Biphasic short-circuit current response to noradrenaline mediated by Ca2+ and cAMP in cultured rat epididymal epithelium.
A study was carried out to investigate the short-circuit current (Isc) response to noradrenaline (NA) and the signal transduction mechanisms involved in cultured rat cauda epididymal epithelium. In normal Krebs-Henseleit solution, NA (10 mumol.l-1) added basolaterally elicited a biphasic Isc response consisting of a transient spike followed by a second sustained response. The biphasic response was almost abolished by removing ambient Cl-. Preloading the tissues with a cell-permeant Ca2+ chelator, 1,2-bis(2-aminophenoxy) ethane-N,N,N',N',-tetraacetic acid acetoxymethyl ester (BAPTA/AM), or pretreating them with thapsigargin (Tg), a microsomal adenosine triphosphatase inhibitor abolished the initial spike in the Isc response to NA, but had little effect on the second component. Pretreating the tissues with a non-selective beta-antagonist, nadolol, reduced the second Isc response in a dose-dependent fashion but the initial spike was not affected. Microfluorimetric studies showed that NA (100 mumol.l-1) elicited single Ca2+ spikes in isolated epididymal cells, which could be abolished by prior treatment with Tg. Biochemical assays showed that NA (10 mumol.l-1) increased intracellular cyclic adenosine monophosphate concentration ([cAMP]i) and the response was abolished by prior treatment with nadolol (50 mumol.l-1). The results showed that NA elicited a biphasic Isc response mediated by a rise in intracellular Ca2+ concentration ([Ca2+]i) followed by a rise in [cAMP]i. The Ca(2+)-mediated Isc response had a faster onset and more transient action than the cAMP counterpart. It is suggested that NA released from noradrenergic nerve endings regulates transepithelial Cl- secretion in the epididymis thereby providing the specialized millieu vital for sperm storage and maturation.
Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Shatin, New Territories.
A Y
AY
Leung
P Y
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Wong
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000032:analysis / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004822:Epididymis / Q000737:chemistry / Q000166:cytology* / Q000502:physiology*; D004847:Epithelial Cells; D004848:Epithelium / Q000737:chemistry / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D013729:Terpenes; D004533:Egtazic Acid; D019284:Thapsigargin; D000242:Cyclic AMP; D000252:Calcium-Transporting ATPases; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; D009638:Norepinephrine