Patient with acute respiratory distress syndrome (ARDS) have their airspaces flooded with edema from pulmonary capillaries thus compromising oxygen transfer from the airspaces into the systemic circulation. Recent investigations have demonstrated the importance of active sodium transport and lung edema clearance in the survival of patients with respiratory failure. The Na,K-ATPase regulates edema clearance across the alveolar epithelium. It has been shown that hypoxia inhibits ion transport and impairs lung edema clearance by yet unclear mechanisms. We sought to study whether hypoxia induces Na,K-ATPase degradation in alveolar epithelial cells (AEC) via the ubiquitin/proteasome or lysosomal pathways. Our preliminary data shows that Na,K-ATPase half life is decreased in the presence of hypoxia (1.5% O2) and its degradation is blocked by proteasomal and lysosomal inhibitors. The specific aims of this proposal are Specific aim # 1:To determine whether hypoxia increases Na,K-ATPase degradation via ubiquitin pathway. Specific aim #2: To determine whether hypoxia increases Na,K-ATPase degradation via the lysosome or proteasome system. Specific aim #3: To determine the E-2s and E-3s enzymes involved in the degradation process of the Na,K-ATPase. Completion of the proposed studies will provide novel information on the effects of hypoxia, specifically as it pertains to mechanisms of inhibition and degradation of the Na,K-ATPase as well as pathways of reversal Na,K-ATPase inhibitions, which may be of relevance for the design of novel strategies to increase alveolar fluid clearance in patients with hypoxemic respiratory failure.