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.

Sodium gating currents in Myxicola giant axons

1976 ◽  
Vol 193 (1113) ◽  
pp. 469-475 ◽  
Keyword(s):  
Giant Axon ◽  
Gating Currents ◽  
Giant Axons ◽  
Displacement Currents ◽  
Asymmetrical Displacement

Asymmetrical displacement currents similar to those identified elsewhere as sodium gating currents have been recorded in the giant axon of Myxicola , and their characteristics are briefly described.

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

COMPONENTS OF THE ASYMMETRY CURRENT IN THE SQUID GIANT AXON

1981 ◽  
pp. 37-49
Author(s):  
R.D. Keynes ◽  
G.C. Malachowski ◽  
D.F. Van Helden ◽  
N.G. Greeff
Keyword(s):  
Giant Axon ◽  
Squid Giant Axon ◽  
The Asymmetry

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 Potassium conductance of the squid giant axon. Single-channel studies.

1988 ◽  
Vol 92 (2) ◽  
pp. 179-196 ◽  
Author(s):  
I Llano ◽  
C K Webb ◽  
F Bezanilla
Keyword(s):  
Time Course ◽  
Single Channel ◽  
Potassium Conductance ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
K Channel ◽  
Delayed Rectifier ◽  
Fluctuation Analysis ◽  
Patch Clamp Technique ◽  
Relative Contribution

The patch-clamp technique was implemented in the cut-open squid giant axon and used to record single K channels. We present evidence for the existence of three distinct types of channel activities. In patches that contained three to eight channels, ensemble fluctuation analysis was performed to obtain an estimate of 17.4 pS for the single-channel conductance. Averaged currents obtained from these multichannel patches had a time course of activation similar to that of macroscopic K currents recorded from perfused squid giant axons. In patches where single events could be recorded, it was possible to find channels with conductances of 10, 20, and 40 pS. The channel most frequently encountered was the 20-pS channel; for a pulse to 50 mV, this channel had a probability of being open of 0.9. In other single-channel patches, a channel with a conductance of 40 pS was present. The activity of this channel varied from patch to patch. In some patches, it showed a very low probability of being open (0.16 for a pulse to 50 mV) and had a pronounced lag in its activation time course. In other patches, the 40-pS channel had a much higher probability of being open (0.75 at a holding potential of 50 mV). The 40-pS channel was found to be quite selective for K over Na. In some experiments, the cut-open axon was exposed to a solution containing no K for several minutes. A channel with a conductance of 10 pS was more frequently observed after this treatment. Our study shows that the macroscopic K conductance is a composite of several K channel types, but the relative contribution of each type is not yet clear. The time course of activation of the 20-pS channel and the ability to render it refractory to activation only by holding the membrane potential at a positive potential for several seconds makes it likely that it is the predominant channel contributing to the delayed rectifier conductance.

The relationship between the inactivating fraction of the asymmetry current and gating of the sodium channel in the squid giant axon

1982 ◽  
Vol 215 (1200) ◽  
pp. 391-404 ◽  
Keyword(s):  
Conformational Changes ◽  
Voltage Dependence ◽  
Ionic Currents ◽  
Giant Axon ◽  
Quantitative Comparison ◽  
Squid Giant Axon ◽  
Relative Timing ◽  
Sodium System ◽  
Opening And Closing ◽  
The Relationship

A quantitative comparison between the voltage dependence of the inactivating component of the asymmetrical charge transfer in the squid giant axon and that of the sodium conductance indicates that activation of the sodium system involves either three subunits operating in parallel or a three-step series mechanism. This is confirmed by an examination of the relative timing of the flow of asymmetry and ionic currents during the opening and closing of the sodium channels. In agreement with previous suggestions, inactivation is coupled sequentially to activation. The evidence appears to argue against a trimeric system with three wholly independent subunits and favours a monomeric system that undergoes a complex sequence of conformational changes.

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 The effect of local anaesthetics on the components of the asymmetry current in the squid giant axon.

1984 ◽  
Vol 352 (1) ◽  
pp. 653-668 ◽  
Author(s):  
J M Bekkers ◽  
N G Greeff ◽  
R D Keynes ◽  
B Neumcke
Keyword(s):  
Giant Axon ◽  
Local Anaesthetics ◽  
Squid Giant Axon ◽  
The Asymmetry
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