Effect of reactive oxygen species on N[H.sup.+.sub.4] permeation in Xenopus laevis oocytes

To investigate the effects of reactive oxygen species (ROS) on N[H.sup.+.sub.4] permeation in Xenopus laevis oocytes, we used intracellular double-barreled microelectrodes to monitor the changes in membrane potential ([V.sub.m]) and intracellular pH (p[H.sub.i]) induced by a 20 mM N[H.sub.4]Cl-containing solution. Under control conditions, N[H.sub.4]Cl exposure induced a large membrane depolarization (to [V.sub.m] = 4.0 [+ or -] 1.5 mV; n = 21) and intracellular acidification [reaching a change in p[H.sub.i] ([DELTA]p[H.sub.i]) of 0.59 [+ or -] 0.06 pH units in 12 min]; the initial rate of cell acidification (dp[H.sub.i]/dt) was 0.06 [+ or -] 0.01 pH units/min. Incubation of the oocytes in the presence of [H.sub.2][O.sub.2] or [beta]-amyloid protein had no marked effect on the N[H.sub.4]Cl-induced [DELTA]p[H.sub.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 [DELTA]p[H.sub.i] and dp[H.sub.i]/dt. These increases in [DELTA]p[H.sub.i] and dp[H.sub.i]/dt were prevented by the ROS scavengers histidine and desferrioxamine, suggesting involvement of the reactive species [sup.1][DELTA]G[O.sub.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.sub.m]). This RB-induced [G.sub.m] increase was prevented by 1 mM diphenylamine-2-carboxylate (DPC) and by a low [Na.sup.+] concentration in the bath. We conclude that RB, t-BHP, and X/XO enhance N[H.sup.+.sub.4] influx into the oocyte via activation of a DPC-sensitive nonselective cation conductance pathway. ammonium ions; nonselective cationic conductance