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

Abstract

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 Na conductance indicates that activation of the Na system involves either 3 subunits operating in parallel or a 3-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 Na channels. Inactivation is coupled sequentially to activation. The evidence appears to argue against a trimeric system with 3 independent subunits and favors a monomeric system that undergoes a complex sequence of conformational changes.