title: Independent Na+ and Cl- active transport by urinary bladder epithelium of brook trout.
abstract: Brook trout (Salvelinus fontinalis) urinary bladder in vitro had a low serosa-positive transepithelial potential (6.7 +/- 1.2 mV), low transmural conductance (0.23 +/- 0.03 mS. cm-2), and net absorptive transport of Na+ and Cl-. The net flux of Na+ was equivalent to that of Cl- and much larger than the membrane current, indicating neutral NaCl uptake. Na+ uptake was not coupled to that of Cl-, since absorptive Na+ transport continued in (Cl-)-free media. In the absence of Cl-, the net absorption of Na+ was accompanied by net secretion of titratable acidity, suggestive of Na+-H+ exchange on the luminal surface. Active Cl- transport persisted in dilute (2.0 mM) tetraethylammonium chloride with zero K+ and zero Na+, indicating full independence of the Cl- transport from cation coupling and suggesting the presence of Cl(-)-HCO-3 exchange. The kinetics of Cl- uptake (K1/2 = 35-37 mM, maximal transport rate = 3.0-3.4 mu eq . cm-2 . h-1) were not significantly affected by removal of mucosal Na+ . Cl- uptake was inhibited partially by 10(-4) M amiloride but not by 10(-4) M bumetanide. The results strongly support a model for active NaCl transport involving paired ion exchangers, likely located at the luminal membrane.
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active; D002034:Bumetanide / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D004553:Electric Conductivity; D004848:Epithelium / Q000378:metabolism; D005665:Furosemide / Q000494:pharmacology; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D014337:Trout; D001743:Urinary Bladder / Q000378:metabolism*
chemical_list: D002712:Chlorides; D002034:Bumetanide; D000584:Amiloride; D005665:Furosemide; D012964:Sodium; D011188:Potassium