Kinetic analysis of the sodium gating current in the squid giant axon

A critical study has been made of the characteristics of the kinetic components of the sodium gating current in the squid giant axon, of which not less than five can be resolved. In addition to the principal fast component I g 2 , there are two components of appreciable size that relax at an intermediate rate, I g 3a and I g 3b , I g 3a has a fast rise, and is present over the whole range of negative test potentials. I g 3b absent below -40 mV, exhibits a delayed onset and disappears on inactivation of the sodium system. There are also two smaller components, I g 1 and I g 4 , with very fast and much slower relaxation time constants, respectively.