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.

COMPARISON BETWEEN THERMORECEPTOR AND MECHANORECEPTOR CURRENTS IN PARAMECIUM CAUDATUM

1994 ◽  
Vol 189 (1) ◽  
pp. 117-131 ◽  
Author(s):  
T Tominaga ◽  
Y Naitoh
Keyword(s):  
Membrane Potential ◽  
Reversal Potential ◽  
Mechanical Stimulus ◽  
Membrane Current ◽  
Resting Potential ◽  
Sign Reversal ◽  
Positive Direction ◽  
Algebraic Summation ◽  
Stimulation Of ◽  
External K

1. A voltage-clamped Paramecium produced an inward membrane current upon thermal or mechanical stimulation of its anterior region, whereas it produced an outward membrane current upon similar stimulation of its posterior region. 2. Anterior thermo- and mechanoreceptor currents decreased when the membrane potential was shifted in a positive direction, showing sign reversal at a positive membrane potential, whereas posterior thermo- and mechanoreceptor currents decreased when the membrane potential was shifted in a negative direction, showing sign reversal at a membrane potential more negative than the resting potential. 3. The reversal potential for both anterior receptor currents shifted in a positive direction when external [Ca2+] was increased, whereas those for both posterior receptor currents shifted in a positive direction when external [K+] was increased. 4. External [Mg2+], [Mn2+], [Na+], [Rb+] and [TEA+] had similar effects on the thermo- and mechanoreceptor currents. 5. Thermoreceptor currents decreased whereas mechanoreceptor currents increased as the ambient temperature was raised. 6. When a mechanical stimulus was applied to the membrane where a thermoreceptor current was being produced, an algebraic summation of these receptor currents occurred. 7. It is concluded that thermoreceptor currents are dependent on ion channels different from those responsible for the mechanoreceptor currents, although the ionic pores for the channels are similar to each other in various respects. 8. A possibility that a thermoreceptor mechanism exclusively shares a Ca2+ pore in the anterior membrane, or a K+ pore in the posterior membrane, with a mechanoreceptor mechanism is discussed.

Voltage-clamp analysis of currents produced by glutamate and some glutamate analogues on horizontal cells isolated from the catfish retina

1986 ◽  
Vol 56 (1) ◽  
pp. 19-31 ◽  
Author(s):  
G. Hals ◽  
B. N. Christensen ◽  
T. O'Dell ◽  
M. Christensen ◽  
R. Shingai
Keyword(s):  
Membrane Potential ◽  
Amino Acid ◽  
Membrane Permeability ◽  
Time Course ◽  
Reversal Potential ◽  
Horizontal Cells ◽  
Resting Potential ◽  
Bathing Solution ◽  
Patch Type ◽  
Highly Nonlinear

Horizontal cells isolated from the catfish retina were exposed to radiolabeled glutamate, glycine, gamma-aminobutyric acid (GABA), and sucrose to determine if the enzymatic dissociation procedure altered the high-affinity uptake mechanism for GABA and generally reduced membrane selectivity. As in the intact retina, isolated cells could transport GABA but not the other substances. The horizontal cells were voltage clamped using a single low-resistance patch-type electrode. The acidic amino acid L-glutamate, and its analogues kainate and quisqualate, were applied to the cell by pressure ejection from a nearby pipette. All three agonists produced inward currents that reversed near O mV. Quisqualate produced a current with a similar time course as glutamate, but the time course of the response to kainate was faster. The agonists N-methyl-D-aspartate and L-aspartate had little effect on the membrane conductance. The current-to-voltage (I-V) relationship for all three agonists was nonlinear when the membrane potential was hyperpolarized. The nonlinearity was, at least in part, a result of the decreased response to the three agonists. Removal of Mg did not alter this nonlinear relationship. When the inward potassium rectifier was blocked with 100 microM Ba, the response to glutamate was increased compared with the control experiment before block by barium; however, the I-V relationship was still highly nonlinear. Thus glutamate block of the inward potassium current cannot account entirely for the nonlinear I-V. The increase in membrane permeability to specific ions in the presence of an agonist was determined by ion substitution experiments and measuring the shift in the reversal potential. The three agonists appear to increase the membrane permeability to cations but not to anions. The amino acid antagonists cis-2,3-piperidine dicarboxylic acid (PDA) and D-glutamyl glycine (DGG) were bath applied to test their ability to block the depolarizing effects of glutamate. DGG had no measureable effect at 100 microM concentration, whereas PDA reversibly reduced the glutamate response at 1 mM concentration although block was incomplete. Isolated horizontal cells responded to bath-applied glutamate in concentrations of 10-500 microM. In concentrations of glutamate greater than 50 microM, when the membrane potential was held at the resting potential, the inward current reached a maximum followed by a decrease to a steady-state level. This apparent time-dependent desensitization at high agonist concentrations was at least partially removed when Mg was removed from the bathing solution.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals A classic experiment revisited: membrane permeability changes during the action potential

