Voltage dependence of chloride current through Xenopus muscle membrane in alkaline solutions

1980 ◽  
Vol 58 (9) ◽  
pp. 999-1010 ◽  
Author(s):  
Peter C. Vaughan ◽  
James G. McLarnon ◽  
Donald D. F. Loo
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Chloride Conductance ◽  
Resting Potential ◽  
Muscle Membrane ◽  
Alkaline Solutions ◽  
Constant Field ◽  
Confined Space ◽  
Initial Current ◽  
Test Current

Three-microelectrode voltage-clamp experiments have been conducted on surface fibres of Xenopus laevis sartorius muscles. When potassium and chloride were substituted by rubidium and sulphate, negligibly small currents were observed. In solutions containing rubidium and chloride at pH 8.4–8.8 normally polarized fibres exhibited instantaneous current–voltage relations that were linear over a wide voltage range. Chloride conductance varied widely from fibre to fibre; the mean resting conductance at −80 mV was 7.4 × 10−4 ± 2.6 × 10−4 S/cm2 (mean ± SE). When hyperpolarizing voltage steps were made, conductance declined from the initial to the steady state; inward currents saturated near 14 μA/cm2. In experiments performed on fibres depolarized by immersion in K+-and Rb+-rich solutions it was found that resting conductance did not increase by as much as would be expected from constant field – constant permeability precepts, by comparison with normally polarized fibres. Despite the low chloride transmembrane concentration ratio, rectification in the steady state was similar in depolarized and normally polarized fibres.When a two-pulse protocol was employed to test the availability of chloride conductance after conditioning of the system at some voltage, it was found that the test current, the initial current at the onset of the test voltage step, depended sigmoidally on the conditioning voltage. The sigmoid relationships had asymptotic limits: after hyperpolarizing conditioning the test current was minimal, after depolarizing conditioning, maximal. Normalized sigmoid relations were superimposable, whether from normally polarized or chronically depolarized cells.When the protocol was repeated using different test potentials and initial currents following a particular conditioning voltage were plotted against the test potential, families of straight lines were obtained. The slopes of the members of these families were dependent on the conditioning voltage: the more negative the conditioning step the lower the slope. The lines projected through a mutual intersection at a voltage slightly more positive than the resting potential. This is interpreted as indicating that there is some voltage, slightly positive with respect to the membrane potential, at which the initial current is independent of the conditioning voltage.It is concluded that the state of the chloride conductance mechanism is a function of the deviation of the membrane from the resting potential rather than of the absolute membrane potential and that relaxations from initial to steady states reflect properties of the permeation mechanism rather than accumulation or depletion of chloride in a confined space, although some contribution by a mechanism such as the latter cannot be completely ruled out.

Some observations on the behaviour of chloride current–voltage relations in Xenopus muscle membrane in acid solutions

1981 ◽  
Vol 59 (1) ◽  
pp. 7-13 ◽  
Author(s):  
Donald D. F. Loo ◽  
James G. McLarnon ◽  
Peter C. Vaughan
Keyword(s):  
Steady State ◽  
Standard Test ◽  
Chloride Current ◽  
Chloride Conductance ◽  
Resting Potential ◽  
Single Type ◽  
Muscle Membrane ◽  
Wave Form ◽  
Solution Ph ◽  
Current Voltage

Chloride current–voltage relations in Xenopus laevis muscle membrane have been investigated in phosphate-buffered solution (pH 5.2–5.4) using a three-microelectrode voltage clamp. Resting chloride conductance in these conditions is about 10−4 S/cm2, approximately [Formula: see text]th that at pH 8.8. When the membrane potential is stepped from the holding (resting) potential to a more negative voltage the current rises from the initial to the steady state. The instantaneous current–voltage relation is linear and the steady-state relation shows inward-going rectification. As hyperpolarization appears to "activate" the chloride conductance, the "availability" of chloride current has been measured at the beginning of a voltage step to a standard test potential following conditioning at a variety of potentials. The relationship between the test current and the conditioning voltage is sigmoid. The normalized sigmoid curve has the same slope (absolute value) but opposite sign to that obtained in the same experiment at pH 8.8. In mildly acidic solutions (pH 6.4) the current wave form is diphasic: current initially falls then rises to the steady state. This combination of transients militates against the idea that transients are due solely to accumulation–depletion effects in restricted spaces ("unstirred layers") and a hypothesis is qualitatively outlined in which pH- and voltage-dependent effects are ascribed to a single type of channel whose orientation in the membrane is unconstrained.

scholarly journals Relative Ion Permeabilities in the Crayfish Giant Axon Determined from Rapid External Ion Changes

