DOI 10.1095/biolreprod.108.068346 Stimulating Effects of Dopamine on Chloride Transport Across the Rat Caudal

The present study investigated the effects of dopamine on chloride transport across cultured rat caudal epididymal epithelium. The results showed that dopamine induced a biphasic short-circuit current (Isc) in a concentration-dependent manner. The dopamine-induced response consisted of an initial rapid spike followed by a sustained phase. The alpha and beta adrenoreceptor inhibitors, phentolamine and propranolol, in-hibited the initial spike and the sustained phase, respectively, suggesting a contribution of adrenergic receptors. The response was almost abolished by removing the extracellular Cl, suggesting that the dopamine-induced short-circuit current is primarily a Cl current. The response was inhibited by the apical Cl channel blocker, diphenylamine-dicarboxylic acid, and the Ca2þ-activated Cl channel blocker, disulfonic acid stilbene, indicating that Cl may pass through two types of Cl channels on the apical side. Preloading monolayers with the intracellular Ca2þ chelator BAPTA/AM abolished the initial spike and greatly reduced the second phase in the Isc response to dopamine. Pretreating the monolayers with an adenylate cyclase inhibitor, MDL12330A, inhibited all of the second Isc response and part of the initial spike. Also, characteristics of the Cl currents induced by dopamine were observed in whole-cell patch-clamp record-ing. The increases of intracellular cAMP and Ca2þ induced by dopamine were also measured. The results suggest that extracellular dopamine activates Ca2þ-dependent and cAMP-dependent regulatory pathways, leading to activation of both Ca2þ-dependent and cAMP-dependent Cl conductances in epididymal epithelial cells. calcium, cyclic adenosine monophosphate, dopamine, epididymis, male reproductive trac