Abstract: | We evaluated theeffects of acute hyperoxic exposure on alveolar epithelial cell (AEC)active ion transport and on expression ofNa+ pump(Na+-K+-ATPase)and rat epithelial Na+ channelsubunits. Rat AEC were cultivated in minimal defined serum-free medium(MDSF) on polycarbonate filters. Beginning on day5, confluent monolayers were exposedto either 95% air-5% CO2(normoxia) or 95% O2-5%CO2 (hyperoxia) for 48 h.Transepithelial resistance(Rt) andshort-circuit current(Isc) weredetermined before and after exposure.Na+ channel -, -, and-subunit andNa+-K+-ATPase1- and1-subunit mRNA levels werequantified by Northern analysis.Na+ pump1- and1-subunit protein abundance wasquantified by Western blotting. After hyperoxic exposure,Isc across AECmonolayers decreased by ~60% at 48 h relative to monolayersmaintained under normoxic conditions.Na+ channel -subunit mRNAexpression was reduced by hyperoxia, whereas - and -subunit mRNAexpression was unchanged. Na+ pump1-subunit mRNA was unchanged,whereas 1-subunit mRNA was decreased ~80% by hyperoxia in parallel with a reduction in1-subunit protein. Becausekeratinocyte growth factor (KGF) has recently been shown to upregulateAEC active ion transport and expression ofNa+-K+-ATPaseunder normoxic conditions, we assessed the ability of KGF to preventhyperoxia-induced changes in active ion transport by supplementingmedium with KGF (10 ng/ml) from day2. The presence of KGF prevented theeffects of hyperoxia on ion transport (as measured byIsc) relativeto normoxic controls. Levels of1 mRNA and protein wererelatively preserved in monolayers maintained in MDSF and KGF comparedwith those cultivated in MDSF alone. These results indicate that AECnet active ion transport is decreased after 48 h of hyperoxia, likelyas a result of a decrease in the number of functionalNa+ pumps per cell. KGF largelyprevents this decrease in active ion transport, at least in part, bypreserving Na+ pump expression. |