Orthovanadate inhibits adrenaline-induced hyperpolarization in amphibian sympathetic ganglia

The adrenaline-induced hyperpolarization of neurones in sympathetic ganglia of Rana pipiens was recorded by means of the sucrose gap technique. This hyperpolarization was inhibited in a concentration-dependent manner by sodium orthovanadate (0.1-1.0 mM). Although orthovanadate inhibited the hydrolysis of ATP by preparations of microsomal Na+/K+ ATPase from frog nerve (IC50 = 3.0 microM), extracellularly-applied orthovanadate did not inhibit electrogenic sodium pumping in intact sympathetic ganglia of Rana pipiens. This and other observations that extracellularly-applied orthovanadate did not enter sympathetic neurones and did not have access to intracellular enzyme systems. It is suggested that orthovanadate acts at an extracellular site to inhibit the adrenaline-induced hyperpolarization.