Membrane hyperpolarization and relaxation of canine blood vessels to vasoactive intestinal polypeptide

Abstract

The present study was designed to determine the influence of the vascular endothelium on membrane hyperpolarization induced by vasoactive intestinal polypeptide (VIP) in smooth muscle cells of canine isolated blood vessels, and the potential contribution that these electrophysiological changes may make to the relaxant effects of VIP. Membrane potential was measured in isolated canine coronary arteries and saphenous veins, using glass microelectrodes, and isometric force was recorded in a conventional organ chamber apparatus. All experiments were performed in the presence of indomethacin and nitro-L-arginine. VIP (10-9 M - 10-7 M) induced concentration-dependent and endothelium-independent hyperpolarization of the saphenous vein. This response was abolished by glibenclamide (10-6 M). VIP did not induce hyperpolarization of the coronary arterial preparations either in the presence or absence of the endothelium. VIP caused concentration-dependent and endothelium-independent relaxations of rings of both canine arterial and venous preparations. The relaxation of the saphenous vein to VIP was not influenced by glibenclamide (10-6 M). These data suggest that hyperpolarization of the cell membrane does not play a significant role in the relaxation of canine blood vessels induced by VIP.