2021 ◽  
Vol 45 (1) ◽  
pp. 178-181
Author(s):  
Carolyn L. Powell ◽  
Angus M. Brown
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Membrane Permeability ◽  
Reversal Potential ◽  
Resting Potential ◽  
Membrane Excitability ◽  
Permeability Changes ◽  
The Relationship ◽  
Potential Peak ◽  
Three Phases

The ability to understand the relationship between the reversal potential and the membrane potential is a fundamental skill that must be mastered by students studying membrane excitability. To clarify this relationship, we have reframed a classic experiment carried out by Hodgkin and Katz, where we compare graphically the membrane potential at three phases of the action potential (resting potential, action potential peak, and afterhyperpolarization) to reversal potential for K+ ( EK), reversal potential for Na ( ENa), and membrane potential ( Em) (calculated by the Goldman Hodgkin Katz equation) to illustrate that the membrane potential approaches the reversal potential of the ion to which it is most permeable at that instant.

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.

An Investigation of the Electrogenic Sodium Pump in Snail Neurones, Using the Constant-Field Theory

1969 ◽  
Vol 51 (1) ◽  
pp. 181-201
Author(s):  
R. B. MORETON
Keyword(s):  
Field Equation ◽  
Sodium Pump ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Constant Field ◽  
Sodium Ions ◽  
Intracellular Potassium ◽  
Electrogenic Sodium Pump ◽  
Snail Neurones ◽  
Intracellular Potassium Concentration

1. Sodium ions injected into giant neurones of Helix aspersa by diffusion from low-resistance microelectrodes caused hyperpolarization of the cells. Under these conditions the behaviour of the resting potential could be described by a modified ‘constant-field’ equation, including a term representing the effect of a potassiumsensitive, electrogenic sodium pump. 2. Exposure to potassium-free solution, ouabain or cyanide abolished the hyperpolarization, and caused a gradual fall in the intracellular potassium concentration, as estimated from the constant-field equation. 3. Assuming that this fall was due to replacement of intracellular potassium by injected sodium ions, it was possible to calculate the rates of injection and pumping of sodium ions, and, using the measured membrane resistance of the cell, the hyperpolarization which the sodium pump could cause, if it were electrogenic. 4. This was related to the observed hyperpolarization, supporting the view that the latter was caused by stimulation of the electrogenic sodium pump.

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.

Control of intracellular calcium by membrane potential in human melanoma cells

1993 ◽  
Vol 265 (6) ◽  
pp. C1501-C1510 ◽  
Author(s):  
B. Nilius ◽  
G. Schwarz ◽  
G. Droogmans
Keyword(s):  
Cell Proliferation ◽  
Membrane Potential ◽  
Intracellular Calcium ◽  
Reversal Potential ◽  
Melanoma Cells ◽  
Human Melanoma ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Patch Clamp Technique ◽  
Human Melanoma Cells

