The effect of displacement current on the measurement of reversal potential in squid giant axon

1982 ◽  
Vol 60 (12) ◽  
pp. 1541-1544 ◽  
Author(s):  
H. Wodlinger ◽  
H. Kunov ◽  
H. L. Atwood
Keyword(s):  
Voltage Clamp ◽  
Time Constant ◽  
Reversal Potential ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Displacement Current ◽  
Before And After

The measurement of the sodium reversal potential (Erev), as that potential where the early current reverses during voltage clamp, was found to exceed the true Erev by 4.1 ± 2.4 mV (mean ± SD) in squid giant axon. This error was found in both intact and internally perfused axons and is due to interference from the displacement current. This was shown by subtraction of the current records obtained before and after treatment with tetrodotoxin (TTX). The error in Erev is proportional to [Formula: see text] where Td is the time constant of the displacement current.

scholarly journals Sodium influxes in internally perfused squid giant axon during voltage clamp

1969 ◽  
Vol 201 (3) ◽  
pp. 657-664 ◽  
Author(s):  
I. Atwater ◽  
F. Bezanilla ◽  
E. Rojas
Keyword(s):  
Voltage Clamp ◽  
Giant Axon ◽  
Squid Giant Axon

Calcium current in squid giant axon

1975 ◽  
Vol 270 (908) ◽  
pp. 377-387 ◽  
Keyword(s):  
Sodium Channel ◽  
Voltage Clamp ◽  
Reversal Potential ◽  
Outward Current ◽  
External Solution ◽  
Giant Axon ◽  
Constant Field ◽  
Field Equations ◽  
Tetraethylammonium Chloride ◽  
Inward Current

Voltage-clamp experiments were carried out on intracellularly perfused squid giant axons in a Na-free solution of 100 mM CaCl 2 + sucrose. The internal solution was 25 mM CsF + sucrose or 100 mM RbF + 50 mM tetraethylammonium chloride + sucrose. Depolarizing voltage clamp steps produced small inward currents; at large depolarizations the inward current reversed into an outward current. Tetrodotoxin completely blocked the inward current and part of the outward current. No inward current was seen with 100 mM MgCl 2 + sucrose as external solution. It is concluded that the inward current is carried by Ca ions moving through the sodium channel. The reversal potential of the tetrodotoxin-sensitive current was + 54 mV with 25 mM CsF + sucrose inside and +10 mV with 100 mM RbF + 50 mM tetraethylammonium chloride + sucrose inside. From the reversal potentials measured with varying external and internal solutions the relative permeabilities of the sodium channel for Ca, Cs and Na were calculated by means of the constant field equations. The results of the voltage-clamp experiments are compared with measurements of the Ca entry in intact axons.

scholarly journals Time course of the sodium influx in squid giant axon during a single voltage clamp pulse

1970 ◽  
Vol 207 (1) ◽  
pp. 151-164 ◽  
Author(s):  
Francisco Bezanilla ◽  
Eduardo Rojas ◽  
Robert E. Taylor
Keyword(s):  
Voltage Clamp ◽  
Time Course ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Sodium Influx

scholarly journals LOW LEVEL IMPEDANCE CHANGES FOLLOWING THE SPIKE IN THE SQUID GIANT AXON BEFORE AND AFTER TREATMENT WITH "VERATRINE" ALKALOIDS

1953 ◽  
Vol 37 (1) ◽  
pp. 39-51 ◽  
Author(s):  
Abraham M. Shanes ◽  
Harry Grundfest ◽  
Walter Freygang
Keyword(s):  
Sea Water ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Satisfactory Explanation ◽  
Chloride Permeability ◽  
Potential Oscillations ◽  
Temporal Course ◽  
Before And After ◽  
Conductance Changes ◽  
Conductance Increase

The increase in conductance, which accompanies the spike in the presence of sea water, is followed by a decrease to below the resting level, here designated as the "initial after-impedance," which lasts 3 msec. and is 3 per cent as great as the increase. Treatment with cevadine usually obliterates the latter but leaves the former essentially unaltered. In addition, the alkaloid gives rise to periodic conductance increases followed by a prolonged, exponentially decaying elevated conductance (the "negativity after-impedance") which correspond closely to potential oscillations and to the negative after-potential. These are also only a few per cent of the major conductance change. Veratridine causes a conductance increase which lasts longer and which also conforms closely with earlier after-potential results. Preliminary calculations indicate that the negativity after-impedance and the negative after-potential may be due to the subsidence of an elevated chloride permeability. However, no satisfactory explanation is available for the initial after-impedance or for the temporal course of the conductance changes associated with oscillations in membrane potential.

