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 subunit (ENaC), cyclooxygenase (COX) 2, endothelial nitric oxide synthase (eNOS), interleukin (IL)-1ß, inducible nitric oxide synthase (iNOS) and tumor necrosis factor (TNF)alpha, 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, TNFalpha, IL-1ß 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-1ß and AM TNFalpha 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, ENaC mRNA was not affected by LPS. An increase in ENaC transcription cannot explain the LPS-induced increase in Vt.
The FASEB Journal. Experimental Biology 2008, April 5 - 9, 2008, San Diego, California