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Am J Physiol Cell Physiol 282: C1445-C1453, 2002. First published February 6, 2002; doi:10.1152/ajpcell.00410.2001
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Vol. 282, Issue 6, C1445-C1453, June 2002

Effect of reactive oxygen species on NH<UP><SUB>4</SUB><SUP>+</SUP></UP> permeation in Xenopus laevis oocytes

Marc Cougnon, Samia Benammou, Franck Brouillard, Philippe Hulin, and Gabrielle Planelles

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<UP><SUB>4</SUB><SUP>+</SUP></UP> permeation in Xenopus laevis oocytes, we used intracellular double-barreled microelectrodes to monitor the changes in membrane potential (Vm) and intracellular pH (pHi) induced by a 20 mM NH4Cl-containing solution. Under control conditions, NH4Cl exposure induced a large membrane depolarization (to Vm = 4.0 ± 1.5 mV; n = 21) and intracellular acidification [reaching a change in pHi (Delta pHi) of 0.59 ± 0.06 pH units in 12 min]; the initial rate of cell acidification (dpHi/dt) was 0.06 ± 0.01 pH units/min. Incubation of the oocytes in the presence of H2O2 or beta -amyloid protein had no marked effect on the NH4Cl-induced Delta pHi. 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 Delta pHi and dpHi/dt. These increases in Delta pHi and dpHi/dt were prevented by the ROS scavengers histidine and desferrioxamine, suggesting involvement of the reactive species 1Delta gO2 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 (Gm). This RB-induced Gm 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<UP><SUB>4</SUB><SUP>+</SUP></UP> influx into the oocyte via activation of a DPC-sensitive nonselective cation conductance pathway.

ammonium ions; nonselective cationic conductance


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