv conductance inactivation in the physiological membrane voltage range, but the photoreceptors in species that are known to rely more on vision behaviorally had higher densities of sustained Kv conductances than photoreceptors of less visually guided species. No statistically significant trends related to visual performance could be identified for the rapidly inactivating Kv conductances. Counterintuitively, strong negative correlations were observed between photoreceptor capacitance and specific membrane conductance for both sustained and inactivating fractions of Kv conductance, suggesting insignificant evolutionary pressure to offset negative effects of high capacitance on membrane filtering with increased conductance.
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Golowasch, Jorge, Amitabha Bose, Yinzheng Guan, Dalia Salloum, Andrea Roeser, and Farzan Nadim. "A balance of outward and linear inward ionic currents is required for generation of slow-wave oscillations." Journal of Neurophysiology 118, no. 2 (August 1, 2017): 1092–104. http://dx.doi.org/10.1152/jn.00240.2017.
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Pacemaker neuron-generated rhythmic activity requires the activation of at least one inward and one outward current. We have previously shown that the inward current can be a linear current (with negative conductance). Using this simple mechanism, here we demonstrate that the inward current conductance must be in relative balance with the outward current conductances to generate oscillatory activity. Surprisingly, an excess of outward conductances completely precludes the possibility of achieving such a balance.
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Merlin, Didier, Lianwei Jiang, Gregg R. Strohmeier, Asma Nusrat, Seth L. Alper, Wayne I. Lencer, and James L. Madara. "Distinct Ca2+- and cAMP-dependent anion conductances in the apical membrane of polarized T84 cells." American Journal of Physiology-Cell Physiology 275, no. 2 (August 1, 1998): C484—C495. http://dx.doi.org/10.1152/ajpcell.1998.275.2.c484.
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Monolayers of the human colonic epithelial cell line T84 exhibit electrogenic Cl− secretion in response to the Ca2+ agonist thapsigargin and to the cAMP agonist forskolin. To evaluate directly the regulation of apical Cl−conductance by these two agonists, we have utilized amphotericin B to permeabilize selectively the basolateral membranes of T84 cell monolayers. We find that apical anion conductance is stimulated by both forskolin and thapsigargin but that these conductances are differentially sensitive to the anion channel blocker DIDS. DIDS inhibits thapsigargin-stimulated responses completely but forskolin responses only partially. Furthermore, the apical membrane anion conductances elicited by these two agonists differ in anion selectivity (for thapsigargin, I− > Cl−; for forskolin, Cl− > I−). However, the DIDS-sensitive component of the forskolin-induced conductance response exhibits anion selectivity similar to that induced by thapsigargin (I− > Cl−). Thus forskolin-induced apical anion conductance comprises at least two components, one of which has features in common with that elicited by thapsigargin.
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Endo, Toshiaki, and Ole Kiehn. "Asymmetric Operation of the Locomotor Central Pattern Generator in the Neonatal Mouse Spinal Cord." Journal of Neurophysiology 100, no. 6 (December 2008): 3043–54. http://dx.doi.org/10.1152/jn.90729.2008.
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The rhythmic voltage oscillations in motor neurons (MNs) during locomotor movements reflect the operation of the pre-MN central pattern generator (CPG) network. Recordings from MNs can thus be used as a method to deduct the organization of CPGs. Here, we use continuous conductance measurements and decomposition methods to quantitatively assess the weighting and phase tuning of synaptic inputs to different flexor and extensor MNs during locomotor-like activity in the isolated neonatal mice lumbar spinal cord preparation. Whole cell recordings were obtained from 22 flexor and 18 extensor MNs in rostral and caudal lumbar segments. In all flexor and the large majority of extensor MNs the extracted excitatory and inhibitory synaptic conductances alternate but with a predominance of inhibitory conductances, most pronounced in extensors. These conductance changes are consistent with a “push–pull” operation of locomotor CPG. The extracted excitatory and inhibitory synaptic conductances varied between 2 and 56% of the mean total conductance. Analysis of the phase tuning of the extracted synaptic conductances in flexor and extensor MNs in the rostral lumbar cord showed that the flexor-phase–related synaptic conductance changes have sharper locomotor-phase tuning than the extensor-phase–related conductances, suggesting a modular organization of premotor CPG networks consisting of reciprocally coupled, but differently composed, flexor and extensor CPG networks. There was a clear difference between phase tuning in rostral and caudal MNs, suggesting a distinct operation of CPG networks in different lumbar segments. The highly asymmetric features were preserved throughout all ranges of locomotor frequencies investigated and with different combinations of locomotor-inducing drugs. The asymmetric nature of CPG operation and phase tuning of the conductance profiles provide important clues to the organization of the rodent locomotor CPG and are compatible with a multilayered and distributed structure of the network.
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Anderson, Jeffrey S., Matteo Carandini, and David Ferster. "Orientation Tuning of Input Conductance, Excitation, and Inhibition in Cat Primary Visual Cortex." Journal of Neurophysiology 84, no. 2 (August 1, 2000): 909–26. http://dx.doi.org/10.1152/jn.2000.84.2.909.
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The input conductance of cells in the cat primary visual cortex (V1) has been shown recently to grow substantially during visual stimulation. Because increasing conductance can have a divisive effect on the synaptic input, theoretical proposals have ascribed to it specific functions. According to the veto model, conductance increases would serve to sharpen orientation tuning by increasing most at off-optimal orientations. According to the normalization model, conductance increases would control the cell's gain, by being independent of stimulus orientation and by growing with stimulus contrast. We set out to test these proposals and to determine the visual properties and possible synaptic origin of the conductance increases. We recorded the membrane potential of cat V1 cells while injecting steady currents and presenting drifting grating patterns of varying contrast and orientation. Input conductance grew with stimulus contrast by 20–300%, generally more in simple cells (40–300%) than in complex cells (20–120%), and in simple cells was strongly modulated in time. Conductance was invariably maximal for stimuli of the preferred orientation. Thus conductance changes contribute to a gain control mechanism, but the strength of this gain control does not depend uniquely on contrast. By assuming that the conductance changes are entirely synaptic, we further derived the excitatory and inhibitory synaptic conductances underlying the visual responses. In simple cells, these conductances were often arranged in push-pull: excitation increased when inhibition decreased and vice versa. Excitation and inhibition had similar preferred orientations and did not appear to differ in tuning width, suggesting that the intracortical synaptic inputs to simple cells of cat V1 originate from cells with similar orientation tuning. This finding is at odds with models where orientation tuning in simple cells is achieved by inhibition at off-optimal orientations or sharpened by inhibition that is more broadly tuned than excitation.
