Hyperpolarization and relaxation of canine vascular smooth muscle to vasoactive intestinal polypeptide

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