1967 ◽  
Vol 50 (7) ◽  
pp. 1929-1953 ◽  
Author(s):  
Alfred Strickholm ◽  
B. Gunnar Wallin
Keyword(s):  
Membrane Potential ◽  
Potassium Level ◽  
Potassium Concentration ◽  
Giant Axon ◽  
Resting Potential ◽  
Resting Membrane Potential ◽  
Constant Field ◽  
Appreciable Effect ◽  
Ion Concentrations ◽  
External Potassium

The changes in membrane potential of isolated, single crayfish giant axons following rapid shifts in external ion concentrations have been studied. At normal resting potential the immediate change in membrane potential after a variation in external potassium concentration is quite marked compared to the effect of an equivalent chloride change. If the membrane is depolarized by a maintained potassium elevation, the immediate potential change due to a chloride variation becomes comparable to that of an equivalent potassium change. There is no appreciable effect on membrane potential when external sodium is varied, at normal or at a depolarized membrane potential. Starting from the constant field equation, expressions for the permeability ratios PCl/PK, PNa/PK, and for intracellular potassium and chloride concentrations are derived. At normal resting membrane potential, PCl/PK is 0.13 but at a membrane potential of -53 mv (external potassium level increased about five times) it is 0.85. The intracellular concentrations of potassium and chloride are estimated to be 233 and 34 mM, respectively, and it is pointed out that this is not compatible with ions distributed in a Nernst equilibrium across the membrane. It is also stressed that the information given by a plot of membrane potential vs. the logarithm of external potassium concentrations is very limited and rests upon several important assumptions.

scholarly journals Effect of acetylcholine on postjunctional membrane permeability in eel electroplaque.

1977 ◽  
Vol 70 (1) ◽  
pp. 23-36 ◽  
Author(s):  
N L Lassignal ◽  
A R Martin
Keyword(s):  
Field Equation ◽  
Membrane Potential ◽  
Membrane Permeability ◽  
Ionic Composition ◽  
Reversal Potential ◽  
Resting Potential ◽  
Constant Field ◽  
Free Solution ◽  
Positive Direction ◽  
External K

Acetylcholine (ACh) was applied iontophoretically to the innervated face of isolated eel electroplaques while the membrane potential was being recorded intracellularly. At the resting potential (about -85 mV) application of the drug produced depolarizations (ACh potentials) of 20 mV or more which became smaller when the membrane was depolarized and reversed in polarity at about zero membrane potential. The reversal potential shifted in the negative direction when external Na+ was partially replaced by glucosamine. Increasing external K+ caused a shift of reversal potential in the positive direction. It was concluded that ACh increased the permeability of the postjunctional membrane to both ions. Replacement of Cl- by propionate had no effect on the reversal potential. In Na+-free solution containing glucosamine the reversal potential was positive to the resting potential, suggesting that ACh increased the permeability to glucosamine. Addition of Ca++ resulted in a still more positive reversal potential, indicating an increased permeability to Ca++ as well. Analysis of the results indicated that the increases in permeability of the postjunctional membrane to K+, Na+, Ca++, and glucosamine were in the ratios of approximately 1.0:0.9:0.7:0.2, respectively. With these permeability ratios, all of the observed shifts in reversal potential with changes in external ionic composition were predicted accurately by the constant field equation.

Effect of procaine on electrical properties of squid axon membrane

1959 ◽  
Vol 196 (5) ◽  
pp. 1071-1078 ◽  
Author(s):  
Robert E. Taylor
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Electrical Properties ◽  
Potassium Conductance ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Squid Axon ◽  
Voltage Step ◽  
Axon Membrane ◽  
Rate Of Development

Procaine (0.025–0.1%; pH 7.9) caused a reduction in the amount and rate of development of the early transient (sodium) and late steady state (potassium) currents which occur during a depolarizing voltage step applied to the excised, voltage clamped squid axon. Consistent results were obtained by holding the membrane potential at a hyperpolarized value prior to the applied step. No effect was seen on the resting potential, on the sodium equilibrium potential, or on the proportion of the sodium carrying system which was ‘inactive’ at any membrane potential. The blocking action of procaine is a result of the inhibition by the drug of the sodium carrying system. The effect of procaine on the potassium conductance is such as to oppose the blocking action.

scholarly journals RUBIDIUM AND CESIUM FLUXES IN MUSCLE AS RELATED TO THE MEMBRANE POTENTIAL