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Kolaj, Michal, and Richard Smith. "Using spatial derivatives of electromagnetic data to map lateral conductance variations in thin-sheet models: Applications over mine tailings ponds." GEOPHYSICS 78, no. 5 (September 1, 2013): E225—E235. http://dx.doi.org/10.1190/geo2012-0457.1.
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Mine waste, variable overburden, and the saprolite associated with nickel laterites have conductivity thicknesses (conductances) that vary laterally. In order for electromagnetic methods to be used to easily map lateral changes in conductance over thin-sheet-like bodies such as these, a simple conductance estimation method has been developed from Price’s equation. Through forward modeling, we found that assuming a uniform conductance and solving for an apparent conductance was sensitive enough to identify lateral conductance changes. The method was independent of the transmitter location, and each measurement provided a direct estimate of the apparent conductance below that station. The receiver can be moved around quickly allowing for lateral variations in apparent conductance to be determined efficiently. However, one of the required terms in the equation used is the vertical derivative of the secondary vertical magnetic field ([Formula: see text]). The accurate measurement of spatial electromagnetic derivatives requires a good signal-to-noise ratio (S/N), which can be hampered by low derivative signal values. Field studies performed over a dry tailings pond in Sudbury, Ontario, Canada, showed that an S/N greater than three was achievable even with [Formula: see text] values of less than [Formula: see text]. Apparent conductance estimates revealed that the tailings had a large resistive zone associated with surface vegetation, which may be correlated with favorable growing conditions and/or less conductive or thinner tailing material. Larger apparent conductances in other areas may be related to zones of thicker tailings and/or more conductive material (possibly due to increased metal content). Further drilling and sampling work is required to answer these ambiguities. Regardless, mapping the conductance of a thin sheet is an important step toward assessing if there are leftover metals in mine waste. However, the developed method is general and can be used in many other situations involving laterally varying thin bodies.
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Prinz, Astrid A., and Peter Fromherz. "Effect of Neuritic Cables on Conductance Estimates for Remote Electrical Synapses." Journal of Neurophysiology 89, no. 4 (April 1, 2003): 2215–24. http://dx.doi.org/10.1152/jn.00956.2002.
Full textAbstract:
The conductance of electrical synapses is usually estimated from voltage recordings at the neuronal somata under the assumption that each cell is isopotential. This approach neglects effects of intervening neurites. For a cell pair with unbranched neurites and an electrical synapse at their ends, we used cable theory to derive an analytical expression that relates the synaptic conductance to voltage recordings at the cell bodies and to the neurite properties. The equation implies that the conventional method significantly underestimates the actual synapse conductance if the neurite length is comparable to the electrotonic length constant and if the synaptic conductance is similar to the serial neurite conductance. For an experimental test, we cultured pairs of snail neurons on protein patterns, resulting in a geometry that matched the theoretical model. Using the isopotential theory, we estimated the synapse conductances and found them to be rather weak. To obtain the cable properties, we recorded spatiotemporal maps of signal propagation in the neurites using a voltage-sensitive dye. Fits of these maps to a passive cable model showed that the snail neurons are electrotonically rather compact. Given these features of our experimental system, the synaptic conductances derived with the nonisopotential model deviated from the estimates of the isopotential theory by about 13%. This discrepancy, although small, shows that even in electrotonically compact neurons coupled by weak synapses the impact of the neuritic cables on conductance estimates cannot be neglected. When applied to less compact and more strongly coupled cell pairs in vivo, our approach can supply the realistic estimates of synaptic conductances that are necessary for a better understanding of the role of electrical coupling in neural systems.
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Curran-Everett, D., K. G. Morris, and L. G. Moore. "Regional circulatory contributions to increased systemic vascular conductance of pregnancy." American Journal of Physiology-Heart and Circulatory Physiology 261, no. 6 (December 1, 1991): H1842—H1847. http://dx.doi.org/10.1152/ajpheart.1991.261.6.h1842.
Full textAbstract:
In pregnancy, maternal systemic vascular conductance increases, a new vascular circuit grows, and the maternal systemic circulation develops a diminished pressor response to angiotensin II (ANG II). However, the quantitative contributions of the latter two circulatory changes to the increased systemic vascular conductance of pregnancy have not been explored. In this experiment, we examined regional circulatory contributions to the increased systemic vascular conductance in conscious, late-gestation guinea pigs. Systemic arterial pressure, cardiac output (dye dilution), and regional blood flows (radiolabeled microspheres) were measured during baseline conditions and progressive ANG II infusion. Systemic and regional conductances were calculated from arterial pressure and cardiac output or regional blood flows. In pregnancy, maternal systemic vascular conductance increased from 3.2 to 5.0 ml.min-1.mmHg-1 (P less than 0.001); increased nonuteroplacental conductance contributed 71% to the increase in whole body conductance. Pregnancy tended to decrease the nonuteroplacental conductance response (P = 0.072), but did not change the uteroplacental conductance response (P greater than or equal to 0.29), to ANG II. The increased uteroplacental blood flow of pregnancy was preserved during ANG II-induced vasoconstriction. We conclude that maternal systemic vascular conductance increased primarily because nonuteroplacental vascular conductance increased.(ABSTRACT TRUNCATED AT 250 WORDS)
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Nakahari, T., and Y. Marunaka. "ADH-evoked [Cl-]i-dependent transient in whole cell current of distal nephron cell line A6." American Journal of Physiology-Renal Physiology 268, no. 1 (January 1, 1995): F64—F72. http://dx.doi.org/10.1152/ajprenal.1995.268.1.f64.
Full textAbstract:
The effect of antidiuretic hormone (ADH) on a distal nephron cell line (A6) was studied using the whole cell patch-clamp technique. A6 cells were cultured on a permeable support filter for 10-14 days in media containing 10% fetal bovine serum without supplemental aldosterone. In the unstimulated condition A6 cells had very small conductances of Na+,K+, and Cl-. Arginine vasotocin (AVT, 140 mU/ml, 280 nM) evoked a "transient" increase in whole cell currents as did dibutyryl-adenosine 3',5'-cyclic monophosphate (5 mM). These transients consisted of two components; one was the nonselective cation conductance, and the other was the Cl- conductance. Activation of these conductances was dependent on intracellular Cl- concentration ([Cl-]i). At low [Cl-]i (< or = 50 mM) both conductances were activated, whereas when [Cl-]i was 80 mM, only the Cl- conductance was activated. At high [Cl-]i (125 mM), both conductances were inhibited. It seems likely that the [Cl-]i maintained at a low level (< or = 50 mM) is an important requirement for A6 cells to respond to AVT.
