Functional characterization of acetylcholine receptors and calcium signaling in rat testicular capsule contraction

Abstract

The motor activity of mammalian testicular capsule (TC) contributes to male fertility and infertility, but the acetylcholine receptors related to the contractions induced by cholinergic drugs are poorly known. Indeed to characterize the acetylcholine receptors and cellular signaling by Ca2+ involved in TC motor activity of rats, the potency of agonists (pD(2)) and antagonists (pA(2)) of acetylcholine receptors, and effects of Ca2+ cellular transport blockers on the cholinergic contractions were evaluated pD(2) values of acetylcholine (5.98) were ten fold higher than that of carbachol (4.99). Efficacy (E-max) of acetylcholine and carbachol to induce contractions corresponded to 95% and 97% of E-max for KCl, but E-max for nicotine was very low (8% of E-max for KCl). Further, physostigmine did not affect the acetylcholine potency. Contractions induced by acetylcholine or carbachol were antagonized by muscarinic but not nicotinic antagonist. the order of pA(2) values obtained for muscarinic antagonists, namely atropine > 4-DAM-P > AF-DX116 > pirenzepine, corresponded to a typical profile of M-3 receptors. Contractions induced by acetylcholine or carbachol were inhibited by blockers of Ca2+ influx through voltage dependent calcium channels (nifedipine and Ni2+), Ca2+ reuptake by sarco-endoplasmic reticulum (cyclopiazonic acid) and mitochondria (FCCP). the protein kinase C (PKC) inhibitor chelerythrine only affected the acetylcholine induced contraction. These results suggest that TC motor activity of rats are mediated mainly by M-3 receptors followed by the increase of cytosolic Ca2+ concentration regulated by voltage dependent calcium channels, sarco-endoplasmic reticulum and mitochondria. Furthermore, the differential effects of chelerythrine in the acetylcholine or carbachol-induced contractions are discussed. (C) 2013 Elsevier B.V. All rights reserved.