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Permanent URL to this publication: http://dx.doi.org/10.5167/uzh-1318

Forster, I C; Biber, J; Murer, H (2000). Proton-sensitive transitions of renal type II Na(+)-coupled phosphate cotransporter kinetics. Biophysical Journal, 79(1):215-230.

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Abstract

In the kidney proximal tubule, acidification of the glomerular filtrate leads to an inhibition of inorganic phosphate (P(i)) reabsorption by type II Na(+)-coupled cotransporters (NaPi-II). As external pH also alters the divalent/monovalent P(i) ratio, it has been difficult to separate putative proton interactions with the cotransporter from direct titration of divalent P(i), the preferred species transported. To distinguish between these possibilities and identify pH-sensitive transitions in the cotransport cycle, the pH-dependent kinetics of two NaPi-II isoforms, expressed in Xenopus laevis oocytes, were investigated electrophysiologically. At -50 mV, both isoforms showed >70% suppression of electrogenic response for an external pH change from 8.0 to 6.2, not attributable to titration of divalent P(i). This was accompanied by a progressive removal of steady-state voltage dependence. The NaPi-II-related uncoupled slippage current was unaffected by a pH change from 7.4 to 6.2, with no shift in the reversal potential, which suggested that protons do not function as substrate. The voltage-dependence of pre-steady-state relaxations was shifted to depolarizing potentials in 100 mM and 0 mM Na(ext)(+) and two kinetic components were resolved, the slower of which was pH-dependent. The changes in kinetics are predicted by a model in which protons interact with the empty carrier and final Na(+) binding step.

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Additional indexing

Item Type:Journal Article, refereed
Communities & Collections:04 Faculty of Medicine > Institute of Physiology
07 Faculty of Science > Institute of Physiology
DDC:570 Life sciences; biology
Language:English
Date:1 July 2000
Deposited On:11 Feb 2008 12:22
Last Modified:27 Nov 2013 16:22
Publisher:Elsevier
ISSN:0006-3495
Publisher DOI:10.1016/S0006-3495(00)76285-0
Related URLs:http://www.biophysj.org/cgi/content/full/79/1/215
PubMed ID:10866949

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