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Moore, L. K., E. C. Beyer, and J. M. Burt. "Characterization of gap junction channels in A7r5 vascular smooth muscle cells." American Journal of Physiology-Cell Physiology 260, no. 5 (May 1, 1991): C975—C981. http://dx.doi.org/10.1152/ajpcell.1991.260.5.c975.
Full textAbstract:
Recent evidence suggest that coordination of blood flow in the microcirculation involves cell-to-cell coupling via gap junctions. In this study, using A7r5 cells as a model of vascular smooth muscle, we have characterized the gap junctions in terms of the unitary conductances of the observed channels, the responses to second messengers, and subunit protein composition. The cells were typically well coupled several hours after plating, with junctional conductances on the order 20-40 nS. Channels with mean conductances of 36 and 89 pS were observed in low-conductance cell pairs and in cell pairs whose macroscopic conductance was reduced by exposure to halothane. Connexin43 was the only known gap junction sequence detected by Northern blots (low and high stringency), immunoblots, or immunohistochemical studies. Junctional conductance was reduced 15% by 8-bromoadenosine 3',5'-cyclic monophosphate; 8-bromoguanosine 3',5'-cyclic monophosphate had no effect. The results suggest that connexin43 can form stable channels of at least two distinct conductances and gap junctions with differing responses to second messengers.
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Taylor, Adam L., Timothy J. Hickey, Astrid A. Prinz, and Eve Marder. "Structure and Visualization of High-Dimensional Conductance Spaces." Journal of Neurophysiology 96, no. 2 (August 2006): 891–905. http://dx.doi.org/10.1152/jn.00367.2006.
Full textAbstract:
Neurons, and realistic models of neurons, typically express several different types of voltage-gated conductances. These conductances are subject to continual regulation. Therefore it is essential to understand how changes in the conductances of a neuron affect its intrinsic properties, such as burst period or delay to firing after inhibition of a particular duration and magnitude. Even in model neurons, it can be difficult to visualize how the intrinsic properties vary as a function of their underlying maximal conductances. We used a technique, called clutter-based dimension reordering (CBDR), which enabled us to visualize intrinsic properties in high-dimensional conductance spaces. We applied CBDR to a family of models with eight different types of voltage- and calcium-dependent channels. CBDR yields images that reveal structure in the underlying conductance space. CBDR can also be used to visualize the results of other types of analysis. As examples, we use CBDR to visualize the results of a connected-components analysis, and to visually evaluate the results of a separating-hyperplane (i.e., linear classifier) analysis. We believe that CBDR will be a useful tool for visualizing the conductance spaces of neuronal models in many systems.
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Dubin, A. E., and V. E. Dionne. "Modulation of Cl-, K+, and nonselective cation conductances by taurine in olfactory receptor neurons of the mudpuppy Necturus maculosus." Journal of General Physiology 101, no. 4 (April 1, 1993): 469–85. http://dx.doi.org/10.1085/jgp.101.4.469.
Full textAbstract:
Odors are transduced by processes that modulate the membrane conductance of olfactory receptor neurons. Olfactory neurons from the aquatic salamander, Necturus maculosus, were acutely isolated without enzymes and studied with a resistive whole-cell method to minimize loss of soluble intracellular constituents. 55 of 224 neurons responded to the test compound taurine at concentrations between 10 nM and 100 microM. Four different conductance changes were elicited by taurine: an increased Cl- conductance (33%), an increased nonselective cation conductance (15%), a decreased Cl- conductance (15%), and a decreased K+ conductance (15%); in addition, responses too small to be characterized were elicited in some neurons. In most cases, taurine appeared to modulate only a single conductance in any particular cell. Modulation of each conductance was dose dependent, and each response ran down quickly in the normal whole-cell mode, presumably due to washout of a diffusible component in the transduction pathway. Modulation of taurine-sensitive conductances caused either inhibitory or excitatory responses. A similar diversity of responses in vivo would produce a complex pattern of electrical activity that could encode the identity and characteristics of an odor.
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Haldar, Purushottam, and Bijan Das. "Electrical Conductances of Tetrabutylammonium Bromide, Sodium Tetraphenylborate and Sodium Bromide in 2-Ethoxyethanol in the Temperature Range 35–50°C." Zeitschrift für Physikalische Chemie 218, no. 5 (May 1, 2004): 599–610. http://dx.doi.org/10.1524/zpch.218.5.599.30503.
Full textAbstract:
AbstractThe electrical conductances of the solutions of tetrabutylammonium bromide (Bu4NBr), sodium tetraphenylborate (NaPh4B) and sodium bromide (NaBr) in 2-ethoxyethanol have been reported at 35, 40, 45 and 50°C. The conductance data have been analyzed by the 1978 Fuoss conductance–concentration equation in terms of the limiting molar conductance (Λ0), the association constant (KΛ) and the association diameter (R). The ionic contributions to the limiting molar conductances (Λ0) have been estimated using the “reference electrolyte” tetrabutylammonium tetraphenylborate (Bu4NPh4B). Appreciable ionic association was observed for all of these electrolytes which were found to exist in the form of solvent-separated ion-pairs in 2-ethoxyethanol. The tetrabutylammonium and tetraphenylborate ions are found to remain scarcely solvated whereas the sodium and bromide ions undergo substantial solvation in 2-ethoxyethanol medium in the temperature range investigated here.
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Hawks, C., J. Elorza, A. Witt, D. Laroze, I. R. Cantalapiedra, A. Peñaranda, B. Echebarria, and J. Bragard. "Gap Junction Dynamics Induces Localized Conductance Bistability in Cardiac Tissue." International Journal of Bifurcation and Chaos 29, no. 08 (July 2019): 1930021. http://dx.doi.org/10.1142/s0218127419300210.
