Lipopolysaccharide increases Na+,K+-pump, but not ENaC, expression in guinea-pig airway epithelium
Dodrill, MW; Beezhold, DH; Meighan, T; Kashon, ML; Fedan, JS
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 alpha ENaC, alpha(1) Na+, K+-pump, COX-2, eNOS, iNOS, IL-1 beta, and TNF-alpha
were measured at 3 and 18 h. In the epithelium, LPS increased the transcription of COX-2. IL-1
beta, and, to a nonsignificant extent, TNF-alpha at 3 h, but not at 18 h. In alveolar
macrophages, TNF-alpha, and, to a nonsignificant extent, COX-2 and IL-1 beta were up-regulated at
3 h, but not at 18 h. Even though LPS stimulated the transcription of some genes, alpha ENaC and
alpha(1) Na+,K+-ATPase transcription were not affected. The expressions of alpha-, beta-, and
gamma-ENaC and alpha(1) 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 alpha(1) subunit
and the alpha(1), alpha(2), and alpha(3) 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. Published by Elsevier B.V.
Endotoxin; Lung; Airway epithelium; Epithelial sodium channel (ENaC); Sodium, Potassium ATPase (Na+,K+-ATPase)