Busch A E, Waldegger S, Herzer T, Biber J, Markovich D, Murer H, Lang F
Institute of Physiology I, Eberhard-Karls-Universität Tübingen, Germany.
J Biol Chem. 1994 Apr 29;269(17):12407-9.
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.
从大鼠肾皮质克隆的钠/硫酸盐共转运体（NaSi-1）已在非洲爪蟾卵母细胞中表达，并通过电流钳和电压钳方法进行电生理分析。在电流钳制的卵母细胞中，用1 mM硫酸盐灌注导致细胞膜去极化12 mV。相应地，在电压钳制的卵母细胞中，硫酸盐诱导内向电流IS，其依赖于灌流液中Na+和硫酸盐的浓度。在约0.1 mM硫酸盐和70 mM Na+时观察到半数最大IS。硫酸盐和Na+的希尔系数分别为1和2.8。硫代硫酸盐和硒酸盐产生与硫酸盐相似的电流，Km相似。在硫代硫酸盐和硒酸盐的饱和浓度下，添加硫酸盐不能诱导叠加电流。磷酸盐（1 mM）不抑制硫酸盐诱导的电流。最后，IS依赖于钳制电位，在更负的电位下更大。本研究结果强烈提示硫酸盐和Na+以1:3的化学计量比进行电生性共转运。