Full textAbstract:
Connexins are specialized ionic channels that control the action potential propagation between cardiac myocytes. In this paper, we study the connexin dynamics in a one-dimensional model of cardiac tissue. We show that the connexin dynamics may lead to a spatial organization of the gap junction conductance. In the numerical simulations presented in this paper we have found two different regimes for the spatial organization of the conductances: (a) a spatially uniform conductance; (b) a spatially complex pattern of local values of high and low conductances. In addition, we have observed that, locally, the two final states are limit cycles with a period equal to the period associated with the external excitation of the tissue strand. The conductance dispersion usually takes place on a very large time scale, i.e. thousands of heart beats, and on a very short spatial scale. Due to its simplicity, the one-dimensional setting allows a detailed study of the emerging structure and in particular very long simulations. We have studied the transition between the two aforementioned states as a function of the gap junction conductance characteristics. Furthermore, we have studied the effect of initially added noises on the outcome of the system. Finally, using spatial autocorrelation functions we have characterized the spatial dispersion in conductance values.
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Papadopoulos, N. "The conductance behaviour of NaBPh4 in acetonitrile–toluene mixtures at 15,25, and 35 °C." Canadian Journal of Chemistry 67, no. 10 (October 1, 1989): 1624–27. http://dx.doi.org/10.1139/v89-248.
Full textAbstract:
The limiting molar conductances and association constants for NaBPh4 have been evaluated in acentonitrile–toluene mixtures at 15, 25, and 35 °C. Experimental data have been analysed by the Lee–Wheaton conductance equation. The thermodynamic parameters of the non-coulombic interaction have been evaluated. Keywords: conductance, association constant, Lee–Wheaton equation, acetonitrile–toulene.
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Lindau, M., and J. M. Fernandez. "A patch-clamp study of histamine-secreting cells." Journal of General Physiology 88, no. 3 (September 1, 1986): 349–68. http://dx.doi.org/10.1085/jgp.88.3.349.
Full textAbstract:
The ionic conductances in rat basophilic leukemia cells (RBL-2H3) and rat peritoneal mast cells were investigated using the patch-clamp technique. These two cell types were found to have different electrophysiological properties in the resting state. The only significant conductance of RBL-2H3 cells was a K+-selective inward rectifier. The single channel conductance at room temperature increased from 2-3 pS at 2.8 mM external K+ to 26 pS at 130 mM K+. This conductance, which appeared to determine the resting potential, could be blocked by Na+ and Ba2+ in a voltage-dependent manner. Rat peritoneal mast cells had a whole-cell conductance of only 10-30 pS, and the resting potential was close to zero. Sometimes discrete openings of channels were observed in the whole-cell configuration. When the Ca2+ concentration on the cytoplasmic side of the membrane was elevated, two types of channels with poor ion specificity appeared. A cation channel, observed at a Ca2+ concentration of approximately 1 microM, had a unit conductance of 30 pS. The other channel, activated at several hundred micromolar Ca2+, was anion selective and had a unit conductance of approximately 380 pS in normal Ringer solution and a bell-shaped voltage dependence. Antigenic stimulation did not cause significant changes in the ionic conductances in either cell type, which suggests that these cells use a mechanism different from ionic currents in stimulus-secretion coupling.
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Sellin, J. H., A. Hall, E. J. Cragoe, and W. P. Dubinsky. "Characterization of an apical sodium conductance in rabbit cecum." American Journal of Physiology-Gastrointestinal and Liver Physiology 264, no. 1 (January 1, 1993): G13—G21. http://dx.doi.org/10.1152/ajpgi.1993.264.1.g13.
Full textAbstract:
Rabbit cecum in vitro exhibits electrogenic Na+ absorption not blocked by amiloride but inhibited by the amiloride analogue phenamil, suggesting transport mediated by modified Na+ channels in the apical membrane. To further characterize the mechanism(s) of Na+ absorption, microelectrode impalements of single epithelial cells were performed to measure intracellular potential difference (psi mc) and fractional resistance of the apical membrane, to characterize ionic conductances of the apical and basolateral membranes, and to determine the response to phenamil. The electrical potential profile of cecum (psi mc = -31 +/- 2 mV, fractional resistance = 0.71 +/- 0.03) was qualitatively similar to distal colon. The apical membrane exhibited responses suggesting both Na+ and K+ conductances, whereas the basolateral membrane appeared to have a predominant K+ conductance. Phenamil elicited a depolarization of psi mc and a decrease in fractional resistance; neither response is consistent with inhibition of an apical Na+ conductance. Studies were performed in apical membrane vesicles to characterize ionic conductances by a second independent methodology. These additional studies confirmed the presence of an apical Na+ conductance not inhibited by either amiloride or phenamil. Thus both microelectrode impalement and vesicle studies demonstrated an apical membrane Na+ conductance in rabbit cecum; this is the likely mechanism of electrogenic Na+ absorption in this epithelium. However, the anomalous response to phenamil suggests that the inhibitory effect of this agent is not directly on the conductance. The cecal transporter may be one of a family of cation channels related to, but significantly different from, the classic Na+ channel found in distal colon and other tight epithelia.
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Rathour, Rahul Kumar, and Rishikesh Narayanan. "Influence fields: a quantitative framework for representation and analysis of active dendrites." Journal of Neurophysiology 107, no. 9 (May 1, 2012): 2313–34. http://dx.doi.org/10.1152/jn.00846.2011.
Full textAbstract:
Neuronal dendrites express numerous voltage-gated ion channels (VGICs), typically with spatial gradients in their densities and properties. Dendritic VGICs, their gradients, and their plasticity endow neurons with information processing capabilities that are higher than those of neurons with passive dendrites. Despite this, frameworks that incorporate dendritic VGICs and their plasticity into neurophysiological and learning theory models have been far and few. Here, we develop a generalized quantitative framework to analyze the extent of influence of a spatially localized VGIC conductance on different physiological properties along the entire stretch of a neuron. Employing this framework, we show that the extent of influence of a VGIC conductance is largely independent of the conductance magnitude but is heavily dependent on the specific physiological property and background conductances. Morphologically, our analyses demonstrate that the influences of different VGIC conductances located on an oblique dendrite are confined within that oblique dendrite, thus providing further credence to the postulate that dendritic branches act as independent computational units. Furthermore, distinguishing between active and passive propagation of signals within a neuron, we demonstrate that the influence of a VGIC conductance is spatially confined only when propagation is active. Finally, we reconstruct functional gradients from VGIC conductance gradients using influence fields and demonstrate that the cumulative contribution of VGIC conductances in adjacent compartments plays a critical role in determining physiological properties at a given location. We suggest that our framework provides a quantitative basis for unraveling the roles of dendritic VGICs and their plasticity in neural coding, learning, and homeostasis.
