Kinetics of sodium activation in giant axons of squid (Doryteuthis bleekeri)

The variation with time of the rising phase of the sodium conductance in squid giant axons was fitted to the Xth power of running integrals of the colchicine-sensitive components of the asymmetry currents, where the running integrals were experimentally obtained. We found that excellent fitting was obtained for all of the potentials examined from -60 to +60 mV, when we put the value of X equal to 3 at potentials above 10 mV and equal to 5 below -20 mV, and it varied continuously from 3 to 5 when pulse potentials changed from 10 to -25 mV. Further, it was found that the voltage dependence of the peak sodium currents was fitted to the third power of charges carried by the colchicine-sensitive component of the asymmetry current by the moment when the sodium current attained its peak. These results agree well with the expectation by Hodgkin and Huxley [(1952) J. Physiol., Lond. 117, 500-544] although the gating kinetics differ from the Hodgkin-Huxley prediction [Matsumoto, Ichikawa and Tasaki (1983) J. Membr. Biol. 77, 93-99].