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Effect of reactive oxygen species on NH4+ permeation in Xenopus laevis oocytes

Institut National de la Santé et de la Recherche Médicale Unité 467, Université Paris V, Faculté de Médecine Necker-Enfants Malades, 75730 Paris Cedex 15, France To investigate the effects of reactive oxygen species (ROS) on NH permeation in Xenopus laevis oocytes, we used intracellular double-barre...

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Published in:American Journal of Physiology: Cell Physiology 2002-06, Vol.282 (6), p.C1445
Main Authors: Cougnon, Marc, Benammou, Samia, Brouillard, Franck, Hulin, Philippe, Planelles, Gabrielle
Format: Article
Language:English
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Summary:Institut National de la Santé et de la Recherche Médicale Unité 467, Université Paris V, Faculté de Médecine Necker-Enfants Malades, 75730 Paris Cedex 15, France To investigate the effects of reactive oxygen species (ROS) on NH permeation in Xenopus laevis oocytes, we used intracellular double-barreled microelectrodes to monitor the changes in membrane potential ( V m ) and intracellular pH (pH i ) induced by a 20 mM NH 4 Cl-containing solution. Under control conditions, NH 4 Cl exposure induced a large membrane depolarization (to V m  = 4.0 ± 1.5 mV; n  = 21) and intracellular acidification [reaching a change in pH i ( pH i ) of 0.59 ± 0.06 pH units in 12   min]; the initial rate of cell acidification (dpH i /d t ) was 0.06   ± 0.01 pH units/min. Incubation of the oocytes in the presence of H 2 O 2 or -amyloid protein had no marked effect on the NH 4 Cl-induced pH i . By contrast, in the presence of photoactivated rose bengal (RB), tert -butyl-hydroxyperoxide ( t -BHP), or xanthine/xanthine oxidase (X/XO), the same experimental maneuver induced significantly greater pH i and dpH i /d t . These increases in pH i and dpH i /d t were prevented by the ROS scavengers histidine and desferrioxamine, suggesting involvement of the reactive species 1 gO 2 and ·OH. Using the voltage-clamp technique to identify the mechanism underlying the ROS-measured effects, we found that RB induced a large increase in the oocyte membrane conductance ( G m ). This RB-induced G m increase was prevented by 1 mM diphenylamine-2-carboxylate (DPC) and by a low Na + concentration in the bath. We conclude that RB, t -BHP, and X/XO enhance NH influx into the oocyte via activation of a DPC-sensitive nonselective cation conductance pathway. ammonium ions; nonselective cationic conductance
ISSN:0363-6143
1522-1563
DOI:10.1152/ajpcell.00410.2001