1959 ◽  
Vol 42 (5) ◽  
pp. 983-1003 ◽  
Author(s):  
Raymond A. Sjodin
Keyword(s):  
Field Theory ◽  
Membrane Potential ◽  
Low Temperatures ◽  
Resting Potential ◽  
Sartorius Muscle ◽  
Potassium Ions ◽  
Constant Field ◽  
Cesium Ions ◽  
Potassium Flux ◽  
Frog Sartorius

The reduction of membrane potential in frog sartorius muscle produced by rubidium and cesium ions has been studied over a wide concentration range and compared with depolarization occasioned by potassium ions. The constant field theory of passive flux has been used to predict the potential changes observed. The potential data suggest certain permeability coefficient ratios and these are compared with ratios obtained from flux data using radioactive tracers. The agreement of the flux with the potential data is good if account is taken of the inhibition of potassium flux which occurs in the presence of rubidium and cesium ions. A high temperature dependence has been observed for cesium influx (Q10 = 2.5) which is correlated with the observation that cesium ions depolarize very little at low temperatures. The observations suggest that cesium ions behave more like sodium ions at low temperatures and more like potassium ions at room temperature with respect to their effect on the muscle cell resting potential. The constant field theory of passive ion flux appears to be in general agreement with the experimental results observed if account is taken of the dependence of permeability coefficients on the concentrations of ions used and of possible interactions between the permeabilities of ions.

The influence of voltage conditioning on chloride currents in amphibian muscle membrane: the sigmoid conductance–voltage relation extended into the outward current region

1982 ◽  
Vol 60 (5) ◽  
pp. 604-609 ◽  
Author(s):  
Peter Vaughan ◽  
Martin Trotter
Keyword(s):  
Outward Current ◽  
Positive Test ◽  
Resting Potential ◽  
Muscle Membrane ◽  
Delayed Rectifier ◽  
Sartorius Muscle ◽  
Muscle Fibres ◽  
Initial Current ◽  
Chloride Currents ◽  
Delayed Rectifier Current

Sartorius muscle fibres of Xenopus laevis were depolarized in solutions of high K+ content and then voltage clamped in solutions in which K+ was replaced by Rb+ and(or) tetraethylammonium ion (TEA+) at pH 9. A three-microelectrode clamp system was used in which the bath was held at virtual ground using an operational amplifier in a current meter configuration. The holding potential was set at zero membrane current potential (resting potential), close to −25 mV. A two-pulse paradigm was used to test the effects of conditioning the membrane at voltages away from the resting potential on initial currents at positive test potentials. In the absence of TEA+ rapidly rising outward currents were generated at positive test potentials, following hyperpolarizing conditioning. These currents inactivated in time and obscured predicted chloride currents. When TEA+ was added to the solution (60 mequiv./L) the currents at positive potentials rose more slowly and declined either very slowly or not at all. Projection of these current waveforms, by curve fitting, to the instant of potential change gave a sigmoid dependence of test current on conditioning voltage that was predicted from earlier results. Predictably there is a test voltage at which the initial current is independent of conditioning potential: from the data it appears that this is not necessarily the resting potential, but the cause of the shift is not clear. The results also indicated that there is a component of outward current that is very small, apparently earned by cations ("delayed rectifier current"), that does not inactivate, even at potentials more positive than the resting potential.

Two Types of Intrinsic Oscillations in Neurons of the Lateral and Basolateral Nuclei of the Amygdala

1998 ◽  
Vol 79 (1) ◽  
pp. 205-216 ◽  
Author(s):  
Hans-Christian Pape ◽  
Denis Paré ◽  
Robert B. Driesang
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Resting Potential ◽  
Oscillatory Activity ◽  
Negative Slope ◽  
High Threshold ◽  
Projection Neurons ◽  
Membrane Polarization ◽  
Low Threshold ◽  
Rhythmic Firing

