Gating Mechanism for the Activation of the Sodium Conductance in Nerve Membranes

Nerve fibers examined under voltage-clamp condi-tions show that after a sudden decrease in membrane potential, there are two independent kinetic compo-nents in the currents (Hodgkin and Huxley 1952a,b,c,d; Frankenhaeuser 1960, 1963; Armstrong et al. 1973). Each component represents an ionic flux and each pathway has a different selectivity (Chandler and Meves 1965; Rojas and Atwater 1967; Hille 1970; Rojas 1967a,b). In the giant axon of squid, the instan-taneous currents through each pathway are propor-tional to the membrane potential and are charac-terized by driving forces appropriate to ions moving passively down an electrochemical gradient (Hodgkin and Huxley 1952c,d; Bezanilla et al. 1970). The ionic conductances are activated by voltage, and the depend