Subject(s)
Receptors, Adrenergic, alpha/metabolism , Vas Deferens/metabolism , Adrenergic alpha-Agonists/pharmacology , Animals , Binding, Competitive , Calcium Channel Blockers/pharmacology , Male , Muscle Contraction/drug effects , Nifedipine/pharmacology , Norepinephrine/pharmacology , Rats , Vas Deferens/drug effects , Verapamil/pharmacologyABSTRACT
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.
