title: Na+ reabsorption in cultured rat epididymal epithelium via the Na+/nucleoside cotransporter.
abstract: The effect of nucleoside on Na+ reabsorption via Na+/nucleoside cotransporter in cultured rat epididymal epithelia was studied by short-circuit current (Isc) technique. Guanosine added apically stimulated Isc in a dose-dependent manner, with a median effective concentration (EC50) of 7 +/- 2 microM (mean +/- SEM). Removal of Na+ from the apical bathing solution or pretreatment with a nonspecific Na+/nucleoside cotransporter inhibitor, phloridzin, completely blocked the Isc response to guanosine. Moreover, the guanosine response was abolished by pretreatment of the tissue with ouabain, a Na+/K+-ATPase inhibitor, suggesting the involvement of Na+/nucleoside cotransporter on the apical side and Na+/K+-ATPase on the basolateral side in Na+ reabsorption. In contrast, the Isc response to guanosine was not affected after desensitization of purinoceptors by ATP. Addition of the Na+/K+/2Cl- symport inhibitor bumetanide to the basolateral side or the nonspecific Cl- channel blocker diphenylamine-2-carboxylate to the apical side showed no effect on the Isc response to guanosine, excluding stimulation of Cl- secretion by guanosine as the cause of the guanosine-induced Isc. The Isc response to purine nucleoside (guanosine and inosine) was much higher than that to pyrimidine nucleoside (thymidine and cytidine). Consistent with substrate specificity, results of reverse transcription-polymerase chain reaction revealed mRNA for concentrative nucleoside transporter (CNT2), which is a purine nucleoside-selective Na+/nucleoside cotransporter in the epididymis, but not for CNT1. It is suggested that the Na+/nucleoside cotransporter (i.e., CNT2) may be one of the elements involved in Na+ and fluid reabsorption in the epididymis, thereby providing an optimal microenvironment for the maturation and storage of spermatozoa.
authors.affiliation: Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Shatin, N.T., Hong Kong.
authors.forename: G P
authors.initials: GP
authors.lastname: Leung
authors.forename: K H
authors.initials: KH
authors.lastname: Cheung
authors.forename: C M
authors.initials: CM
authors.lastname: Tse
authors.forename: P Y
authors.initials: PY
authors.lastname: Wong
mesh_terms: D000042:Absorption; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000502:physiology; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004822:Epididymis / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism; D015870:Gene Expression; D006151:Guanosine / Q000494:pharmacology*; D008297:Male; D026901:Membrane Transport Proteins; D018408:Patch-Clamp Techniques; D010695:Phlorhizin / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D013379:Substrate Specificity; D062367:ortho-Aminobenzoates / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D002352:Carrier Proteins; D018118:Chloride Channels; D026901:Membrane Transport Proteins; D012333:RNA, Messenger; C065171:cif nucleoside transporter; D062367:ortho-Aminobenzoates; D002034:Bumetanide; D006151:Guanosine; D000255:Adenosine Triphosphate; D004247:DNA; C001209:fenamic acid; D012964:Sodium; D010695:Phlorhizin; D000254:Sodium-Potassium-Exchanging ATPase