Lipopolysaccharide modifies amiloride-sensitive Na super(+) transport processes across human airway cells: role of mitogen-activated protein kinases ERK 1/2 and 5

Bacterial lipopolysaccharides (LPS) are potent inducers of proinflammatory signaling pathways via the activation of nuclear factor-kappa B (NF-B) and mitogen-activated protein kinase (MAPK), causing changes in the processes that control lung fluid homeostasis and contributing to the pathogenesis of lung disease. In human H441 airway epithelial cells, incubation of cells with 15kg ml super(-1) LPS caused a significant reduction in amiloride-sensitive I sub(sc) from 15c2 to 8c2kA cm super(-2) (p=0.01, n=13) and a shift in IC sub(50) amiloride of currents from 6.810 super(-7) to 6.410 super(-6)M. This effect was associated with a decrease in the activity of 5pS, highly Na super(+) selective, amiloride-sensitive 10kM cation channels (NSC) in the apical membrane. LPS decreased aENaC mRNA and protein abundance, inferring that LPS inhibited aENaC gene expression. This correlated with the decrease in HSC activity, indicating that these channels, but not NSCs, were comprised of at least aENaC protein. LPS increased NF-B DNA binding activity and phosphorylation of extracellular signal-related kinase (ERK)1/2, but decreased phosphorylation of ERK5 in H441 cells. Pretreatment of monolayers with PD98059 (20kM) inhibited ERK1/2 phosphorylation, promoted phosphorylation of ERK5, increased aENaC protein abundance, and reversed the effect of LPS on I sub(sc) and the shift in amiloride sensitivity. Inhibitors of NF-B activation were without effect. Taken together, our data indicate that LPS acts via ERK signaling pathways to decrease aENaC transcription, reducing HSC/ENaC channel abundance, activity, and transepithelial Na super(+) transport in H441 airway epithelial cells.