Alkalosis-induced coronary vasoconstriction: effects of calcium, diltiazem, nitroglycerin, and propranolol.

We examined the effects of changes in pH, Ca2+ concentration, diltiazem, nitroglycerin, and propranolol on the vascular tone of the isolated rabbit coronary artery. Stepwise increase in pH of the bath fluid caused pH-dependent increased vascular tone. Increase in Ca2+ concentration of the bath fluid also resulted in increased vascular tone, while removal of Ca2+ abolished the high pH-induced elevated vascular tone. Diltiazem and nitroglycerin suppressed the high pH-induced increased vascular tone. Propranolol in high concentrations exhibited a direct inhibitory effect on the high pH-induced increased vascular tone. We conclude that high pH induces coronary vasoconstriction principally by increasing transmembrane influx of Ca2+ and that diltiazem and nitroglycerin suppress this action.