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Articles in PresS, published online ahead of print February 6, 2002
Am J Physiol Cell Physiol, 10.1152/ajpcell.00410.2001
Submitted on August 22, 2001
Accepted on February 1, 2002
1 U 467, Inserm, Paris, France
* To whom correspondence should be addressed. E-mail: planelle{at}necker.fr.
To investigate the effects of reactive oxygen species (ROS) on NH4+ permeation in Xenopus laevis oocytes, we used intracellular double-barreled microelectrodes to monitor the changes in membrane potential (Vm) and in 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 
pHi of 0.59 ± 0.06 U pH in 12 min); the initial rate of cell acidification (dpHi/dt) was 0.06 ± 0.01 U pH/min. Incubation of the oocytes in the presence of H2O2 or ß-amyloid protein had no marked effect on the NH4Cl-induced pHi change. By contrast, in the presence of photoactivated Rose Bengal (RB), tert-butyl-hydroxyperoxyde (t-BHP), or xanthine/xanthine oxydase (X/XO), the same experimental maneuver induced significantly greater pHi and dpHi/dt. These increases in pHi and dpHidt were prevented by the ROS scavengers histidine and desferroxamine, suggesting involvement of the reactive species 1gO2 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 diphenyl-amine-2-carboxylate (DPC) and by a low Na+ concentration in the bath. We conclude that RB, t-BHP, and X/XO enhance NH4+ influx into the oocyte via activation of a DPC-sensitive non-selective cation conductance pathway.
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