Electrogenic cotransport of Na+ and sulfate in Xenopus oocytes expressing the cloned Na+SO4(2-) transport protein NaSi-1.
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.
Busch
A E
AE
Institute of Physiology I, Eberhard-Karls-Universität Tübingen, Germany.
Waldegger
S
S
Herzer
T
T
Biber
J
J
Markovich
D
D
Murer
H
H
Lang
F
F
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
D002352:Carrier Proteins; D027682:Cation Transport Proteins; D000077003:Sodium Sulfate Cotransporter; D013431:Sulfates; D027981:Symporters; D012964:Sodium