The modulation of intracellular calcium ([Ca2+]i) by the membrane potential was investigated in human melanoma cells by combining the nystatin-perforated patch-clamp technique with Ca2+ measurements. Voltage steps to -100 mV induced a rise in [Ca2+]i and a creeping inward current. These effects were absent in Ca(2+)-free solution and could be blocked by Ni2+ or La3+. Voltage ramps revealed a close correlation between [Ca2+]i and voltage, with the strongest voltage dependence around the resting potential. Long-lasting tail currents, closely correlated with the rise in [Ca2+]i and a reversal potential close to the K+ equilibrium potential, occurred if the membrane potential was clamped back to 0 mV. They were absent if intracellular K+ was replaced by Cs+ and blocked by extracellular tetraethylammonium (5 mM), Ba2+ (1 mM), or a membrane-permeable adenosine 3',5'-cyclic monophosphate analogue. These observations are discussed in relation to cell proliferation. The enhanced expression of K+ channels during cell proliferation provides a positive-feedback mechanism resulting in long-term changes in [Ca2+]i required for the G1-S transition in the cell cycle.

Modification of Current Transmitted From Apical Dendrite to Soma by Blockade of Voltage- and Ca2+-Dependent Conductances in Rat Neocortical Pyramidal Neurons

1997 ◽  
Vol 78 (1) ◽  
pp. 187-198 ◽  
Author(s):  
Peter C. Schwindt ◽  
Wayne E. Crill
Keyword(s):  
Membrane Potential ◽  
Pyramidal Neurons ◽  
Reversal Potential ◽  
Apical Dendrite ◽  
Axial Current ◽  
Resting Potential ◽  
High Threshold ◽  
Voltage Gated ◽  
Distal Site ◽  
Neocortical Pyramidal Neurons

Schwindt, Peter C. and Wayne E. Crill. Modification of current transmitted from apical dendrite to soma by blockade of voltage- and Ca2+-dependent conductances in rat neocortical pyramidal neurons. J. Neurophysiol. 78: 187–198, 1997. The axial current transmitted to the soma during the long-lasting iontophoresis of glutamate at a distal site on the apical dendrite was measured by somatic voltage clamp of rat neocortical pyramidal neurons. Evidence for voltage- and Ca2+-gated channels in the apical dendrite was sought by examining the modification of this transmitted current resulting from the alteration of membrane potential and the application of channel-blocking agents. After N-methyl-d-aspartate receptor blockade, iontophoresis of glutamate on the soma evoked a current whose amplitude decreased linearly with depolarization to an extrapolated reversal potential near 0 mV. Under the same conditions, glutamate iontophoresis on the apical dendrite 241–537 μm from the soma resulted in a transmitted axial current that increased with depolarization over the same range of membrane potential (about −90 to −40 mV). Current transmitted from dendrite to soma was thus amplified during depolarization from resting potential (about −70 mV) and attenuated during hyperpolarization. After Ca2+ influx was blocked to eliminate Ca2+-dependent K+ currents, application of 10 mM tetraethylammonium chloride (TEA) altered the amplitude and voltage dependence of the transmitted current in a manner consistent with the reduction of dendritic voltage-gated K+ current. We conclude that dendritic, TEA-sensitive, voltage-gated K+ channels can be activated by tonic dendritic depolarization. The most prominent effects of blocking Ca2+ influx resembled those elicited by TEA application, suggesting that these effects were caused predominantly by blockade of a dendritic Ca2+-dependent K+ current. When cells were impaled with microelectrodes containing ethylene glycol-bis(β-amino-ethyl ether)- N,N′,N′-tetraacetic acid to prevent a rise in intracellular Ca2+ concentration, blockade of Ca2+ influx altered the tonic transmitted current in different manner consistent with the blockade of a inward dendritic current carried by high-threshold-activated Ca2+ channels. We conclude that the primary effect of Ca2+ influx during tonic dendritic depolarization is the activation of a dendritic Ca2+-dependent K+ current. The hyperpolarizing attenuation of transmitted current was unaffected by blocking all known voltage-gated inward currents except the hyperpolarization-activated cation current ( I h). Extracellular Cs+ (3 mM) reversibly abolished both the hyperpolarizing attenuation of transmitted current and I h measured at the soma. We conclude that activation of I h by hyperpolarization of the proximal apical dendrite would cause less axial current to arrive at the soma from a distal site than in a passive dendrite. Several functional implications of dendritic K+ and I h channels are discussed.

