Effect of MCI-176, a new calcium antagonist, on the calcium induced contraction of isolated porcine coronary arteries.

Calcium antagonistic activity of MCI-176, a new calcium antagonist, was compared with those of diltiazem and nifedipine in isolated depolarized porcine coronary arteries. MCI-176, diltiazem and nifedipine competitively inhibited calcium contraction of the large coronary arteries, and their pA2 values were 7.49, 6.89 and 9.55, respectively. Similar competitive inhibition by MCI-176, diltiazem and nifedipine of calcium contraction was also observed in the small coronary arteries, and their pA2 values were 7.38, 6.83 and 9.91, respectively. Although calcium antagonistic activity of nifedipine was several hundreds times more potent than MCI-176 and diltiazem, the action of nifedipine, unlike MCI-176 and diltiazem, favored the small coronary arteries rather than the large coronary arteries.