Decreased density of binding sites for the Ca2+ channel antagonist [3H]isradipine after denervation of rat vas deferens.

Radioligand binding assays were performed with the selective antagonist of dihydropyridine-sensitive Ca2+ channels [3H]PN200-110 (isradipine) in rat vas deferens, before and 7 days after denervation, and data were compared with those obtained for K(+)-induced contractions, which are Ca(2+)-dependent. The density (Bmax) of dihydropyridine binding sites was decreased to almost one-third of its normal value after denervation. The respective affinity (KD) was not significantly changed. In addition, it was observed that the K(+)-induced tonic contraction, which corresponded to 55 +/- 2% of the respective phasic contraction, was decreased to 41 +/- 3% after denervation. It is assumed that the decreased density of Ca2+ channels causes a decrease in K(+)-induced influx of Ca2+ and consequently of the corresponding tonic contraction. These results indicate that autonomic innervation can regulate the density of dihydropyridine-sensitive Ca2+ channels in the rat vas deferens.