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The leak mode of type II Na(+)-P(i) cotransporters.
Channels ( IF 3.3 ) Pub Date : 2008-11-08 , DOI: 10.4161/chan.2.5.6900
Olga Andrini 1 , Chiara Ghezzi , Heini Murer , Ian C Forster
Affiliation  

Na(+)-coupled phosphate cotransporters of the SLC34 gene family catalyze the movement of inorganic phosphate (P(i)) across epithelia by using the free energy of the downhill electrochemical Na(+) gradient across the luminal membrane. Electrogenic (NaPi-IIa/b) and electroneutral (NaPi-IIc) isoforms prefer divalent P(i) and show strict Na(+):P(i) stoichiometries of 3:1 and 2:1, respectively. For electrogenic cotransport, one charge is translocated per transport cycle. When NaPi-IIa or NaPi-IIb are expressed in Xenopus oocytes, application of the P(i) transport inhibitor phosphonoformic acid (PFA) blocks a leak current that is not detectable in the electroneutral isoform. In this review, we present the experimental evidence that this transport-independent leak originates from a Na(+)-dependent uniport carrier mode intrinsic to NaPi-IIa/b isoforms. Our findings, based on the characteristics of the PFA-inhibitable leak measured from wild-type and mutant constructs, can be incorporated into an alternating access class model in which the leak and cotransport modes are mutually exclusive and share common kinetic partial reactions.

中文翻译:

II型Na(+)-P(i)共转运体的泄漏模式。

通过使用下腔电化学Na(+)梯度穿过腔膜的自由能,SLC34基因家族的Na(+)偶联的磷酸盐共转运蛋白催化无机磷酸盐(P(i))穿过上皮细胞的运动。电源(NaPi-IIa / b)和电子中性(NaPi-IIc)同工型更喜欢二价P(i),并且分别显示出严格的Na(+):P(i)化学计量比为3:1和2:1。对于电共运输,每个运输周期转移一个电荷。当非洲爪蟾卵母细胞中表达NaPi-IIa或NaPi-IIb时,P(i)转运抑制剂膦甲酸甲酸(PFA)的施加会阻止在电子中性同工型中无法检测到的泄漏电流。在这篇综述中,我们提供了实验证据,表明这种与运输无关的泄漏源于NaPi-IIa / b异构体固有的Na(+)依赖性单端口载体模式。
更新日期:2019-11-01
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