大鼠低亲和力钠依赖二羧酸转运蛋白对枸橼酸及草酸转运电生理特性的研究

目的 探讨大鼠低亲和力钠依赖二羧酸转运蛋白(SDCT1)对枸橼酸及草酸的转运特点。方法克隆出大鼠SDCT1全长cDNA基因。应用爪蟾卵母细胞异源性表达SDCT1，并使用双电极电压钳法记录通道电流。通过改变灌流液中枸橼酸、草酸的浓度，以及两种底物转运时钠离子的浓度及pH值，对其特性进行了研究。结果SDCT1对枸橼酸及草酸的转运均为底物浓度及钠离子依赖。pH值变化显著影响2者的转运。但低pH对草酸的转运影响要远大于枸橼酸。结论在临床实践中，虽然升高尿液pH值可以抑制枸橼酸的重吸收，发挥其抑制钙盐沉积的功能。但过度地碱化尿液也会使草酸的重吸收受到抑制，使草酸大量存留在尿中而导致结行。保持适当的尿酸碱度是必要的。

The transport properties of rat renal low affinity Na (+)/dicarboxylate cotransporter for citrate and oxalate under voltage-clamp conditions

Objective To investigate the ability of rat renal Na (+ )-dicarboxylate cotransporter(SDCT1) to transport citrate and oxalate. Methods The SDCT1 full length cDNA was cloned from rat kidney.SDCT1 was transcribed in vitro and expressed in Xenopus laevis oocytes. Inward current generated by substrate(citrate or oxalate)was characterized using two-electrode voltageclamp technique. Results Steady-state citrate or oxalate evoked inward currents in SDCT1 were dependent on the concentrations of substrates and sodium and on the membrane potential. pH could significantly affect the transport of citrate and oxalate, but low pH had more potent effect on oxalate transport than that on citrate.Conclusion Even increasing the pH of urine can inhibit citrate reabsorption and the citrate forms soluble complexes with calcium, but too high pH will inhibit oxalate reabsorption more than citrate. Too much oxalate will deposit in urine and form stone. Thus, keeping reasonable urinary pH is necessary.