The diffusion and electrogenic components of the membrane potential of hypoxic myocardium

1987 ◽  
Vol 65 (2) ◽  
pp. 246-251 ◽  
Author(s):  
Normand Leblanc ◽  
Elena Ruiz-Ceretti
Keyword(s):  
Membrane Potential ◽  
Sodium Pump ◽  
Resting Potential ◽  
Krebs Solution ◽  
Ventricular Muscle ◽  
Diffusion Component ◽  
K Concentration ◽  
Zero Potential ◽  
K Permeability ◽  
External K

The diffusion and electrogenic components of the resting potential of hypoxic ventricular muscle were separated by inhibition of the sodium pump with 10−4 M ouabain. The response to varying external K concentrations (Ko) was studied. Arteriaily perfused rabbit hearts were submitted to 60 min hypoxia in Krebs solution containing 5 mM K throughout or to different external K concentrations during the last 20 min of hypoxia. For K concentrations between 1.5 and 10 mM, hypoxia did not change the resting potential except for a slight hyperpolarization in 7.5 mM K. The diffusion component of the resting potential did not differ from the resting potential at Ko < 5 mM. An electrogenic potential of −3 to −6 mV was detectable at Ko values between 5 and 10 mM. The internal K concentration, Ki, was estimated from extrapolations to zero potential of the relation resting potential vs. Ko in normoxic and hypoxic hearts. These experiments revealed a decline of Ki of 16 mM with hypoxia. The variation of the diffusion potential with external K was fitted by a PNa:PK ratio five times lower than in normoxia. It has been concluded that an increase in K permeability and the persistence of electrogenic Na extrusion during hypoxia of rather short duration prevent membrane depolarization despite the myocardial K loss.

scholarly journals The light-sensitive conductance of hyperpolarizing invertebrate photoreceptors: a patch-clamp study.

1994 ◽  
Vol 103 (6) ◽  
pp. 939-956 ◽  
Author(s):  
M P Gomez ◽  
E Nasi
Keyword(s):  
Single Channel ◽  
Light Stimulus ◽  
Divalent Cations ◽  
Reversal Potential ◽  
Outward Current ◽  
Membrane Conductance ◽  
Resting Potential ◽  
Light Stimulation ◽  
Positive Direction ◽  
Single Channel Currents

Tight-seal recording was employed to investigate membrane currents in hyperpolarizing ciliary photoreceptors enzymatically isolated from the eyes of the file clam (Lima scabra) and the bay scallop (Pecten irradians). These two organisms are unusual in that their double retinas also possess a layer of depolarizing rhabdomeric cells. Ciliary photoreceptors from Lima have a rounded soma, 15-20 microns diam, and display a prominent bundle of fine processes up to 30 microns long. The cell body of scallop cells is similar in size, but the ciliary appendages are modified, forming small spherical structures that protrude from the cell. In both species light stimulation at a voltage near the resting potential gives rise to a graded outward current several hundred pA in amplitude, accompanied by an increase in membrane conductance. The reversal potential of the photocurrent is approximately -80 mV, and shifts in the positive direction by approximately 39 mV when the concentration of extracellular K is increased from 10 to 50 mM, consistent with the notion that light activates K-selective channels. The light-activated conductance increases with depolarization in the physiological range of membrane voltages (-30 to -70 mV). Such outward rectification is greatly reduced after removal of divalent cations from the superfusate. In Pecten, cell-attached recordings were also obtained; in some patches outwardly directed single-channel currents could be activated by light but not by voltage. The unitary conductance of these channels was approximately 26 pS. Solitary ciliary cells also gave evidence of the post stimulus rebound, which is presumably responsible for initiating the "off" discharge of action potentials at the termination of a light stimulus: in patches containing only voltage-dependent channels, light stimulation suppressed depolarization-induced activity, and was followed by a strong burst of openings, directly related to the intensity of the preceding photostimulation.

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