Gating current "fractionation" in crayfish giant axons.

Effects of changes in initial conditions on the magnitude and kinetics of gating current and sodium current were studied in voltage-clamped, internally-perfused, crayfish giant axons. We examined the effects of changes in holding potential, inactivating prepulses, and recovery from inactivation in axons with intact fast inactivation. We also studied the effects of brief interpulse intervals in axons pretreated with chloramine-T for removal of fast inactivation. We find marked effects of gating current kinetics induced by both prepulse inactivation and brief interpulse intervals. The apparent changes in gating current relaxation rates cannot be explained simply by changes in gating charge magnitude (charge immobilization) combined with "Cole-Moore-type" time shifts. Rather they appear to indicate selective suppression of kinetically-identifiable components within the control gating currents. Our results provide additional support for a model involving parallel, nonidentical, gating particles.