Mechanisms of trans-chloride activation of a Cl−/H+ symport in brush-border membrane vesicles from guinea-pig ileum

1989 ◽  
Vol 17 (6) ◽  
pp. 1004-1004 ◽  
Author(s):  
MONIQUE VASSEUR ◽  
MICHELE CAÜZAC ◽  
KHADIJA TOUZANI ◽  
FRANCISCO ALVARADO
Keyword(s):  
Guinea Pig ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Guinea Pig Ileum

scholarly journals Characterization of a sodium-dependent concentrative nucleobase-transport system in guinea-pig kidney cortex brush-border membrane vesicles

1994 ◽  
Vol 303 (3) ◽  
pp. 901-905 ◽  
Author(s):  
D A Griffith ◽  
S M Jarvis
Keyword(s):  
Guinea Pig ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Hill Coefficient ◽  
Kidney Cortex ◽  
Pig Kidney ◽  
Na Ions

The characteristics of hypoxanthine transport were examined in purified brush-border membrane vesicles isolated from guinea-pig 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. Na(+)-dependent hypoxanthine influx was saturable (apparent Km 4.4 +/- 2.1 microM, Vmax. 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 (Ki values 1-30 microM), 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 (KNa 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.

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