Calcium antagonistic action involved in vasodilation by brovincamine

Possible mode of vasodilative action of brovincamine was assessed in isolated cardiovascular preparations in comparison with verapamil and papaverine. Brovincamine (IC50: 1.2 x 10(-5) M), verapamil (IC50: 3.5 x 10(-7) M) or papaverine (IC50: 2.5 x 10(-5) M) caused a dose-dependent relaxation of potassium (30 mM)-contracture in the rabbit pulmonary arterial segment. This relaxation by verapamil or brovincamine, but not by papaverine, was antagonized by increasing external Ca2+ concentration to 12.4mM. Duration of slow action potentials of partially depolarized guinea-pig papillary muscle was reduced by 14 min exposure to brovincamine (5 x 10(-5) M) or verapamil (10(-5) M. These results suggest that brovincamine produces a vasodilation via a slow Ca2+-channel blockade.