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 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.

scholarly journals Chloride and sodium influx: a coupled uptake mechanism in the squid giant axon.

1979 ◽  
Vol 73 (6) ◽  
pp. 801-818 ◽  
Author(s):  
J M Russell
Keyword(s):  
Giant Axon ◽  
Squid Giant Axon ◽  
Uptake Mechanism ◽  
External Concentration ◽  
Sodium Influx ◽  
Unidirectional Fluxes ◽  
Chloride Influx

The squid giant axon was internally dialyzed while the unidirectional fluxes of either Cl or Na were measured. The effects of varying the internal or external concentration of either Na or Cl were studied. Chloride influx was directly proportional to the external Na concentration whereas Cl efflux was unaffected by changes of the external Na concentration between 0 and 425 mM. Neither Cl influx nor efflux were affected by changes of internal Na concentration over the range of 8-158 mM. After ouabain and TTX treatment a portion of the remaining Na influx was directly dependent on the extracellular Cl concentration. Furthermore, when the internal Cl concentration was increased from 0 to 150 mM, the influxes of Cl and Na were decreased by 14 and 11 pmol/cm2.s, respectively. The influx of both ions could be substantially reduced when the axon was depleted of ATP. The influxes of both ions were inhibited by furosemide but unaffected by ouabain. It is concluded that the squid axolemma has an ATP-dependent coupled Na-Cl co-transport uptake mechanism.

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

Fractionation of the asymmetry current in the squid giant axon into inactivating and non-inactivating components

1982 ◽  
Vol 215 (1200) ◽  
pp. 375-389 ◽  
Keyword(s):  
Conformational Changes ◽  
Time Course ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Gating System ◽  
Nerve Membrane ◽  
Positive Voltage ◽  
The Asymmetry ◽  
Displacement Currents ◽  
Asymmetrical Displacement

The operation of the voltage-sensitive sodium gating system in the nerve membrane involves conformational changes that are accompanied by small asymmetrical displacement currents. The asymmetry current may be divided into a component that is inactivated by positive voltage-clamp pulses, and recovers from inactivation with exactly the same time course as the sodium conductance, and one that is not inactivated. A method is described for recording the two components separately with the aid of an inactivating prepulse. They appear to have a marked difference in their rising phases, that of the non-inactivating component being just about as fast as the imposed step in membrane potential, while the inactivating component requires some tens of microseconds to reach its peak.

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 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.

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