Pape, Hans-Christian, Denis Paré, and Robert B. Driesang. Two types of intrinsic oscillations in neurons of the lateral and basolateral nuclei of the amygdala. J. Neurophysiol. 79: 205–216, 1998. Intracellular recordings in the guinea pig and cat basolateral amygdaloid (BL) complex maintained as slices in vitro revealed that a subpopulation of neurons (79%) in the lateral (AL) and basolateral (ABl) nuclei generated two types of slow oscillations of the membrane potential upon steady depolarization from resting potential. The cells were of a stellate or pyramidal-like shape and possessed spiny dendrites and an axon leaving the local synaptic environment, and thus presumably represented projection neurons. Similar oscillatory activity was observed in projection neurons of the cat AL nucleus recorded in vivo. Oscillatory activity with a low threshold of activation (low-threshold oscillation, LTO) appeared as rhythmic deflections (amplitudes, 2–6 mV) of the membrane potential positive to −60 mV. Fast Fourier transformation (FFT) demonstrated a range of frequencies of LTOs between 0.5 and 9 Hz, with >80% occurring at 1–3.5 Hz and an average at 2.3 ± 1.1 Hz. LTOs were more regular after pharmacological blockade of synaptic transmission and were blocked by tetrodotoxin (TTX). Blockade of LTOs and Na+ spikes revealed a second type of oscillatory activity (high-threshold oscillation, HTO) at depolarizations beyond −40 mV, which was capable of triggering high-threshold spikes. HTOs ranged between 1 and 7.5 Hz, with >80% occurring at 2–6 Hz and an average at 5.8 ± 1.1 Hz. HTOs vanished at a steady membrane polarization positive to −20 mV. Current versus voltage relations obtained under voltage-clamp conditions revealed two regions of negative slope conductance at −55 to −40 mV and at around −30 mV, which largely overlapped with the voltage ranges of LTOs and HTOs. TTX abolished the first region of negative slope conductance (−55 to −40 mV) and did not significantly influence the second region of negative slope conductance. Neuronal responses to maintained depolarizing current pulses consisted of an initial high-frequency discharge (up to 100 Hz), the frequency of which depended on the amplitude of the depolarizing current pulse, followed by a progressive decline (“adaptation”) toward a slow-rhythmic firing pattern. The decay in firing frequency followed a double-exponential function, with time constants averaging 57 ± 28 ms and 3.29 ± 1.85 s, and approached steady-state frequencies at 6.3 ± 2.9 Hz ( n = 17). Slow-rhythmic firing remained at this frequency over a wide range of membrane polarization between approximately −50 and −20 mV, although individual electrogenic events changed from Na+ spikes and underlying LTOs to high-threshold spikes and underlying HTOs. Rhythmic regular firing was only interrupted at an intermediate range of membrane polarization by the occurrence of spike doublets. In conclusion, the integrative behavior of a class of neurons in the BL complex appears to be largely shaped by the slow-oscillatory properties of the membrane. While LTOs are likely to synchronize synaptic signals near firing threshold, HTOs are a major determinant for the slow steady-state firing patterns during maintained depolarizing influence. These intrinsic oscillatory mechanisms, in turn, can be assumed to promote population activity at this particular frequency, which ranges well within that of the limbic theta (Θ) rhythm and the delta (δ) waves in the electroencephalogram during slow-wave sleep.

Visual adaptation modulates a potassium conductance in retinular cells of the crayfish

2000 ◽  
Vol 17 (3) ◽  
pp. 353-368 ◽  
Author(s):  
C.S. MILLER ◽  
R.M. GLANTZ
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Light Exposure ◽  
Potassium Conductance ◽  
Visual Sensitivity ◽  
Calcium Currents ◽  
Resting Potential ◽  
Delayed Rectifier ◽  
Dependent Change ◽  
Retinular Cells

Crayfish photoreceptors exhibit a voltage-dependent potassium conductance, GK, that is generally similar to the delayed rectifier channel described in neurons and other arthropod retinular cells. GK activation (i.e. the apparent threshold, Vth) occurs near the resting potential and GK is substantially reduced by 25 mM extracellular tetraethylammonium (TEA) and by intracellular Cs+ injections. Light exposure, sufficient to reduce visual sensitivity 100-fold, increases Vth (shifts it in the depolarizing direction) by about 20 mV. The light-dependent change in Vth does not depend upon the corresponding increase (depolarization) of the steady-state membrane potential nor does it depend upon inward calcium currents. Vth is slightly influenced by fluctuations in Ko associated with the light-elicited currents. During light exposure Ko (measured with K+-sensitive electrodes) increases by 2.1 mM (equivalent to an 8 mV increase in EK). This increase in EK makes only a modest contribution to the light-dependent change in Vth as determined by perfusion with high potassium salines. Intracellular calcium injections increase Vth by 10 to 20 mV and reduce visual sensitivity by 5- to 10-fold. The results imply that during exposure to high levels of illumination, K+ currents at the steady-state membrane potential are diminished by a calcium-dependent change in GK gating and, to a smaller degree, by a reduced K+ concentration gradient. It is notable that Ca2+ appears to inhibit both GK and the light-elicited conductance from both inside and outside the plasma membrane. As a consequence of the light-dependent change in Vth, GK makes only modest contributions to the changes in sensitivity and speed normally associated with light adaption. These functions are regulated by the transduction pathway and are revealed at the resting potential in the time course and magnitude of the light-elicited currents.

