ω-Conotoxin GVIA blocks nicotine-induced catecholamine secretion by blocking the nicotinic receptor-activated inward currents in bovine chromaffin cells
ABSTRACT 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 ω-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 ω-conotoxin GVIA (1 μM). However, nicotine-induced both norepinephrine and epinephrine secretion were similarly blocked (about 25%) by ω-conotoxin GVIA (1 μM). 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, ω-conotoxin GVIA is a potent and reversible blocker of the nicotinic receptor-induced currents in chromaffin cells.