OBJECTIVETo evaluate the capacity of alveolar type II (AT II) cells for water and sodium transport in rats with early-stage oleic acid-induced acute lung injury (ALI)/acute respiratory distress syndrome (ARDS).

METHODSAT II cells were isolated and purified from rats with ALI/ARDS induced by oleic acid, and their morphology was observed using electron microscopy and optical microscopy. The extravascular lung water (EVLW) content in the rats was measured by gravimetric method. The distribution of aquaporin-4 (AQP-4) on the cell membrane was observed with immunohistochemistry, and the expression of AQP-4 mRNA was detected with RT-PCR.

RESULTSMicroscopic examination and blood gas analysis indicated severe injury of the lung tissues in ALI group. Smith lung injury score and EVLW in ALI group were significantly higher in ALI group than in the control group (P<0.05). Immunohistochemistry identified intensified AQP-4 expression in rat lung tissues and RT-PCR also demonstrated increased AQP-4 mRNA expression as compared with the control group. The level of APQ-4 whole-cell currents was decreased in AT II cell membrane and increased in cytoplasm in ALI group (P<0.05 ).

CONCLUSIONSPathophysiological changes occurs in early stage of oleic acid-induced AMI, and AQP-4 mRNA expression is up-regulated on the AT II cell membrane to regulate the exchange of fluid between the alveolar space and alveolar epithelium barrier and play an important compensational role in pulmonary liquid clearance in the event of sodium transport damages in ALI.