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.

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.

Kinetic analysis of the sodium gating current in the squid giant axon

1990 ◽  
Vol 240 (1299) ◽  
pp. 411-423 ◽  
Keyword(s):  
Giant Axon ◽  
Squid Giant Axon ◽  
Critical Study ◽  
Gating Current ◽  
Time Constants ◽  
Delayed Onset ◽  
Sodium System ◽  
Relaxation Time Constants ◽  
Fast Rise ◽  
Intermediate Rate

A critical study has been made of the characteristics of the kinetic components of the sodium gating current in the squid giant axon, of which not less than five can be resolved. In addition to the principal fast component I g 2 , there are two components of appreciable size that relax at an intermediate rate, I g 3a and I g 3b , I g 3a has a fast rise, and is present over the whole range of negative test potentials. I g 3b absent below -40 mV, exhibits a delayed onset and disappears on inactivation of the sodium system. There are also two smaller components, I g 1 and I g 4 , with very fast and much slower relaxation time constants, respectively.

The kinetics of voltage-gated ion channels

1994 ◽  
Vol 27 (4) ◽  
pp. 339-434 ◽  
Author(s):  
R. D. Keynes
Keyword(s):  
Ion Channels ◽  
Ionic Currents ◽  
Giant Axon ◽  
General Information ◽  
Squid Giant Axon ◽  
Voltage Gated ◽  
Voltage Gated Ion Channels ◽  
Kinetics Of ◽  
Electrical Data ◽  
Gated Ion Channels

When Hodgkin & Huxley (1952) first embarked on the analysis of their voltageclamp data on the ionic currents in the squid giant axon, they hoped to be able to deduce a mechanism from it, but it soon became clear that the electrical data would by themselves yield only very general information about the class of system likely to be involved.

Selective action of scorpion neurotoxins on the ionic currents of the squid giant axon

Toxicon ◽  
1983 ◽  
Vol 21 ◽  
pp. 57-60 ◽  
Author(s):  
Emilio Carbone ◽  
Prestipino Gianfranco ◽  
Enzo Wanke ◽  
Lourival D. Possani ◽  
Alfred Maelicke
Keyword(s):  
Ionic Currents ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Selective Action

scholarly journals Single channel studies of the phosphorylation of K+ channels in the squid giant axon. II. Nonstationary conditions.

1991 ◽  
Vol 98 (1) ◽  
pp. 19-34 ◽  
Author(s):  
E Perozo ◽  
D S Jong ◽  
F Bezanilla
Keyword(s):  
Voltage Dependence ◽  
Single Channel ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Delayed Rectifier ◽  
Activation Process ◽  
Inactivation Curve ◽  
Caged Atp ◽  
Delayed Rectifier Current ◽  
Voltage Curve

The effects of phosphorylation on the properties of the 20-pS channel of the squid giant axon were studied using the cut-open axon technique. Phosphorylation of the channel was achieved by photoreleasing caged ATP (inside the patch pipette) in the presence of the catalytic subunit of the protein kinase A. An inverted K+ gradient (500 K+ external parallel 5 K+ internal) was used to study the activation process. Phosphorylation decreased the frequency of openings of the channel at most potentials by shifting the probability vs. voltage curve toward more positive potentials. The mean open times showed no voltage dependence and were not affected by phosphorylation. The distribution of first latencies, on the other hand, displayed a sharp voltage dependence. Phosphorylation increased the latency to the first opening at all potentials, shifting the median first latency vs. voltage curve toward more positive potentials. The slow inactivation process was studied in the presence of a physiological K+ gradient (10 K+ external parallel 310 K+ internal). Pulses to 40 mV from different holding potentials were analyzed. Phosphorylation increases the overall ensemble probability by decreasing the number of blank traces. A single channel inactivation curve was constructed by computing the relative appearance of blank traces at different holding potentials before and after photoreleasing caged ATP. As determined in dialyzed axons, the effect of phosphorylation consisted in a shift of the inactivation curve toward more positive potentials. The 20-pS channel has the same characteristics as the delayed rectifier current in activation kinetics, steady-state inactivation, and phosphorylation effects.

Sign in / Sign up

Export Citation Format

Share Document