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Verheijck, E. Etienne, Ronald Wilders, Ronald W. Joyner, David A. Golod, Rajiv Kumar, Habo J. Jongsma, Lennart N. Bouman, and Antoni C. G. van Ginneken. "Pacemaker Synchronization of Electrically Coupled Rabbit Sinoatrial Node Cells." Journal of General Physiology 111, no. 1 (January 1, 1998): 95–112. http://dx.doi.org/10.1085/jgp.111.1.95.
Full textAbstract:
The effects of intercellular coupling conductance on the activity of two electrically coupled isolated rabbit sinoatrial nodal cells were investigated. A computer-controlled version of the “coupling clamp” technique was used in which isolated sinoatrial nodal cells, not physically in contact with each other, were electrically coupled at various values of ohmic coupling conductance, mimicking the effects of mutual interaction by electrical coupling through gap junctional channels. We demonstrate the existence of four types of electrical behavior of coupled spontaneously active cells. As the coupling conductance is progressively increased, the cells exhibit: (a) independent pacemaking at low coupling conductances, (b) complex dynamics of activity with mutual interactions, (c) entrainment of action potential frequency at a 1:1 ratio with different action potential waveforms, and (d) entrainment of action potentials at the same frequency of activation and virtually identical action potential waveforms. The critical value of coupling conductance required for 1:1 frequency entrainment was <0.5 nS in each of the five cell pairs studied. The common interbeat interval at a relatively high coupling conductance (10 nS), which is sufficient to produce entrainment of frequency and also identical action potential waveforms, is determined most by the intrinsically faster pacemaker cell and it can be predicted from the diastolic depolarization times of both cells. Evidence is provided that, at low coupling conductances, mutual pacemaker synchronization results mainly from the phase-resetting effects of the action potential of one cell on the depolarization phase of the other. At high coupling conductances, the tonic, diastolic interactions become more important.
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Sivaramakrishnan, S., G. D. Bittner, and M. S. Brodwick. "Calcium-activated potassium conductance in presynaptic terminals at the crayfish neuromuscular junction." Journal of General Physiology 98, no. 6 (December 1, 1991): 1161–79. http://dx.doi.org/10.1085/jgp.98.6.1161.
Full textAbstract:
Membrane potential changes that typically evoke transmitter release were studied by recording intracellularly from the excitor axon near presynaptic terminals of the crayfish opener neuromuscular junction. Depolarization of the presynaptic terminal with intracellular current pulses activated a conductance that caused a decrease in depolarization during the constant current pulse. This conductance was identified as a calcium-activated potassium conductance, gK(Ca), by its disappearance in a zero-calcium/EGTA medium and its block by cadmium, barium, tetraethylammonium ions, and charybdotoxin. In addition to gK(Ca), a delayed rectifier potassium conductance (gK) is present in or near the presynaptic terminal. Both these potassium conductances are involved in the repolarization of the membrane during a presynaptic action potential.
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Halm, D. R., E. J. Krasny, and R. A. Frizzell. "Electrophysiology of flounder intestinal mucosa. I. Conductance properties of the cellular and paracellular pathways." Journal of General Physiology 85, no. 6 (June 1, 1985): 843–64. http://dx.doi.org/10.1085/jgp.85.6.843.
Full textAbstract:
We evaluated the conductances for ion flow across the cellular and paracellular pathways of flounder intestine using microelectrode techniques and ion-replacement studies. Apical membrane conductance properties are dominated by the presence of Ba-sensitive K channels. An elevated mucosal solution K concentration, [K]m, depolarized the apical membrane potential (psi a) and, at [K]m less than 40 mM, the K dependence of psi a was abolished by 1-2 mM mucosal Ba. The basolateral membrane displayed Cl conductance behavior, as evidenced by depolarization of the basolateral membrane potential (psi b) with reduced serosal Cl concentrations, [Cl]s. psi b was unaffected by changes in [K]s or [Na]s. From the effect of mucosal Ba on transepithelial K selectivity, we estimated that paracellular conductance (Gp) normally accounts for 96% of transepithelial conductance (Gt). The high Gp attenuates the contribution of the cellular pathway to psi t while permitting the apical K and basolateral Cl conductances to influence the electrical potential differences across both membranes. Thus, psi a and psi b (approximately 60 mV, inside negative) lie between the equilibrium potentials for K (76 mV) and Cl (40 mV), thereby establishing driving forces for K secretion across the apical membrane and Cl absorption across the basolateral membrane. Equivalent circuit analysis suggests that apical conductance (Ga approximately equal to 5 mS/cm2) is sufficient to account for the observed rate of K secretion, but that basolateral conductance (Gb approximately equal to 1.5 mS/cm2) would account for only 50% of net Cl absorption. This, together with our failure to detect a basolateral K conductance, suggests that Cl absorption across this barrier involves KCl co-transport.
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Krieger, C., and T. A. Sears. "The development of voltege-dependent ionic conductances In murine spinal cord neurones in culture." Canadian Journal of Physiology and Pharmacology 66, no. 10 (October 1, 1988): 1328–36. http://dx.doi.org/10.1139/y88-217.
Full textAbstract:
The development of voltage-dependent ionic conductances of foetal mouse spinal cord neurones was examined using the whole-cell patch-clamp technique on neurones cultured from embryos aged 10–12 days (E10–E12) which were studied between the first day in vitro (V1) to V10. A delayed rectifier potassium conductance (IK) and a leak conductance were observed in neurones of E10.V1, E11, V1, and E12, V1 as well as in neurones cultured for longer periods. A rapidly activating and inactivating potassium conductance (IA) was seen in neurones from E11, V2 and E12, V1 and at longer times in vitro. A tetrodotoxin (TTX) sensitive sodium-dependent inward current was observed in neurones of E11 and E12 from V1 onwards. Calcium-dependent conductances were not detectable in these neurones unless the external calcium concentration was raised 10- to 20-foid and potassium conductances were blocked. Under these conditions calcium currents could be observed as early as E11, V3 and E12, V2 and at subsequent times in vitro. The pattern of development of voltage-dependent ionic conductances in murine spinal neurones is such that initially leak and potassium currents are present followed by sodium current and subsequently calcium current.
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Cao, Xiao-Jie, and Donata Oertel. "Temperature Affects Voltage-Sensitive Conductances Differentially in Octopus Cells of the Mammalian Cochlear Nucleus." Journal of Neurophysiology 94, no. 1 (July 2005): 821–32. http://dx.doi.org/10.1152/jn.01049.2004.
