Inactivation of the Na permeability in squid giant axons

Inactivation of the Na permeability has been studied in intact and perfused squid giant axons with the voltage clamp method. The main results are: 1. Upon depolarization inactivation develops along an exponential time course; the upper limit for an initial delay in the development of inactivation is 50-100 musec. 2. Adding 20-40 mM KCl to K-free external solution accelerates the development of inactivation and slows its removal. 3. Scorpion venoms increase the maintained conductance, i.e. make inactivation less complete; the voltage dependence of the maintained conductance is different from that of the peak conductance.