Inhibition of amiloride-sensitive sodium-channel activity in distal lung epithelial cells by nitric oxide

Abstract

Distal lung epithelial cells (DLECs) play an active role in fluid clearance from the alveolus by virtue of their ability to actively transport Na+ from the alveolus to the interstitial space. The present study evaluated the ability of activated macrophages to modulate the bioelectric properties of DLECs. Low numbers of lipopolysaccharide (LPS)-treated macrophages were able to significantly reduce amiloride-sensitive short-circuit current ( I sc) without affecting total I sc or monolayer resistance. This was associated with a rise in the flufenamic acid-sensitive component of the I sc. The effect was reversed by the addition of N-monomethyl-l-arginine to the medium, implying a role for nitric oxide. We hypothesized that macrophages exerted their effect by expressing inducible nitric oxide synthase (iNOS) in DLECs. The products of LPS-treated macrophages increased the levels of iNOS protein and mRNA transcripts in DLECs as well as causing a rise in iNOS activity. Immunofluorescence microscopy of LPS-stimulated macrophage-DLEC cocultures with anti-nitrotyrosine antibodies provided evidence for the generation of peroxynitrite in macrophages but not in DLECs. These data indicate that activated macrophages in the lung may contribute to impaired resolution of acute respiratory distress syndrome and suggest a novel mechanism whereby nitric oxide might alter cell function by altering its ion-transporting phenotype.

Acute Lung Injury Edema Fluid Decreases Net Fluid Transport across Human Alveolar Epithelial Type II Cells

“…Although we primarily studied the role of the inflammatory cytokines in this study, ALI pulmonary edema fluid contains other biologically active substances such as proteolytic enzymes, lipids, and reactive oxygen species, particularly the NO metabolite peroxynitrite, which can affect not only fluid clearance but other alveolar epithelial type II cell activity such as surfactant homeostasis. In a similar model in the rat, O'Brodovich and co-workers (45)(46)(47)(48) found that endotoxinstimulated alveolar macrophages or the corresponding supernatant decreases ENaC mRNA levels and activity as well as amiloride-sensitive sodium channel activity among distal lung epithelial cells. The inhibitory effect is prevented by the addition of a nitric-oxide synthase inhibitor or an antioxidant.…”

Apical, But Not Basolateral, Endotoxin Preincubation Protects Alveolar Epithelial Cells Against Hydrogen Peroxide-Induced Loss of Barrier Function: The Role of Nitric Oxide Synthesis

“…to form peroxynitrite may cause oxidation of protein and non-protein sulfhydryl groups and may enhance lipid peroxidation, thereby promoting tissue injury (35). Concerning the currently investigated alveolar epithelial cells, NO/peroxynitrite was found to suppress the activity of sodium permeant cation and L-type calcium channels on the apical surface, as well as the basolaterally located Na Ϯ K ϩ ATPase (36,37). Moreover, high concentrations of NO deteriorate the biophysical function of the type II cell-derived pulmonary surfactant system, which again was ascribed to NO-related peroxynitrite formation (38,39), and NO was found to decrease ATP content and surfactant synthesis in freshly isolated ATII (40,41).…”

Histone H1.2 is a substrate for denitrase, an activity that reduces nitrotyrosine immunoreactivity in proteins

“…2, double asterisk). This might be caused by nitration during the membrane incubation because LPS treatment is known to increase nitrotyrosine immunoreactivity in macrophages (29).…”