Impairment of sodium-coupled uptakes by hydrogen peroxide in alveolar type II cells: protective effect of d-alpha-tocopherol.

Hydrogen peroxide (H2O2) is likely to play an important role in oxidant alveolar epithelium injury. We investigated the effect of H2O2 on uptake of phosphate, alanine in cultured rat alveolar type II cells. H2O2 induced inhibition of Na-dependent component of phosphate and alanine uptakes in time- and concentration-dependent manner. Twenty minutes exposure to 2.5 mM H2O2 decreased the maximum velocity (Vmax) of phosphate and alanine uptake by 50 and 62%, respectively, whereas Michaelis constant (Km) values were unchanged. H2O2 also decreased Na-K-ATPase activity, measured by ouabain-sensitive rubidium influx, and this effect was independent of H2O2-induced ATP depletion. A lipid-soluble antioxidant, d-alpha-tocopherol (20 microM, 24 h), prevented H2O2-induced decrease in Na-coupled uptake and Na-K-ATPase activity. These results indicate that H2O2 affects Na-dependent phosphate and alanine uptakes and suggest that this effect may be related at least, in part, to a decrease in Na transmembrane gradient, since H2O2 also affects Na-K-ATPase activity. The protective effect of d-alpha-tocopherol suggests that peroxidation of the membrane lipids is likely to be involved in the observed effects.