Comparison of contractile effects of sodium vanadate and ouabain in vascular smooth muscles of guinea-pigs and rats.

Ouabain and vanadate are known as potent inhibitors of Na, K-ATPase in various tissues including smooth muscles. Both agents showed contractile action on various smooth muscles in a similar fashion: stronger contractile action on the aortae of rats (WKY and stroke prone spontaneously hypertensive rats, SHRSP) and guinea-pigs, and weaker contractile actions on basilar and mesenteric arteries of the same animals. Time to peak tension, however, was far longer in ouabain-induced contraction. Phentolamine depressed ouabain-induced contractions, while vanadate-induced contractions were not affected. Elevation of K+ concentration to 20 or 30 mM potentiated vanadate-induced contraction markely, while it potentiated ouabain-induced contraction only slightly. DIDS blocked vanadate-induced contraction but showed no effect on ouabain-induced contraction. Removal of Ca abolished ouabain-induced contractions, while vanadate-induced contractions of reduced height could be observed in the absence of Ca. Verapamil depressed both ouabain- and vanadate-induced contractions of WKY and SHRSP aorte aut exhibited no effect on the guinea-pig aorta. Thus, although similarities of the action of ouabain and sodium vanadate were observed, the modes of the actions were revealed to be different in the two agents. Inhibition of Na, K-ATPase might be involved in the case of ouabain-induced contractions, and inhibition of Ca-ATPase of membranous systems might be involved in vanadate-induced contraction.