Voltage Dependent Conductances: Gating Currents and Single Channel Recordings

Abstract

Since Hodgkin and Huxley published their famous series in 1952, we know that the generation and propagation of the nerve impulse, or action potential, is the result of transient permeability changes of the axon membrane to sodium and potassium. These authors studied the membrane currents of the squid axon as a function of membrane voltage using the “voltage clamp” technique. They found that the membrane permeability is voltage and time dependent and is the result of at least two different conduction systems for sodium and potassium (see Fig. 1). In this classical work, Hodgkin and Huxley introduced the concept of voltage dependent ionic conductances and they even separated the process of conduction from the process of opening and closing of the permeability pathway. Today the permeability pathway is called ionic channel of which a large number of different types have been identified and the primary structure has been determined for several of them (e.g. Noda et al., 1984).