Effect of medium pH on glutathione redox cycle in cultured human umbilical vein endothelial cells

Impairments of the glutathione redox cycle in cultured endothelial cells under acidic pH conditions were measured. Glutathione-dependent H2O2-degrading activities decreased by 20% (P < .01) at pH 6 and by 51% (P < .01) at pH 4 compared with activities at pH 7.4 1 hour after a change with fresh medium. Intracellular reduced glutathione (GSH) content increased by 85% (P < .01) following the change with pH 7.4 medium. Such increases in GSH content were impaired after exposure to acidic medium. After exposure to 500 mumol/LH2O2, intracellular GSH content decreased by 61% compared with the level obtained in the absence of H2O2 at pH 7.4 (P < .01). Compared with the level at pH 7.4, the H2O2-induced decrease in intracellular GSH content was 32% lower (P < .01) at pH 6 and did not change at all at pH 4. After exposure to 500 mumol/L H2O2, the intracellular oxidized glutathione (GSSG) content increased by 160% at pH 7.4 (P < .01), 370% at pH 6 (P < .01), and 90% at pH 4 compared with treatment without H2O2, respectively. After exposure to 500 mumol/L H2O2, the release of GSSG from cells at pH 6 decreased by 38% compared with the value found at pH 7.4 (P < .05), and the release at pH 4 completely disappeared. Both glutathione peroxidase (GPO) and glutathione reductase activities decreased as a function of a decrease in pH from 7.4 to 4.(ABSTRACT TRUNCATED AT 250 WORDS)