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Neuronal sodium and potassium channels: structure and function.

Information transfer over long distances within the central nervous system is achieved because neurones are capable of generating and conducting action potentials. Such action potentials are the all or none signals or messages of the nervous system and depend on the operation of specialized membrane proteins called ion channels. More than 50 years ago, Cole and Curtis [16] showed that the electrical conductance of the nerve axon membrane increased during the action potential, suggesting that the movement of ions was involved. In 1952, Hodgkin and Huxley published a classic series of papers [43] describing formally the ionic basis of the action potential in terms of sequential membrane permeability changes to Na and K ions. Now, 40 years on, we are on the threshold of describing the molecular basis of excitability [10, 14, 15, 27, 54]. Thus the Na and K channels have been elevated from the status of mythical structures in the minds of electrophysiologists to a position where they are in danger of being crystallized. The combination of traditional biophysical and biochemical methods with the powerful techniques of molecular biology has advanced work in this field to the point that the structure of membrane Na and K channels is within reach [14, 15]. This review is intended as an introduction to the properties of neuronal Na and K channels, with some reference to the effects of anaesthetics. It will serve as a background to the material presented in subsequent reviews.