Bibert Stéphanie, Hess Solange Kharoubi, Firsov Dmitri, Thorens Bernard, Geering Käthi, Horisberger Jean-Daniel, Bonny Olivier
Dept. of Pharmacology and Toxicology, Univ. of Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland.
Am J Physiol Renal Physiol. 2009 Sep;297(3):F612-9. doi: 10.1152/ajprenal.00139.2009. Epub 2009 Jul 8.
GLUT9 (SLC2A9) is a newly described urate transporter whose function, characteristics, and localization have just started to be elucidated. Some transport properties of human GLUT9 have been studied in the Xenopus laevis oocyte expression system, but the type of transport (uniport, coupled transport system, stoichiometry ... .) is still largely unknown. We used the same experimental system to characterize in more detail the transport properties of mouse GLUT9, its sensitivity to several uricosuric drugs, and the specificities of two splice variants, mGLUT9a and mGLUT9b. [(14)C]urate uptake measurements show that both splice variants are high-capacity urate transporters and have a K(m) of approximately 650 microM. The well-known uricosuric agents benzbromarone (500 microM) and losartan (1 mM) inhibit GLUT9-mediated urate uptake by 90 and 50%, respectively. Surprisingly, phloretin, a glucose-transporter blocker, inhibits [(14)C]urate uptake by approximately 50% at 1 mM. Electrophysiological measurements suggest that urate transport by mouse GLUT9 is electrogenic and voltage dependent, but independent of the Na(+) and Cl(-) transmembrane gradients. Taken together, our results suggest that GLUT9 works as a urate (anion) uniporter. Finally, we show by RT-PCR performed on RNA from mouse kidney microdissected tubules that GLUT9a is expressed at low levels in proximal tubules, while GLUT9b is specifically expressed in distal convoluted and connecting tubules. Expression of mouse GLUT9 in the kidney differs from that of human GLUT9, which could account for species differences in urate handling.
葡萄糖转运蛋白9（SLC2A9）是一种新发现的尿酸转运蛋白，其功能、特性和定位才刚刚开始得到阐明。人类葡萄糖转运蛋白9的一些转运特性已在非洲爪蟾卵母细胞表达系统中进行了研究，但转运类型（单向转运、偶联转运系统、化学计量……）仍大多未知。我们使用相同的实验系统更详细地描述了小鼠葡萄糖转运蛋白9的转运特性、其对几种促尿酸排泄药物的敏感性以及两种剪接变体mGLUT9a和mGLUT9b的特异性。[（14）C]尿酸摄取测量结果表明，两种剪接变体都是高容量尿酸转运蛋白，其米氏常数（K（m））约为650微摩尔。著名的促尿酸排泄剂苯溴马隆（500微摩尔）和氯沙坦（1毫摩尔）分别抑制葡萄糖转运蛋白9介导的尿酸摄取90%和50%。令人惊讶的是，葡萄糖转运蛋白阻滞剂根皮素在1毫摩尔时抑制[（14）C]尿酸摄取约50%。电生理测量表明，小鼠葡萄糖转运蛋白9介导的尿酸转运是生电性的且依赖电压，但与钠离子（Na（+））和氯离子（Cl（-））的跨膜梯度无关。综合来看，我们的结果表明葡萄糖转运蛋白9作为尿酸（阴离子）单向转运体发挥作用。最后，我们通过对从小鼠肾脏显微切割肾小管提取的RNA进行逆转录聚合酶链反应（RT-PCR）表明，mGLUT9a在近端小管中低水平表达，而mGLUT9b在远曲小管和连接小管中特异性表达。小鼠葡萄糖转运蛋白9在肾脏中的表达与人类葡萄糖转运蛋白9不同，这可能解释了尿酸处理的种属差异。
