Abstract

BAY K 8644, a drug that elicits calcium-dependent muscle contraction, inhibits binding of the voltage-dependent calcium channel antagonist [ 3H]nitrendipine to brain and PC12 pheochromocytoma cell membranes. This effect is due to high-affinity ( K i = 4.5nM) competitive inhibition at the binding site for dihydropyridine calcium antagonists. Allosteric sites that mediate calcium channel blockade by non-dihydropyridine calcium antagonists are not similarly affected. Our findings indicate that BAY K 8644 is active at central, as well as peripheral, calcium channels and are compatible with a multi-state model of the voltage-dependent calcium channel in which antagonist drugs promote a closed state of the channel, while BAY K 8644 promotes an open state.

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