Excitation of nerve or muscle requires an orderly opening and closing of molecular pores, the ionic channels, in the plasma membrane. During the action potential, Na channels are opened (activated) by the advancing wave of depolarisation, contributing a pulse of inward sodium current, and then are closed again (inactivated) by the continued depolarisation1. As one approach both to obtaining molecular information on the Na channel and towards further defining the recently discovered kinetic interactions of the inactivation and activation gating steps2-4, we have surveyed here the effects of chemical agents reported to slow or prevent Na channel inactivation. We find that many of the agents studied by others5-14 on invertebrate giant axons or vertebrate nerve act on our frog skeletal muscle preparation. In addition, we have discovered that simply lowering the intracellular pH nearly eliminates inactivation. The activation mechanism seems to resist modification.
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