title: Cl- transport via anion exchange in Necturus renal microvillus membranes.
abstract: We investigated the mechanism of Cl- transport in microvillus membrane vesicles isolated from Necturus kidneys. Cl- influx was insensitive to changes in membrane potential induced by K+ gradients and the K+ ionophore valinomycin, arguing against conductive Cl- transport. Inward gradients of Na+ or Na+ + K+ did not stimulate initial Cl- influx, arguing against direct Na+-Cl- or Na+-K+-Cl- cotransport. External Cl-, HCO3-, and NO3- each stimulated 36Cl efflux and inhibited 36Cl uptake, indicating anion exchange. Outward HCO3- gradients but not OH- gradients stimulated 36Cl influx, consistent with Cl- -HCO3- exchange. Cl- transport via anion exchange was inhibited by furosemide, bumetanide, and disulfonic stilbenes, but not by acetazolamide. External halides stimulated 36Cl efflux (Cl- = Br- greater than I- greater than F-) but the organic anions lactate, p-aminohippurate, and urate did not. Amiloride-sensitive Na+-H+ exchange was demonstrated. Finally, in the presence of a CO2/HCO3 buffer system, imposing an inward Na+ gradient caused a time-delayed stimulation of 36Cl uptake, consistent with indirect coupling of Na+-H+ and Cl- -HCO3- exchangers. We conclude that the parallel operation of Na+-H+ and Cl- -HCO3- exchangers rather than direct cotransport may account for the Na+-coupled uphill Cl- entry previously observed in the intact proximal tubular cell of Necturus.
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D000838:Anions / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism; D001692:Biological Transport; D002712:Chlorides / Q000378:metabolism*; D002713:Chlorine; D004058:Diffusion; D004594:Electrophysiology; D006859:Hydrogen / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism*; D009337:Necturus; D011188:Potassium / Q000378:metabolism; D011868:Radioisotopes; D012964:Sodium / Q000378:metabolism; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D000838:Anions; D001639:Bicarbonates; D002712:Chlorides; D011868:Radioisotopes; D014634:Valinomycin; D002713:Chlorine; D000584:Amiloride; D006859:Hydrogen; D012964:Sodium; D011188:Potassium