Full textAbstract:
Temperature is an important physiological variable the influence of which on macroscopic electrophysiological measurements in slices is not well documented. We show that each of three voltage-sensitive conductances of octopus cells of the mammalian ventral cochlear nucleus (VCN) is affected differently by changes in temperature. As expected, the kinetics of the currents were faster at higher than at lower temperature. Where they could be measured, time constants of activation, deactivation, and inactivation had Q10 values between 1.8 and 4.6. The magnitude of the peak conductances was differentially affected by temperature. While the peak magnitude of the high-voltage-activated K+ conductance, gKH, was unaffected by changes in temperature, the peak of the low-voltage-activated K+ conductance, gKL, was reduced by half when the temperature was lowered from 33 to 23°C ( Q10 = 2). Changing the temperature changed the kinetics and the magnitude of the hyperpolarization-activated mixed cation conductance, gh, but the changes in magnitude were transient. The voltage sensitivity of the three conductances was unaffected by temperature. The action of temperature on these conductances is reflected in the resting potentials and in the shapes of action potentials.
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Cheng, C. Y., and C. K. Chen. "Efficiency Optimizations of an Irreversible Brayton Heat Engine." Journal of Energy Resources Technology 120, no. 2 (June 1, 1998): 143–48. http://dx.doi.org/10.1115/1.2795025.
Full textAbstract:
A steady-flow approach for finite-time thermodynamics is used to calculate the maximum thermal efficiency, its corresponding power output, adiabatic temperature ratio, and thermal-conductance ratio of heat transfer equipment of a closed Brayton heat engine. The physical model considers three types of irreversibilities: finite thermal conductance between the working fluid and the reservoirs, heat leaks between the reservoirs, and internal irreversibility inside the closed Brayton heat engine. The effects of heat leaks, hot-cold reservoir temperature ratios, turbine and compressor isentropic efficiencies, and total conductances of heat exchangers on the maximum thermal efficiency and its corresponding parameters are studied. The optimum conductance ratio could be found to effectively use the heat transfer equipment, and this ratio is increased as the component efficiencies and total conductances of heat exchangers are increased, and always less than or equal to 0.5.
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Ismael, Ali K., and Colin J. Lambert. "Single-molecule conductance oscillations in alkane rings." Journal of Materials Chemistry C 7, no. 22 (2019): 6578–81. http://dx.doi.org/10.1039/c8tc05565c.
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Chappell, Sarah, Carly Brooke, Richard J. Nichols, Laurence J. Kershaw Cook, Malcolm Halcrow, Jens Ulstrup, and Simon J. Higgins. "Evidence for a hopping mechanism in metal|single molecule|metal junctions involving conjugated metal–terpyridyl complexes; potential-dependent conductances of complexes [M(pyterpy)2]2+ (M = Co and Fe; pyterpy = 4′-(pyridin-4-yl)-2,2′:6′,2′′-terpyridine) in ionic liquid." Faraday Discussions 193 (2016): 113–31. http://dx.doi.org/10.1039/c6fd00080k.
Full textAbstract:
Extensive studies of various families of conjugated molecules in metal|molecule|metal junctions suggest that the mechanism of conductance is usually tunnelling for molecular lengths < ca. 4 nm, and that for longer molecules, coherence is lost as a hopping element becomes more significant. In this work we present evidence that, for a family of conjugated, redox-active metal complexes, hopping may be a significant factor for even the shortest molecule studied (ca. 1 nm between contact atoms). The length dependence of conductance for two series of such complexes which differ essentially in the number of conjugated 1,4-C6H4- rings in the structures has been studied, and it is found that the junction conductances vary linearly with molecular length, consistent with a hopping mechanism, whereas there is significant deviation from linearity in plots of log(conductance) vs. length that would be characteristic of tunnelling, and the slopes of the log(conductance)–length plots are much smaller than expected for an oligophenyl system. Moreover, the conductances of molecular junctions involving the redox–active molecules, [M(pyterpy)2]2+/3+ (M = Co, Fe) have been studied as a function of electrochemical potential in ionic liquid electrolyte, and the conductance–overpotential relationship is found to fit well with the Kuznetsov–Ulstrup relationship, which is essentially a hopping description.
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Bal, Ramazan, and Donata Oertel. "Potassium Currents in Octopus Cells of the Mammalian Cochlear Nucleus." Journal of Neurophysiology 86, no. 5 (November 1, 2001): 2299–311. http://dx.doi.org/10.1152/jn.2001.86.5.2299.
Full textAbstract:
Octopus cells in the posteroventral cochlear nucleus (PVCN) of mammals are biophysically specialized to detect coincident firing in the population of auditory nerve fibers that provide their synaptic input and to convey its occurrence with temporal precision. The precision in the timing of action potentials depends on the low input resistance (∼6 MΩ) of octopus cells at the resting potential that makes voltage changes rapid (τ ∼ 200 μs). It is the activation of voltage-dependent conductances that endows octopus cells with low input resistances and prevents repetitive firing in response to depolarization. These conductances have been examined under whole cell voltage clamp. The present study reveals the properties of two conductances that mediate currents whose reversal at or near the equilibrium potential for K+ over a wide range of extracellular K+ concentrations identifies them as K+ currents. One rapidly inactivating conductance, g KL, had a threshold of activation at −70 mV, rose steeply as a function of depolarization with half-maximal activation at −45 ± 6 mV (mean ± SD), and was fully activated at 0 mV. The low-threshold K+ current ( I KL) was largely blocked by α-dendrotoxin (α-DTX) and partially blocked by DTX-K and tityustoxin, indicating that this current was mediated through potassium channels of the Kv1 (also known as shakeror KCNA) family. The maximum low-threshold K+conductance ( g KL) was large, 514 ± 135 nS. Blocking I KL with α-DTX revealed a second K+ current with a higher threshold ( I KH) that was largely blocked by 20 mM tetraethylammonium (TEA). The more slowly inactivating conductance, g KH, had a threshold for activation at −40 mV, reached half-maximal activation at −16 ± 5 mV, and was fully activated at +30 mV. The maximum high-threshold conductance, g KH, was on average 116 ± 27 nS. The present experiments show that it is not the biophysical and pharmacological properties but the magnitude of the K+ conductances that make octopus cells unusual. At the resting potential, −62 mV, g KLcontributes ∼42 nS to the resting conductance and mediates a resting K+ current of 1 nA. The resting outward K+ current is balanced by an inward current through the hyperpolarization-activated conductance, g h, that has been described previously.
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Moore, L. K., and J. M. Burt. "Gap junction function in vascular smooth muscle: influence of serotonin." American Journal of Physiology-Heart and Circulatory Physiology 269, no. 4 (October 1, 1995): H1481—H1489. http://dx.doi.org/10.1152/ajpheart.1995.269.4.h1481.
