Effects of capsaicin on molluscan neurons: an intracellular study

Effects of capsaicin (CAP) on membrane properties and action potentials (AP) were studied (30-300 microM, at 22 degrees C, pH 7.4) in Helix and Aplysia neurons. CAP (100-300 microM) depolarized the cell membrane and increased the slope resistance. The neuronal firing increased and/or the spike threshold decreased. CAP differentially affected the APs generated in A- and B-cells in Helix or S- and F-cells in Aplysia. Plateau-like prolongation of the APs with a concomitant increase of the hump duration was observed in A-cells, while a significant prolongation of the spike duration was at 90% repolarization time in B-cells. The electrophysiological changes proved to be similar when CAP acted in homologous Helix and Aplysia neurons, but were less pronounced in the latter animal. CAP decreased the rate of rise and the rate of fall of the APs and shortened the action potential duration (APD) in Na-free (TEA) solution. CAP-induced events were dose-dependent and reversible.