Most patients with
acute lung injury (ALI) have reduced alveolar fluid clearance that has been associated with higher mortality. Several mechanisms may contribute to the decrease in alveolar fluid clearance. In this study, we tested the hypothesis that
pulmonary edema fluid from patients with ALI might reduce the expression of ion transport genes responsible for vectorial fluid transport in primary cultures of human alveolar epithelial type II cells. Following exposure to ALI
pulmonary edema fluid, the gene copy number for the major
sodium and
chloride transport genes decreased. By Western blot analyses,
protein levels of alphaENaC, alpha1Na,K-ATPase, and
cystic fibrosis transmembrane conductance regulator decreased as well. In contrast, the gene copy number for several inflammatory
cytokines increased markedly. Functional studies demonstrated that net vectorial fluid transport was reduced for human alveolar type II cells exposed to ALI
pulmonary edema fluid compared with plasma (0.02 +/- 0.05 versus 1.31 +/- 0.56 microl/cm2/h, p < 0.02). An inhibitor of
p38 MAPK phosphorylation (
SB202190) partially reversed the effects of the
edema fluid on net fluid transport as well as gene and
protein expression of the main ion transporters. In summary, alveolar
edema fluid from patients with ALI induced a significant reduction in
sodium and
chloride transport genes and
proteins in human alveolar epithelial type II cells, effects that were associated with a decrease in net vectorial fluid transport across human alveolar type II cell monolayers.