Full textAbstract:
In this study we examined the effects of serotonin (5-hydroxytryptamine, 5-HT) on the function of gap junctions between smooth muscle cells isolated from human and pig coronary and rat mesentery arteries and between A7r5 cells (cell line derived from embryonic rat aorta). Mesentery and pig coronary cells expressed connexin (Cx) 43, and human coronary cells expressed Cx40. Mesentery and pig coronary cells each exhibited a single gap junction channel population with unitary conductances of 75 and 59 pS, respectively. Human coronary cells exhibited two channel populations with unitary conductances of 51 and 107 pS. The A7r5 cells express Cx40 and Cx43 and exhibit three channel populations with unitary conductances of 70, 108, and 141 pS. Under control conditions, junctional conductance between the four cell types ranged from 11 to 20 nS. During maximal stimulation with 5-HT (1-10 microM), junctional conductance increased (29-75%) in all four cell types. The unitary conductance profiles in the rat mesentery and pig coronary cells were unaffected by 5-HT, suggesting that the observed increase in macroscopic conductance reflects an increase in open probability. Unitary conductances were also unaffected in the human coronary and A7r5 cells. However, there was a reduced frequency of the 105-pS channel in the human coronary cells and of the 70- and 141-pS channels in the A7r5 cells. These changes in the relative frequency histograms suggest that the open probabilities of the various channel types are differentially affected by the 5-HT treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
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Gray, Daniel A., Gustavo Frindt, and Lawrence G. Palmer. "Quantification of K+ secretion through apical low-conductance K channels in the CCD." American Journal of Physiology-Renal Physiology 289, no. 1 (July 2005): F117—F126. http://dx.doi.org/10.1152/ajprenal.00471.2004.
Full textAbstract:
Outward and inward currents through single small-conductance K+ (SK) channels were measured in cell-attached patches of the apical membrane of principal cells of the rat cortical collecting duct (CCD). Currents showed mild inward rectification with high [K+] in the pipette (Kp+), which decreased as Kp+ was lowered. Inward conductances had a hyperbolic dependence on Kp+ with half-maximal conductance at ∼20 mM. Outward conductances, measured near the reversal potential, also increased with Kp+ from 15 pS (Kp+ = 0) to 50 pS (Kp+ = 134 mM). SK channel density was measured as the number of conducting channels per patch in cell-attached patches. As reported previously, channel density increased when animals were on a high-K diet for 7 days. Addition of 8-cpt-cAMP to the bath at least 5 min before making a seal increased SK channel density to an even greater extent, although this increase was not additive with the effect of a high-K diet. In contrast, increases in Na channel activity, assessed as the whole cell amiloride-sensitive current, due to K loading and 8-cpt-cAMP treatment were additive. Single-channel conductances and channel densities were used as inputs to a simple mathematical model of the CCD to predict rates of transepithelial Na+ and K+ transport as a function of apical Na+ permeability and K+ conductance, basolateral pump rates and K+ conductance, and the paracellular conductance. With measured values for these parameters, the model predicted transport rates that were in good agreement with values measured in isolated, perfused tubules. The number and properties of SK channels account for K+ transport by the CCD under all physiological conditions tested.
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Kaka, Kosrat N., Anis A. Al-Najar, and Wali M. Hamad. "The Audio Frequency Conductance Study of Some Metal Succinate Salts in Aqueous Medium at Different Temperatures (Part I: Magnesium, Manganese (II), Barium and Copper Succinates)." Journal of Chemistry 2013 (2013): 1–10. http://dx.doi.org/10.1155/2013/858374.
Full textAbstract:
The audio electrical conductances of aqueous solutions of magnesium, manganese II, barium, and copper succinates have been measured at various temperatures in the range of 298.15 K to 313.15 K, using an audio frequency conductance bridge. The evaluation of conductance data was carried out by minimisation technique using the theoretical equations of the complete and modified forms of Pitts (P) and Fuoss-Hsia (F-H), each a three-parameter equation, association constant (KA), molar conductance (Λm), and distance parameter (a). Quantitative results showed that these salts do not behave as “strong” electrolytes, and that their dissociations are far from complete. The abnormally low conductances of these electrolytes are not due to the presence of electrically neutral molecules but to the ion-pair formation. The Walden product values, as well as the standard thermodynamics functions (ΔH∘,ΔG∘,ΔS∘) for the association reaction at the four temperatures studied, have been evaluated.
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Antar, Mohamed A., and Syed M. Zubair. "Thermoeconomic Considerations in the Optimum Allocation of Heat Transfer Inventory for Refrigeration and Heat Pump Systems." Journal of Energy Resources Technology 124, no. 1 (March 1, 2002): 28–33. http://dx.doi.org/10.1115/1.1446070.
Full textAbstract:
Thermoeconomics is defined as attaching monetary values to heat exchanger conductances of a given plant. In this study, optimum allocation of heat transfer inventory for heat exchangers in a refrigeration system with specified power input or cooling capacity, and for a heat pump with specified heating capacity is investigated. The ratio of hot- to cold-end conductance unit cost ratio, G, was considered in the analysis as an additional parameter of considerable importance to the designer. A closed-form expression is given in terms of unit cost of conductances of both the heat exchangers. The results show a strong dependence of the total cost on the absolute temperature ratios as well as the hot- to the cold-end conductance cost ratio. It is demonstrated in the illustrative example that for G=0.1, the conductance of the hot-end heat exchanger is about three times the cold-end heat exchanger.
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Meng, X. J., and S. A. Weinman. "cAMP- and swelling-activated chloride conductance in rat hepatocytes." American Journal of Physiology-Cell Physiology 271, no. 1 (July 1, 1996): C112—C120. http://dx.doi.org/10.1152/ajpcell.1996.271.1.c112.
