k CHANNEL AND CA CHANNEL CURRENTS AND THEIR INHIBITION BY GLIBENCLAMIDE IN SMOOTH MUSCLE CHLLS ISOLATED FROM GUINEA-PIG SEMINAL VESICLE

Smooth muscle cells of seminal vesicle exhibit excitatcry junction patential on nerve stimulation and can fire evoked) action potential (1). However) the type of ion channels that underlie this electrical activity have not been described. I have investigated the type and pharmacology of ion channel in freshly isolated smooth muscle cells from the guinea-pig seminal vesicle using whole-cell patch-clamp technique. Two types of outward) k-current, and one type of inward Ca-Current are characterised. The first outward current had a transient appearance and was clearly distinguishable from the Ca-sensitive sustained current. The outward currents were classified on the basis of their voltage- and Ca-dependent and their sensitivities to block by TEA and 3,4- diaminopyridine. The inward current was also voltage-dependent) showed slow inactivation and was abolished by Cd and inhibited by nifedipine. The action of glibenclamide was also investigated because this compound had a surprising relaxant effect on the seminal vesicle. Glibenclamide (500p..M) inhibited both the transient and sustained current indicating an IC50 of about 60p..M. These experiments suggest that at least three types of ion channel are present in seminal vesicle smooth muscle: A-Type K channel, Ca-activiated K channel and li-type Ca channel. The observed inhibitory effect of glibenclamide on Ca channel current may be a mechanism underlying its relaxant effect on the whole tissue.