Lipopolysaccharide (LPS)‐induced effects on Na+ transport and inflammatory response‐gene transcription in the guinea‐pig airway epithelium

Abstract

Earlier, we reported that systemic administration of LPS hyperpolarizes transepithelial potential difference (Vt). The increase in Vt was abolished by amiloride and inhibited by indomethacin. These findings suggested an increase in inflammatory‐mediator regulated Na+ transport. We investigated the effects of LPS on the mRNA levels of the epithelial sodium channel α subunit (αENaC), cyclooxygenase (COX) 2, endothelial nitric oxide synthase (eNOS), interleukin (IL)‐1β, inducible nitric oxide synthase (iNOS) and tumor necrosis factor (TNF)α, which regulate ENaC activity and turnover, using real‐time RT‐PCR. Guinea pigs received 4 mg/kg LPS (i.p.); epithelial cells (EC) and alveolar macrophages (AM) were examined after 3 or 18 h. EC COX2 increased by 36±26‐fold at 3 h and was elevated by 15±12‐fold at 18 h. In EC, TNFα, IL‐1β and iNOS were increased at 3 h (32±17‐, 25±12‐ and 7±5‐fold, respectively) and decreased to baseline after 18 h. AM COX2 was elevated at 3 (163±112‐fold) and 18 h (8±7‐fold). AM IL‐1β and AM TNFα were elevated at 3 h (127±60‐ and 20±7‐fold, respectively), and returned to baseline after 18 h. In contrast, AM eNOS increased by 4.7±5.4‐fold only at 18 h. The other transcripts were not increased more than 4‐fold in either tissue at 3 or 18 h. Thus, αENaC mRNA was not affected by LPS. An increase in ENaC transcription cannot explain the LPS‐induced increase in Vt.Funded by NIOSH.