Na+-K+-ATPase expression in alveolar epithelial cells: upregulation of active ion transport by KGF.

We evaluated the effects of keratinocyte growth factor (KGF) on alveolar epithelial cell (AEC) active ion transport and on rat epithelial Na channel (rENaC) subunit and Na+-K+-adenosinetriphosphatase (ATPase) subunit isoform expression using monolayers of AEC grown in primary culture. Rat alveolar type II cells were plated on polycarbonate filters in serum-free medium, and KGF (10 ng/ml) was added to confluent AEC monolayers on day 4 in culture. Exposure of AEC monolayers to KGF on day 4 resulted in dose-dependent increases in short-circuit current ( I sc) compared with controls by day 5, with further increases occurring through day 8. Relative Na+-K+-ATPase α1-subunit mRNA abundance was increased by 41% on days 6 and 8 after exposure to KGF, whereas α2-subunit mRNA remained only marginally detectable in both the absence and presence of KGF. Levels of mRNA for the β1-subunit of Na+-K+-ATPase did not increase, whereas cellular α1- and β1-subunit protein increased 70 and 31%, respectively, on day 6. mRNA for α-, β-, and γ-rENaC all decreased in abundance after treatment with KGF. These results indicate that KGF upregulates active ion transport across AEC monolayers via a KGF-induced increase in Na pumps, primarily due to increased Na+-K+-ATPase α1-subunit mRNA expression. We conclude that KGF may enhance alveolar fluid clearance after acute lung injury by upregulating Na pump expression and transepithelial Na transport across the alveolar epithelium.