title: Different regulatory pathways involved in ATP-stimulated chloride secretion in rat epididymal epithelium.
abstract: The regulatory pathways involved in the ATP-stimulated Cl- secretion across rat epididymal epithelium were investigated by the short-circuit current (ISC) technique. Biphasic characteristic was observed in the ISC responded to ATP (0.01-10 microM). Inhibitor of P1 receptor, 8-phenyltheophylline (up to 100 microM), did not have any effect on both phases of the ATP-stimulated ISC. The order of potency for stimulation of the two phases in ISC was ATP > ADP >> AMP, adenosine, consistent with the presence of P2-purinoceptors. Cl- channel blocker, disulfonic acid stilbene (DIDS, 300 microM), only inhibited the first peak of the ATP-stimulated ISC while diphenylamine-dicarboxylic acid (DPC, 1 mM) reduced both, indicating the involvement of different conductance pathways. DIDS was found to have an inhibitory effect on Ca(2+)-activated ISC (induced by ionomycin, 10 microM) but not cAMP-activated ISC (induced by forskolin, 1 microM) which could only be blocked by DPC. Both peaks of the ATP-activated ISC could be significantly inhibited by pretreatment with a Ca(2+)-chelating agent, BAPTA-AM (50 microM). An increase in cellular cAMP content upon stimulation of ATP was measured by radioimmunoassay. No significant increase in cAMP production was observed in cells stimulated with adenosine. The ATP-induced cAMP increase was prevented by pretreatment with BAPTA-AM (100 microM) indicating that cAMP production upon ATP stimulation was secondary to an increase in intracellular Ca2+ concentration. These results indicate that the ATP-stimulated Cl- secretion could be mediated by Ca2+ and cAMP-dependent regulatory pathways giving rise to the biphasic nature of the ATP-induced ISC.
authors.affiliation: Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Shatin.
authors.forename: H C
authors.initials: HC
authors.lastname: Chan
authors.forename: W L
authors.initials: WL
authors.lastname: Zhou
authors.forename: W O
authors.initials: WO
authors.lastname: Fu
authors.forename: W H
authors.initials: WH
authors.lastname: Ko
authors.forename: P Y
authors.initials: PY
authors.lastname: Wong
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D018118:Chloride Channels / Q000037:antagonists & inhibitors; D002712:Chlorides / Q000378:metabolism* / Q000502:physiology; D046508:Culture Techniques; D000242:Cyclic AMP / Q000502:physiology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004553:Electric Conductivity; D004822:Epididymis / Q000378:metabolism* / Q000502:physiology; D004848:Epithelium / Q000378:metabolism / Q000502:physiology; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D011983:Receptors, Purinergic / Q000502:physiology; D062367:ortho-Aminobenzoates / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D018118:Chloride Channels; D002712:Chlorides; D011983:Receptors, Purinergic; D062367:ortho-Aminobenzoates; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; C001209:fenamic acid; D000242:Cyclic AMP; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium