Characterization of a Sodium-Dependent Concentrative Nucleobase-Transport System in Guinea-Pig Kidney Cortex Brush-Border Membrane-Vesicles

Griffith, Douglas A. and Jarvis, Simon M. (1994) Characterization of a Sodium-Dependent Concentrative Nucleobase-Transport System in Guinea-Pig Kidney Cortex Brush-Border Membrane-Vesicles. Biochemical Journal, 303 . pp. 901-905. ISSN 0264-6021. (The full text of this publication is not available from this repository)

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Abstract

The characteristics of hypoxanthine transport were examined in purified brush-border membrane Vesicles isolated from guineapig kidney. Hypoxanthine uptake in the vesicles was specifically stimulated by both Na+ and an inside-negative potential, resulting in a transient accumulation of intravesicular hypoxanthine. Nat-dependent hypoxanthine influx was saturable (apparent K-m 4.4 +/- 2.1 mu M, V-max. 128 +/- 29 pmol/min per mg of protein at 100 mM NaCl and 22 degrees C). Guanine, thymine, 5-fluorouracil and uracil inhibited hypoxanthine uptake (k(i) values 1-30 mu M), but adenine and the nucleosides inosine and thymidine were without effect. Guanine competitively inhibited Na+-dependent hypoxanthine influx, suggesting that it was a substrate for the active nucleobase transporter in guinea-pig renal membrane vesicles. A sigmoidal dependence between hypoxanthine influx and Na+ concentration was obtained (K-Na 13 +/- 2 mM; Hill coefficient, h, 2.13 +/- 0.14), suggesting that at least two Na+ ions are transported per hypoxanthine molecule. This system differs from the Na+-nucleobase carrier in cultured LLC-PK1 renal cells, which has a stoichiometric coupling ratio of 1:1. These results represent the first demonstration of an active electrogenic nucleobase carrier in renal apical membrane vesicles.

Item Type: Article
Subjects: Q Science > QP Physiology (Living systems) > QP517 Biochemistry
Divisions: Faculties > Science Technology and Medical Studies > School of Biosciences
Depositing User: P. Ogbuji
Date Deposited: 26 Jun 2009 08:58
Last Modified: 20 Jun 2014 14:01
Resource URI: http://kar.kent.ac.uk/id/eprint/20231 (The current URI for this page, for reference purposes)
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