PEROXYNITRITE INHIBITION OF OXYGEN-CONSUMPTION AND SODIUM-TRANSPORT IN ALVEOLAR TYPE-II CELLS

Active sodium (Na+) transport by alveolar type II (ATII) cells plays an important role in limiting the volume of alveolar fluid. Reactive oxygen and nitrogen species, released in the epithelial lining fluid by activated inflammatory cells or present in inspired gases, may damage Na+ transporters and decrease fluid reabsorption. To test this hypothesis we exposed ATII cells to xanthine and xanthine oxidase (1 or 10 mU/ml), or to boluses of peroxynitrite (0.1-1 mM final concentration) for 15 min and measured 1) cellular oxygen consumption (VO2); 2) amiloride-inhibitable Na-22(+) uptake, as an index of Na+ movement through apically located Na+ channels; and 3) ouabain-sensitive Rb-86(+) uptake, as an index of the activity of the basolaterally located Na+-K+-ATPase. After exposure of ATII cells to 0.5 or 1 mM peroxynitrite, amiloride-inhibitable Na-22(+) uptake decreased to 68 +/- 7 and 56 +/- 11 of their control values, respectively (means +/- SE; n greater than or equal to 6). Exposure to 0.5 mM peroxynitrite decreased ATII cell VO2 from 76 +/- 6 to 25 +/- 5 mu M.h(-1).-10(6) cells(-1) (means +/- SE; n = 5). Cell viability and ouabain-sensitive Rb-86(+) uptake remained at control levels for either peroxynitrite concentration. Exposure of ATII cells to 10 mU/ml xanthine oxidase decreased their VO2 from 94 +/- 8 to 63 +/- 6 (means +/- SE; n = 5), but did not alter amiloride-inhibitable Na-22(+) uptake. These findings indicate that physiological concentrations of peroxynitrite, but not of reactive oxygen species, decrease ATII cell Na+ transport by damaging apically located amiloride-sensitive Na+ channels.