Increase in endothelial cell glutathione and precursor amino acid uptake by diethyl maleate and hyperoxia

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Abstract
Diethyl maleate (DEM, 0.025-0.10 mM) increased glutathione (GSH) levels in calf pulmonary artery endothelial cells up to fivefold in 12-24 h of incubation. Parallel increases occurred in the rates of uptake of cystine and glutamate. The DEM-mediated increases in both GSH levels and glutamate-cystine uptake were inhibited by cycloheximide and actinomycin D, indicating a dependency on protein and RNA synthesis. The stimulatory effects of DEM on amino acid uptake and GSH levels were greater than those in endothelial cells exposed to 80% O2 for 24 h. The effect of hyperoxia on cellular transport processes was also less specific than that of DEM. Although the increase in glutamate uptake produced by hyperoxia appeared to be under the regulation of protein synthesis, the relationship with elevated GSH in the presence of hyperoxia was less clear because of elevation of control cellular GSH by cycloheximide or actinomycin D alone. Inhibition of GSH synthesis by buthionine sulfoximine also stimulated cystine and glutamate uptake. We conclude that elevation of endothelial intracellular GSH by both DEM and hyperoxia is associated with and may be produced by enhanced uptake of precursor amino acids; the effect of DEM is more pronounced and more specific than that of hyperoxia.