Effects of epinephrine on resting potential in normal and hypertrophied cardiac muscles

1983 ◽  
Vol 245 (1) ◽  
pp. H90-H97
Author(s):  
S. R. Houser ◽  
V. Burgis ◽  
F. Martin ◽  
D. Weinberg
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Cardiac Muscle ◽  
Resting Potential ◽  
Papillary Muscles ◽  
Ion Balance ◽  
Rates Of Change ◽  
Cardiac Muscles ◽  
K Activity

The role of the Na-K pump in the control of cellular ion balance has long been appreciated. Recent studies suggest that the manner in which this ion transport system functions in hypertrophied failing (HF) cardiac muscle is markedly different from that seen in normal muscles. The ability of the sympathetic neurohormone, epinephrine, to modulate membrane potential changes thought to reflect the activity of the Na-K pump in normal and HF cardiac muscle was examined in this study. Specifically rate-related changes in membrane potential (Emax) thought to be associated with the Na-K pump were measured in intact functioning cat papillary muscles. The results of these studies demonstrate that the rate-related changes in Emax thought to be associated with Na-K activity were markedly altered in HF cardiac muscles. Emax in these muscles responded to periods of transient stimulation by first depolarizing and then slowly returning to a new steady state which was depolarized with respect to the initial predrive Emax. Emax in normal muscles also depolarized on drive, but returned to a new steady state more rapidly and eventually hyperpolarized. Epinephrine significantly affected these rate-related changes in Emax in normal muscles by causing all the rates of change in Emax to be increased. In HF muscles, on the other hand, epinephrine had no significant effect on these parameters at the concentration tested. These results suggest that under certain conditions HF cardiac muscle may be incapable of maintaining normal resting membrane potentials. In addition the modulating influence of epinephrine is markedly blunted.

Slow inactivation of a TEA-sensitive K current in acutely isolated rat thalamic relay neurons

1991 ◽  
Vol 66 (4) ◽  
pp. 1316-1328 ◽  
Author(s):  
J. R. Huguenard ◽  
D. A. Prince
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Outward Current ◽  
Resting Potential ◽  
Transient Outward Current ◽  
Voltage Range ◽  
Voltage Dependent ◽  
Kinetics Of ◽  
K Currents ◽  
Relay Neurons

1. Voltage-gated K currents were studied in relay neurons (RNs) acutely isolated from somatosensory (VB) thalamus of 7- to 14-day-old rats. In addition to a rapidly activated, transient outward current, IA, depolarizations activated slower K+ currents, which were isolated through the use of appropriate ionic and pharmacological conditions and measured via whole-cell voltage-clamp. 2. At least two slow components of outward current were observed, both of which were sensitive to changes in [K+]o, as expected for K conductances. The first, IK1, had an amplitude that was insensitive to holding potential and a relatively small conductance of 150 pS/pF. It was blocked by submillimolar levels of tetraethylammonium [TEA, 50%-inhibitory concentration (IC50 = 30 microM)] and 4-aminopyridine (4-AP, 40 microM). In the absence of intracellular Ca2+ buffering, the amplitude of IK1 was both larger and dependent on holding potential, as expected for a Ca(2+)-dependent current. Replacement of [Ca2+]o by Co2+ reduced IK1, although the addition of Cd2+ to Ca(2+)-containing solutions had no effect. 3. The second component, IK2, had a normalized conductance of 2.0 nS/pF and was blocked by millimolar concentrations of TEA (IC50 = 4 mM) but not by 4AP. The kinetics of IK2 were analogous to (but much slower than) those of IA in that both currents displayed voltage-dependent activation and voltage-independent inactivation. IK2 was not reduced by the addition of Cd2+ to Ca(2+)-containing solutions or by replacement of Ca2+ by Co2+. 4. IK2 had a more depolarized activation threshold than IA and attained peak amplitude with a latency of approximately 100 ms at room temperature. IK2 decay was nonexponential and could be described as the sum of two components with time constants (tau) near 1 and 10 s. 5. IK2 was one-half steady-state inactivated at a membrane potential of -63 mV, near the normal resting potential for these cells. The slope factor of the Boltzman function describing steady-state inactivation was 13 mV-1, which indicates that IK2 varies in availability across a broad voltage range between -100 and -20 mV. 6. Activation kinetics of IK2 were voltage dependent, with peak latency shifting from 300 to 50 ms in the voltage range -50 to +30 mV. Deinactivation and deactivation were also voltage dependent, in contrast to inactivation, which showed little dependence on membrane potential. Increase in temperature sped the kinetics of IK2, with temperature coefficient (Q10) values near 3 for activation and inactivation. Heating increased the amplitude of IK2 with a Q10 value near 2.(ABSTRACT TRUNCATED AT 400 WORDS)

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