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The Na-P cotransporter PiT-2 (SLC20A2) is expressed in the apical membrane of rat renal proximal tubules and regulated by dietary P

American Journal of Physiology - Renal Physiology, ISSN: 1522-1466, Vol: 296, Issue: 4, Page: F691-9
2009
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The principal mediators of renal phosphate (P) reabsorption are the SLC34 family proteins NaPi-IIa and NaPi-IIc, localized to the proximal tubule (PT) apical membrane. Their abundance is regulated by circulatory factors and dietary P. Although their physiological importance has been confirmed in knockout animal studies, significant P reabsorptive capacity remains, which suggests the involvement of other secondary-active P transporters along the nephron. Here we show that a member of the SLC20 gene family (PiT-2) is localized to the brush-border membrane (BBM) of the PT epithelia and that its abundance, confirmed by Western blot and immunohistochemistry of rat kidney slices, is regulated by dietary P . In rats treated chronically on a high-P (1.2%) diet, there was a marked decrease in the apparent abundance of PiT-2 protein in kidney slices compared with those from rats kept on a chronic low-P (0.1%) diet. In Western blots of BBM from rats that were switched from a chronic low- to high-P diet, NaPi-IIa showed rapid downregulation after 2 h; PiT-2 was also significantly downregulated at 24 h and NaPi-IIc after 48 h. For the converse dietary regime, NaPi-IIa showed adaptation within 8 h, whereas PiT-2 and NaPi-IIc showed a slower adaptive trend. Our findings suggest that PiT-2, until now considered as a ubiquitously expressed P housekeeping transporter, is a novel mediator of P reabsorption in the PT under conditions of acute P deprivation, but with a different adaptive time course from NaPi-IIa and NaPi-IIc. Copyright © 2009 the American Physiological Society.

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