title: Sulfate transport by flounder renal tubule brush border: presence of anion exchange.
abstract: Transport of sulfate into brush border membrane (BBM) vesicles from renal tubules of southern flounder, Paralichthys lethostigma, was investigated. Imposition of a 21 mM HCO-3 gradient, in greater than out, produced concentrative sulfate uptake (overshoot) fourfold higher than equilibrium. Gradient conditions were necessary to produce this response; no overshoot was produced by the mere presence of HCO-3. Generation of potassium diffusion potentials with KCl gradients and valinomycin or short-circuiting of possible other ionic diffusion potentials had no effect on sulfate uptake. The rate-limiting step in HCO-3:SO2-4 exchange is, therefore, an electroneutral process. Although HCO-3 was the most effective counterion for sulfate, SCN-, Cl-, and S2O2-3 were also capable of promoting concentrative sulfate uptake. Sulfate uptake in the absence of counterion and bicarbonate-dependent sulfate uptake were both shown to be saturable processes. HCO-3-driven sulfate uptake could be inhibited by disulfonic stilbene, HgCl2, probenecid, chlorophenol red, and bromcresol green. Phloridzin, p-aminohippuric acid, 2,4-dinitrophenol, isethionic acid, and citric acid had no significant effect on HCO-3:SO2-4 exchange. The role of this sulfate:anion exchanger in active renal tubule sulfate secretion is discussed.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D017301:Ca(2+) Mg(2+)-ATPase; D002462:Cell Membrane / Q000378:metabolism*; D005399:Fishes; D007684:Kidney Tubules / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism*; D008954:Models, Biological; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013464:Sulfuric Acids / Q000378:metabolism*
chemical_list: D013464:Sulfuric Acids; D000469:Alkaline Phosphatase; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D000254:Sodium-Potassium-Exchanging ATPase