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

Abstract

Radioligand binding assays were performed with the selective antagonist of dihydropyridine-sensitive Ca2+ channels [H-3]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 Ca2+-dependent. the density (B-max) of dihydropyridine binding sites was decreased to almost one-third of its normal value after denervation. the respective affinity (K-D) 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.