AQP5 and bronchopulmonary dysplasia: Since impaired alveolar growth is a key characteristic of lungs with BPD, and epithelial cells are central in the process of alveolar growth, we next investigated alveolar epithelial cell markers, including aquaporin 5 (AQP5) as a marker for ATI, and surfactant protein C (SFTPC) as a marker for ATII cells in total lung homogenates of mice exposed to short-term HYX (P7), prolonged HYX (P28), and after recovery in room air (P70).