Earlier, we reported that systemic LPS administration increases transepithelial potential difference (Vt) in the guinea-pig trachea. The increase in Vt was abolished by the epithelial sodium channel (ENaC) blocker, amiloride, and inhibited by the prostaglandin synthase inhibitor, indomethacin. Here, we hypothesized that LPS increases Na+ absorption by increasing Na+, K+-ATPase activity. We investigated the effects of LPS on Vt using the isolated, perfused trachea preparation, which allows agents to be added to the luminal or the serosal surface. Eighteen hours after injection with LPS (4 mg/kg, ip), tracheas were removed, mounted on a holder, and perfused with Krebs solution. LPS increased basal Vt (-34.2 +/- 6.1 mV) compared to control (-5.5 +/- 1.8 mV, P < 0.05), consistent with increased cation absorption. Subsequently, apical amiloride (10 ÁM) reduced Vt to -4.5 +/- 2.2 in controls and to -13.1 +/- 2.9 in LPS-treated animals indicating increased flux of Na+ across the apical membrane. The cation pore-forming antifungal, amphotericin B (7.5 ÁM apically) then increased Vt to -18.9 +/- 2.7 in LPS-treated tracheas compared to -7.0 +/- 2.1 in controls. Vt after apical permeabilization is the result of basolateral ion transport and represents the maximum capacity of Na+, K+-ATPase. We conclude that LPS increases Na+ absorption, at least in part, via ENaC by increasing the activity of the Na+, K+-ATPase.
The FASEB Journal. Experimental Biology 2009, April 18 - 22, 2009, New Orleans, Louisiana