Kuo S M, Aronson P S
Department of Medicine, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
J Biol Chem. 1996 Jun 28;271(26):15491-7. doi: 10.1074/jbc.271.26.15491.
Recent evidence suggests that apical membrane Cl--oxalate exchange plays a major role in mediating Cl- absorption in the renal proximal tubule. To sustain steady-state Cl- absorption by a mechanism of exchange for intracellular oxalate requires the presence of one or more pathways for recycling oxalate from lumen to cell. Accordingly, we evaluated the mechanisms of oxalate transport in luminal membrane vesicles isolated from the rabbit renal cortex. We found that transport of oxalate by Na+ cotransport is negligible compared to the transport of sulfate. In contrast, we demonstrated that oxalate shares the electroneutral pathway mediating Na+-independent sulfate-carbonate exchange. We also demonstrated the presence of OH--oxalate exchange (indistinguishable from H+-oxalate cotransport). The process of OH--oxalate exchange was electrogenic and partially inhibited by Cl-, indicating that it occurs, at least in part, as a mode of the Cl--oxalate exchanger described previously. An additional component of OH--oxalate exchange was insensitive to inhibition by either Cl- or sulfate, suggesting that it takes place by neither the Cl--oxalate exchanger nor the sulfate-carbonate exchanger. We conclude that multiple anion exchange mechanisms exist by which oxalate can recycle from lumen to cell to sustain Cl- absorption occurring via apical membrane Cl--oxalate exchange in the renal proximal tubule.
最近的证据表明，顶端膜氯离子-草酸盐交换在介导肾近端小管氯离子吸收中起主要作用。要通过与细胞内草酸盐交换的机制维持稳态氯离子吸收，需要存在一条或多条将草酸盐从管腔循环回细胞的途径。因此，我们评估了从兔肾皮质分离的管腔膜囊泡中草酸盐转运的机制。我们发现，与硫酸盐的转运相比，通过钠离子共转运的草酸盐转运可忽略不计。相反，我们证明草酸盐共享介导钠离子非依赖性硫酸盐-碳酸盐交换的电中性途径。我们还证明了氢氧根离子-草酸盐交换（与氢离子-草酸盐共转运无法区分）的存在。氢氧根离子-草酸盐交换过程是生电的，并受到氯离子的部分抑制，这表明它至少部分以先前描述的氯离子-草酸盐交换体的模式发生。氢氧根离子-草酸盐交换的另一个成分对氯离子或硫酸盐的抑制不敏感，这表明它既不是通过氯离子-草酸盐交换体也不是通过硫酸盐-碳酸盐交换体发生的。我们得出结论，存在多种阴离子交换机制，通过这些机制草酸盐可以从管腔循环回细胞，以维持通过肾近端小管顶端膜氯离子-草酸盐交换发生的氯离子吸收。
