CHARACTERIZATION OF 1,4DIHYDROPYRIDINE CALCIUM-CHANNEL BINDING-SITES IN THE HUMAN PROSTATE

The binding and functional properties of calcium channel receptors have not been previously characterized in the normal or hyperplastic prostate. Dihydropyridine (DHP) binding sites have been characterized in other tissues using the ligands 3H-nitrendipine and (+)3H-PN200-110. Saturation experiments were performed on homogenates obtained from five human prostate adenomas using these ligands. The binding of 3H-nitrendipine and (+)3H-PN200-110 in the prostate was saturable and of high affinity. The mean K(d) of 3H-nitrendipine and (+)3H-PN200-110 was 0.92 ± 0.11 nM and 0.14 ± 0.02 nM, respectively. The mean B(max) of 3H-nitrendipine and (+)3H-PN200-110 was 0.57 ± 0.06 and 0.19 ± 0.02 fmol/mg. wet wt., respectively. The percent specific binding of 3H-nitrendipine and (+)3H-PN200-110 was 18 ± 1% and 38 ± 4%, respectively. The pharmacology of (+)3H-PN200-110 binding sites was further characterized using competition displacement experiments. The IC50 corrected values for Bay K 8644, nifedipine, verapamil, and diltiazem in the human prostate and other tissues are of the same order of magnitude. The prostate contains an abundance of high affinity DHP binding sites. The physiologic significance of the DHP binding sites in the prostate requires further investigation.