High affinity binding sites for [3H]-nitrendipine in rabbit uterine smooth muscle

The binding properties of the high affinity binding site for [3H]-nitrendipine on rabbit uteri membranes were investigated. The specific component had a dissociation constant of 0.46 +/- .07 nM and a maximal binding of 175 +/- 11 pmol/mg. A variety of other calcium channel blockers inhibited the binding of [3H]nitrendipine with varying potencies. Flunarizine demonstrated a high potency (IC50 = 0.30 microM) in inhibiting binding while verapamil and bepridil were less potent with IC50's of approximately 0.6-1.5 microM. Diltiazem did not displace nitrendipine even at very high concentrations. Verapamil displayed negative cooperative inhibition suggesting that a second site exists on uterine membranes for the binding of other calcium channel blockers.