HYDROGEN-PEROXIDE INCREASES NA+ K+-ATPASE FUNCTION IN ALVEOLAR TYPE-II CELLS/

We have studied the regulation of Na+/K+-ATPase function in alveolar t ype II cells submitted to oxidative stress, Alveolar type II cells wer e isolated from Sprague Dawley rats and suspended in Dulbecco's modifi ed Eagle's medium. 500 mu M xanthine plus 0.5 or 5 mU/ml xanthine oxid ase (group 1 and 2, respectively) were added to the cell suspensions, Following various exposure times the reaction was stopped by adding al lopurinol and cells were processed to assay H2O2 steady state concentr ations, enzymatic activity of catalase and Na+/K+-ATPase function. Hyd rogen peroxide production by the xanthine-xanthine oxidase system reac hed maximal values at 30 min of incubation in both groups, H2O2 steady state concentration increased 2- and 10-fold, respectively. Catalase activity was not changed after slight oxidative stress (group 1) but d ecreased in severe oxidative stress (group 2), Decreases in the Na+/K-ATPase activity (10 and 60% for groups 1 and 2) were found during the first hour of exposure coinciding with the peak in H2O2 steady state concentration. This early inactivation was followed by progressive inc reases in the activity up to 70% over the control value in group 1, an d to the control value in group 2. [H-3]Ouabain binding studies showed that the increase in Na+/K+-ATPase activity after oxidative stress wa s due to an increase in the number of phosphorylated pump molecules in the plasma membrane of alveolar type II cells.