Binding properties of (+/-)[3H]benidipine hydrochloride to rat heart membranes

Benidipine is a newly developed slow-onset and long-lasting dihydropyridine calcium antagonist. The kinetics of specific binding of (+/-)[3H]benidipine to the dihydropyridine receptor sites in rat heart membranes were assessed. The dissociation constant (Kd) and the maximal number of binding sites were 0.078 +/- 0.029 nM and 286 +/- 6 fmol/mg of protein, respectively. Association and dissociation rate constants of (+/-)[3H]benidipine binding were 4 and 50 times smaller, respectively, than those of (+/-)[3H]nitrendipine binding. In displacement studies, the decreasing order of potency was benidipine, nisoldipine, nicardipine, nitrendipine, nifedipine, and Bay K 8644. A high stereoselectivity was observed, with Ki values of 0.028 nM in the S-S-(+) isomer and 4.4 nM in the R-R-(-) isomer of this drug. Benidipine had a high affinity for specific binding, with an inhibition constant of 0.084 nM, which was in good agreement with the Kd value stated above. Among the stimulants and blockers of alpha- and beta-adrenergic, cholinergic, histaminergic, dopaminergic, serotonergic, or GABAergic receptors, no drug inhibited or enhanced specific (+/-)[3H]benidipine binding. These binding properties of (+/-)[3H]benidipine may explain its unique slow onset and long-lasting antihypertensive activities.