Full textAbstract:
An outwardly rectifying Cl- conductance was identified in primary isolated rat hepatocytes, and the whole cell patch-clamp technique was used to characterize its properties and mechanisms of activation. With symmetrical Cl(-)-containing solutions on both sides and adenosine 3',5'-cyclic monophosphate (cAMP; 100 microM) in the pipette solution, a large outwardly rectifying conductance (1,014 +/- 153 pS/pF, n = 20) developed in all cells within 3 min. This cAMP-activated conductance was highly anion selective and slowly inactivated at voltages > 80 mV. It was completely inhibited by the anion channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid (200 microM, n = 6) and partially inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (150 microM, n = 7). It displayed a halide selectivity of I- > Br- > Cl-. In the absence of cAMP, a functionally similar conductance was activated by cell swelling. Reduction of bath osmolality from 300 to 250 mosmol/kg increased membrane conductance from 64 +/- 16.4 to 487 +/- 23 pS/pF (n = 4). This swelling-activated conductance was also highly anion selective and had identical halide selectivity and blocker sensitivity as the cAMP-activated conductance. Although cell swelling was not necessary for cAMP activation, cell shrinkage with hyperosmotic bath (350 mosmol/kg), either before or after exposure to cAMP, inhibited the cAMP-activated conductance. By the determination of conductance as a function of bath osmolality in the presence and absence of cAMP, it was observed that cAMP shifted the osmotic set point for conductance activation without changing either the maximum or minimum conductance. In conclusion, both cAMP and cell swelling activate a large outwardly rectifying Cl- conductance in rat hepatocytes. Its ionic selectivity and sensitivity to channel blockers are identical to those seen for swelling-activated Cl- conductances in many cell types. The conductive properties are not those of cystic fibrosis transmembrane conductance regulator-mediated Cl- conductance. cAMP appears to activate this conductance by altering the volume set point of a swelling-activated channel.
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Moorhouse, Andrew J., Angelo Keramidas, Andrey Zaykin, Peter R. Schofield, and Peter H. Barry. "Single Channel Analysis of Conductance and Rectification in Cation-selective, Mutant Glycine Receptor Channels." Journal of General Physiology 119, no. 5 (April 15, 2002): 411–25. http://dx.doi.org/10.1085/jgp.20028553.
Full textAbstract:
Members of the ligand-gated ion channel superfamily mediate fast synaptic transmission in the nervous system. In this study, we investigate the molecular determinants and mechanisms of ion permeation and ion charge selectivity in this family of channels by characterizing the single channel conductance and rectification of α1 homomeric human glycine receptor channels (GlyRs) containing pore mutations that impart cation selectivity. The A-1'E mutant GlyR and the selectivity double mutant ([SDM], A-1'E, P-2'Δ) GlyR, had mean inward chord conductances (at −60 mV) of 7 pS and mean outward conductances of 11 and 12 pS (60 mV), respectively. This indicates that the mutations have not simply reduced anion permeability, but have replaced the previous anion conductance with a cation one. An additional mutation to neutralize the ring of positive charge at the extracellular mouth of the channel (SDM+R19'A GlyR) made the conductance–voltage relationship linear (14 pS at both 60 and −60 mV). When this external charged ring was made negative (SDM+R19'E GlyR), the inward conductance was further increased (to 22 pS) and now became sensitive to external divalent cations (being 32 pS in their absence). The effects of the mutations to the external ring of charge on conductance and rectification could be fit to a model where only the main external energy barrier height for permeation was changed. Mean outward conductances in the SDM+R19'A and SDM+R19'E GlyRs were increased when internal divalent cations were absent, consistent with the intracellular end of the pore being flanked by fixed negative charges. This supports our hypothesis that the ion charge selectivity mutations have inverted the electrostatic profile of the pore by introducing a negatively charged ring at the putative selectivity filter. These results also further confirm the role of external pore vestibule electrostatics in determining the conductance and rectification properties of the ligand-gated ion channels.
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Sceniak, Michael P., and Shasta L. Sabo. "Modulation of Firing Rate by Background Synaptic Noise Statistics in Rat Visual Cortical Neurons." Journal of Neurophysiology 104, no. 5 (November 2010): 2792–805. http://dx.doi.org/10.1152/jn.00023.2010.
Full textAbstract:
It has been shown previously that background synaptic noise modulates the response gain of neocortical neurons. However, the role of the statistical properties of the noise in modulating firing rate is not known. Here, the dependence of firing rate on the statistical properties of the excitatory to inhibitory balance (EI) in cortical pyramidal neurons was studied. Excitatory glutamatergic and inhibitory GABAergic synaptic conductances were simulated as two stochastic processes and injected into individual neurons in vitro through use of the dynamic-clamp system. Response gain was significantly modulated as a function of the statistical interactions between excitatory and inhibitory synaptic conductances. Firing rates were compared for noisy synaptic conductance steps by varying either the EI correlation or the relative delay between correlated E and I. When inhibitory synaptic conductances exhibited a short temporal delay (5 ms) relative to correlated excitatory synaptic conductances, the response gain was increased compared with noise with no temporal delay but with an equivalent degree of correlation. The dependence of neuronal firing rate on the EI delay of the noisy background synaptic conductance suggests that individual excitatory pyramidal neurons are sensitive to the EI balance of the synaptic conductance. Therefore the statistical EI interactions encoded within the synaptic subthreshold membrane fluctuations are able to modulate neuronal firing properties.
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Tarran, R., M. A. Gray, M. J. Evans, W. H. Colledge, R. Ratcliff, and B. E. Argent. "Basal chloride currents in murine airway epithelial cells: modulation by CFTR." American Journal of Physiology-Cell Physiology 274, no. 4 (April 1, 1998): C904—C913. http://dx.doi.org/10.1152/ajpcell.1998.274.4.c904.
Full textAbstract:
We have isolated ciliated respiratory cells from the nasal epithelium of wild-type and cystic fibrosis (CF) null mice and used the patch-clamp technique to investigate their basal conductances. Current-clamp experiments on unstimulated cells indicated the presence of K+ and Cl− conductances and, under certain conditions, a small Na+conductance. Voltage-clamp experiments revealed three distinct Cl− conductances. I tv-indep was time and voltage independent with a linear current-voltage ( I- V) plot; I v-actexhibited activation at potentials greater than ±50 mV, giving an S-shaped I- Vplot; and I hyp-act was activated by hyperpolarizing potentials and had an inwardly rectified I- Vplot. The current density sequence was I hyp-act = I v-act ≫ I tv-indep. These conductances had Cl−-to- N-methyl-d-glucamine cation permeability ratios of between 2.8 and 10.3 and were unaffected by tamoxifen, flufenamate, glibenclamide, DIDS, and 5-nitro-2-(3-phenylpropylamino) benzoic acid but were inhibited by Zn2+ and Gd3+. I tv-indep and I v-act were present in wild-type and CF cells at equal density and frequency. However, I hyp-actwas detected in only 3% of CF cells compared with 26% of wild-type cells, suggesting that this conductance may be modulated by cystic fibrosis transmembrane conductance regulator (CFTR).