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

We have studied the contribution of N-type voltage-dependent Ca2+ channels to both norepinephrine and epinephrine secretion from bovine chromaffin cells induced by high K+ or nicotine using omega-conotoxin GVIA, a selective blocker of N-type voltage-dependent Ca2+ channels. We found that high K+ (75 mM) induced catecholamine secretion was not affected by exposure of bovine chromaffin cells to omega-conotoxin GVIA (1 mu M). However, nicotine-induced both norepinephrine and epinephrine secretion were similarly blocked (about 25%) by omega-conotoxin GVIA (1 mu M). This effect could be explained by a potent (about 80%) and reversible blockade of the inward current induced by nicotine receptor activation in bovine chromaffin cells. The results indicate that besides the blockade of N-type voltage-dependent channels, omega-conotoxin GVIA is a potent and reversible blocker of the nicotinic receptor-induced currents in chromaffin cells.