OMEGA-CONOTOXIN GVIA BLOCKS NICOTINE-INDUCED CATECHOLAMINE SECRETION BY BLOCKING THE NICOTINIC RECEPTOR-ACTIVATED INWARD CURRENTS IN BOVINECHROMAFFIN CELLS

We have studied the contribution of N-type voltage-dependent Ca2+ chan nels to both norepinephrine and epinephrine secretion from bovine chro maffin cells induced by high K+ or nicotine using omega-conotoxin GVIA , a selective blocker of N-type voltage-dependent Ca2+ channels. We fo und that high K+ (75 mM) induced catecholamine secretion was not affec ted by exposure of bovine chromaffin cells to omega-conotoxin GVIA (1 mu M). However, nicotine-induced both norepinephrine and epinephrine s ecretion were similarly blocked (about 25%) by omega-conotoxin GVIA (1 mu M). This effect could be explained by a potent (about 80%) and rev ersible blockade of the inward current induced by nicotine receptor ac tivation in bovine chromaffin cells. The results indicate that besides the blockade of N-type voltage-dependent channels, omega-conotoxin GV IA is a potent and reversible blocker of the nicotinic receptor-induce d currents in chromaffin cells.