title: Electrogenic cotransport of Na+ and sulfate in Xenopus oocytes expressing the cloned Na+SO4(2-) transport protein NaSi-1.
abstract: The Na+/sulfate cotransporter cloned from rat kidney cortex (NaSi-1) has been expressed in oocytes of Xenopus laevis and subjected to electrophysiological analysis by current and voltage clamp methods. In current-clamped oocytes, superfusion with 1 mM sulfate resulted in a 12-mV depolarization of the cell membrane. Accordingly, in voltage-clamped oocytes sulfate induced an inward current IS, which was dependent on both the concentration of Na+ and sulfate in the superfusate. Half-maximal IS was observed at about 0.1 mM sulfate and 70 mM Na+. The Hill coefficients were 1 and 2.8 for sulfate and Na+, respectively. Thiosulfate and selenate created similar currents as sulfate with a similar Km. At saturating concentrations of thiosulfate and selenate, addition of sulfate could not induce an additive current. Phosphate (1 mM) did not inhibit sulfate-induced currents. Finally, IS was dependent on the holding potential being larger at more negative potentials. The results of this study strongly suggest an electrogenic cotransport of sulfate and Na+ with a stoichiometry of 1:3.
authors.affiliation: Institute of Physiology I, Eberhard-Karls-Universität Tübingen, Germany.
authors.forename: A E
authors.initials: AE
authors.lastname: Busch
authors.forename: S
authors.initials: S
authors.lastname: Waldegger
authors.forename: T
authors.initials: T
authors.lastname: Herzer
authors.forename: J
authors.initials: J
authors.lastname: Biber
authors.forename: D
authors.initials: D
authors.lastname: Markovich
authors.forename: H
authors.initials: H
authors.lastname: Murer
authors.forename: F
authors.initials: F
authors.lastname: Lang
mesh_terms: D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D003001:Cloning, Molecular; D007672:Kidney Cortex / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008564:Membrane Potentials; D009865:Oocytes; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D000077003:Sodium Sulfate Cotransporter; D013431:Sulfates / Q000378:metabolism*; D027981:Symporters; D014982:Xenopus laevis
chemical_list: D002352:Carrier Proteins; D027682:Cation Transport Proteins; D000077003:Sodium Sulfate Cotransporter; D013431:Sulfates; D027981:Symporters; D012964:Sodium