Abstract

The acute respiratory distress syndrome is characterized by impairment of the alveolar-capillary barrier. Our laboratory has shown that distal lung epithelial cell (DLEC) amiloride-sensitive Na+ transport is impaired by in vitro coculture with endotoxin (lipopolysaccharide)-stimulated alveolar macrophages (AM) through an L-arginine-dependent mechanism. To investigate the effect 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 microg/mL), or the cell-free supernatant of lipopolysaccharide-stimulated rat AM. Such exposure resulted in a profound decrease in mRNA expression for all subunits (alpha, beta, and gamma) of the rat epithelial Na+ channel, without affecting 18S RNA levels. This effect was prevented by the antioxidant N-acetylcysteine. In separate experiments, confluent DLEC monolayers were exposed to lipopolysaccharide-stimulated AM supernatant for 16 h with or without N-acetylcysteine and DTT and studied in Ussing 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-circuit current (control, 3.96 +/- 0.18 microA/cm2 versus supernatant, 2.34 +/- 0.56 microA/cm2; p < 0.05). This effect was significantly reversed by N-acetylcysteine (3.55 +/- 0.48 microA/cm2), but not by DTT (1.87 +/- 0.21 microA/cm2). N-acetylcysteine, but not DTT, increased DLEC thiol levels. These studies elucidate mechanisms by which activated AM impair alveolar epithelial barrier function in an in vitro model of acute lung injury.

View details for Web of Science ID 000088845900008

View details for PubMedID 10960494