Sequential Models of Sodium Channel Gating

Abstract

This chapter examines the advantages of state diagrams in the description of ionic-channel behavior and discusses the means available for determining the number of states and the rate constants of the transitions among them. Several means are available for determining the number of states and the rates of the transitions among them: (1) the measurement of macroscopic and single channel ionic currents and (2) the measurement of gating current. The four-state model is the simplest and is compatible with the macroscopic current kinetics in the squid giant axon. The mathematical description of the histograms that summarize single-channel kinetics is very similar to that for the time course of macroscopic current. With the exception of the closed time histogram, macroscopic currents and single-channel histograms give little information about the transition rates among closed states.In addition, gating current gives information about all steps in the activation sequence that involves charge movement.