scholarly journals THE EFFECT OF SODIUM AND POTASSIUM IONS ON THE IMPEDANCE CHANGE ACCOMPANYING THE SPIKE IN THE SQUID GIANT AXON

1953 ◽  
Vol 37 (1) ◽  
pp. 25-37 ◽  
Author(s):  
Harry Grundfest ◽  
Abraham M. Shanes ◽  
Walter Freygang
Keyword(s):  
Voltage Clamp ◽  
Potassium Level ◽  
Giant Axon ◽  
Sodium Concentration ◽  
Squid Giant Axon ◽  
Potassium Ions ◽  
Impedance Change ◽  
Voltage Clamp Technique ◽  
Sodium And Potassium ◽  
Identical Fashion

Decrease of the sodium concentration of the medium depresses both the spike and the associated impedance change in almost identical fashion. Elevation of the potassium level also depresses both phenomena, but affects the impedance change more than the spike; it slows the return to the initial impedance level. The effects on the threshold to brief square waves are also described. These results appear largely accounted for by the observations of Hodgkin and Huxley with the voltage clamp technique and by their recent hypothesis as to nature of the spike processes.

Kinetics of activation of the potassium conductance in the squid giant axon

1988 ◽  
Vol 232 (1269) ◽  
pp. 375-394 ◽  
Keyword(s):  
Time Constant ◽  
Potassium Current ◽  
Time Course ◽  
Potassium Conductance ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
A Value ◽  
Initial Rise ◽  
Principal Effect ◽  
Kinetics Of

A quantitative re-investigation of the time course of the initial rise of the potassium current in voltage-clamped squid giant axons is described. The n 4 law of the Hodgkin–Huxley equations was found to be well obeyed only for the smallest test pulses, and for larger ones a good fit of the inflected rise required use of the expression (1 – exp {– t / ז n 1 }) X –1 (1 – exp { – t / ז n 2 }), where both of the time constants and the power X varied with the size of the test pulse. Application of a negative prepulse produced a delay in the rise resulting mainly from an increase of X from a value of about 3 at –70 mV to 8 at –250 mV, while ז n 1 remained constant and ז n 2 was nearly doubled. The process responsible for generating this delay was switched on with a time constant of 8 ms at 4°C, which fell to about 1 ms at 15°C. Analysis of the inward tail currents at the end of a voltage-clamp pulse showed that there was a substantial external accumulation of potassium owing to the restriction of its diffusion out of the Schwann cell space, which, when duly allowed for, roughly doubled the calculated value of the potassium conductance. Computations suggested that the principal effect of such a build-up of [K] o would be to reduce the fitted values of ז n 1 and ז n 2 to two-thirds or even half their true sizes, while the power X would generally be little changed; but it would not affect the necessity to introduce a second time constant, nor would it invalidate our findings on the effect of negative prepulses.

scholarly journals Ammonium Ion Currents in the Squid Giant Axon

1969 ◽  
Vol 53 (3) ◽  
pp. 342-361 ◽  
Author(s):  
Leonard Binstock ◽  
Harold Lecar
Keyword(s):  
Voltage Clamp ◽  
Ammonium Chloride ◽  
Time Course ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Ammonium Ion ◽  
Ion Currents ◽  
Potassium Permeability ◽  
Nerve Excitability ◽  
Conductance Changes

Voltage-clamp studies on intact and internally perfused squid giant axons demonstrate that ammonium can substitute partially for either sodium or potassium. Ammonium carries the early transient current with 0.3 times the permeability of sodium and it carries the delayed current with 0.3 times the potassium permeability. The conductance changes observed in voltage clamp show approximately the same time course in ammonium solutions as in the normal physiological solutions. These ammonium ion permeabilities account for the known effects of ammonium on nerve excitability. Experiments with the drugs tetrodotoxin (TTX) and tetraethyl ammonium chloride (TEA) demonstrate that these molecules block the early and late components of the current selectively, even when both components are carried by the same ion, ammonium.

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