Pulmonary, Gastrointestinal and Urogenital PharmacologyLipopolysaccharide increases Na+,K+-pump, but not ENaC, expression in guinea-pig airway epithelium

Earlier, we found in functional experiments that lipopolysaccharide (LPS; 4 mg/kg; i.p.) hyperpolarized the epithelium by stimulating the transepithelial transport of Na+ in guinea-pig tracheal epithelium. Epithelial sodium channel (ENaC) activity and Na+,K+-pump activity were increased. In this study, we hypothesized that LPS increases the expression of ENaC and the Na+,K+-pump in the epithelium and investigated the levels of transcription and protein abundance. Using qPCR, the effects of LPS on the transcription of αENaC, α1 Na+,K+-pump, COX-2, eNOS, iNOS, IL-1β, and TNF-α were measured at 3 and 18 h. In the epithelium, LPS increased the transcription of COX-2, IL-1β, and, to a nonsignificant extent, TNF-α at 3 h, but not at 18 h. In alveolar macrophages, TNF-α, and, to a nonsignificant extent, COX-2 and IL-1β were up-regulated at 3 h, but not at 18 h. Even though LPS stimulated the transcription of some genes, αENaC and α1 Na+,K+-ATPase transcription were not affected. The expressions of α-, β-, and γ-ENaC and α1 Na+,K+-pump from the tracheal epithelium and kidney cortex/medulla were investigated by western blotting. All three ENaC subunits were detected as cleavage fragments, yet LPS had no effect on their expression. LPS increased the expression of the α1 subunit and the α1, α2, and α3 subunits, collectively, of the Na+,K+-pump. Taken together, these data indicate that LPS increases Na+ transport downstream of the genetic level, in part, by stimulating the expression of the Na+,K+-pump.