EFFECT OF QUATERNARY AMMONIUM IONS ON ELECTRICAL ACTIVITY OF SPINAL GANGLION CELLS IN FROGS

Abstract

Quaternary ammonium ions such as choline, tetra-methylammonium, and tetraethylammonium markedly affect the electrical activity of nerve cell-bodies in the frog''s isolated spinal ganglion. Partial or total isosmotic replacement by these ions of the Na in the external medium prolongs (up to several seconds) action potentials, evoked and recorded through a single intracellular micro-electrode , without appreciably modifying the resting potential. Na depletion in the medium enhances the potency of these compounds. Membrane resistance is reduced during the whole course of prolonged potentials, but sometimes increases at the falling phase of less prolonged potentials. Intracellular injection of tetraethylammonium also prolongs action potentials, and restores excitability of cells blocked in Na-free sucrose media. These results suggest that quaternary ammonium ions do not substitute for external Na as charge carriers across the active membrane. The compounds can probably penetrate the resting membrane of cell-bodies and exert a specific action inside the membrane or in the perikaryon. Some possible explanations for the mechanism of electrical activity in Na-free media are discussed.