Pharmacological studies on supersensitization. VI. Effect of cocaine on the utilization of calcium in acetylcholine-induced contraction of isolated vas deferens of guinea pig.

Abstract

Effects of cocaine on the isotonic contractions of isolated intact and glycerinated vas deferens of guinea pig were examined. Cocaine potentiated the contractile responses of vas deferens to acetylcholine and potassium chloride in standard and calcium-free Tyrode solution. Cocaine also augmented the maximum response of calcium-induced contraction of partially depolarized vas deferens. The contractile responses to potassium chloride in standard Tyrode solution were completely abolished by lanthanum chloride, while the contractile responses to acetylcholine in standard Tyrode solution were attenuated by lanthanum chloride and the residual contractions were not affected by cocaine. The half-time of decrease in acetylcholine-induced contraction in calcium-free Tyrode solution was significantly different from that of potassium-induced contraction in calcium-free Tyrode solution. Cocaine did not affect the contractile response of the glycerinated muscle piece of vas deferens. These results suggest that cocaine facilitates the transmembrane influx of calcium from extracellular fluid and/or superficial calcium-binding sites without affecting the release of calcium from intracellular calcium-binding sites.