A proposed membrane model for generation of sodium currents in squid giant axons.

An experimental review to show that axonal undercoat and cytoskeletal structures underneath the axolemma of squid giant axons play an important role in generating sodium currents is presented. Correspondingly, two alternative membrane models are proposed; one is that the undercoat and cytoskeletal structures support the functioning of sodium channels and the other is that they are directly incorporated with the molecular mechanism of generating sodium currents. This latter model is probable in squid giant axons. The model of direct participation of the underlying cytoskeleton in the sodium activation mechanism modifies the sodium activation gating kinetics in the Hodgkin-Huxley scheme; that is, the transition velocities between the open and closed states of the activation gate depend not only on membrane potentials but also on the time after the onset of application of a potential step.