Aj. Dickie et al., Preventing endotoxin-stimulated alveolar macrophages from decreasing epithelium Na+ channel (ENaC) mRNA levels and activity, PEDIAT RES, 48(3), 2000, pp. 304-310
The acute respiratory distress syndrome is characterized by impairment of t
he alveolar-capillary barrier. Our laboratory has shown that distal lung ep
ithelial cell (DLEC) amiloride-sensitive Na+ transport is impaired by in vi
tro coculture with endotoxin (lipopolysaccharide)-stimulated alveolar macro
phages (AM) through an L-areinine-dependent mechanism. To investigate the e
ffect of this model on mRNA levels of the rat epithelial Na+ channel mature
fetal rat DLEC monolayers were incubated for 16 h with rat AM (1 X 10(7))
and lipopolysaccharide (10 mu g/mL), or the cell-free supernatant of lipopo
lysaccharide-stimulated rat AM. Such exposure resulted in a profound decrea
se in mRNA expression for all subunits (alpha, beta, and gamma) of the mt e
pithelial Na+ channel, without affecting 18S RNA levels. This effect was pr
evented by the antioxidant N-acetylcysteine. In separate experiments, confl
uent DLEC monolayers were: exposed to lipopolysaccharide-stimulated AM supe
rnatant for 16 h with or without N-acetylcysteine and DTT and studied in Us
sing chambers. As previously demonstrated in our laboratory, AM supernatant
resulted in a significant (p < 0.05) impairment of DLEC Na+ transport, as
reflected by a decrease in the amiloride-sensitive component of short-circu
it current (control, 3.96 +/- 0.18 mu A/cm(2) vesus supernatant, 2.34 +/- 0
.56 mu A/cm(2); p < 0.05). This effect was significantly reversed by N-acet
ylcysteine (3.55 +/- 0.48 mu A/cm(2)), but not by DTT (1.87 +/- 0.21 mu A/c
m(2)). N-acetylcysteine, but not DTT, increased DLEC thiol levels. These st
udies elucidate mechanisms by which activated BM impair alveolar epithelial
barrier function in an b vitro model of acute lung injury.