title: Endotoxin-stimulated alveolar macrophages impair lung epithelial Na+ transport by an L-Arg-dependent mechanism.
abstract: The Na+ transport function of alveolar epithelium represents an important mechanism for air space fluid clearance after acute lung injury. We studied the effect of endotoxin-stimulated rat alveolar macrophages on lung epithelial ion transport and permeability in vitro. Cultured rat distal lung (alveolar) epithelial monolayers incubated with both endotoxin and macrophages demonstrated a 75% decline in transepithelial resistance and a selective 60% reduction in amiloride-sensitive short-circuit current (Isc). Single-channel patch-clamp analysis demonstrated a 60% decrease in the density of 25-pS nonselective cation (NSC) channels on the apical membrane of epithelium exposed to both endotoxin and macrophages. A concurrent reduction in epithelial F-actin content suggested a role for actin depolymerization in mediating this effect. Incubation of cocultures with the methylated L-arginine (Arg) derivative NG-monomethyl-L-arginine prevented the reduction in epithelial Isc, as did substitution of L-Arg with D-Arg or incubation in L-Arg-free medium. Furthermore, the stable and products of Arg metabolism were found to have no effect on epithelial ion transport. These studies show that endotoxin-stimulated alveolar macrophages impair distal lung epithelial ion transport by an L-Arg-dependent mechanism by inactivating amiloride-sensitive 25-pS NSC channels. This may represent a novel mechanism whereby local inflammatory cells regulate lung epithelial ion transport. This could affect the ability of the lung to clear fluid from the air space.
authors.affiliation: Department of Surgery, Toronto General Hospital, Ontario, Canada.
authors.forename: C G
authors.initials: CG
authors.lastname: Compeau
authors.forename: O D
authors.initials: OD
authors.lastname: Rotstein
authors.forename: H
authors.initials: H
authors.lastname: Tohda
authors.forename: Y
authors.initials: Y
authors.lastname: Marunaka
authors.forename: B
authors.initials: B
authors.lastname: Rafii
authors.forename: A S
authors.initials: AS
authors.lastname: Slutsky
authors.forename: H
authors.initials: H
authors.lastname: O'Brodovich
mesh_terms: D000225:Adenine / Q000378:metabolism; D000818:Animals; D001120:Arginine / Q000494:pharmacology* / Q000502:physiology*; D001693:Biological Transport, Active / Q000187:drug effects; D002450:Cell Communication; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002463:Cell Membrane Permeability; D002469:Cell Separation / Q000379:methods; D002470:Cell Survival; D002478:Cells, Cultured; D004731:Endotoxins / Q000633:toxicity; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D015640:Ion Channel Gating; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology; D007536:Isomerism; D008070:Lipopolysaccharides / Q000633:toxicity*; D008168:Lung / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D016676:Macrophages, Alveolar / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*
chemical_list: D004731:Endotoxins; D007473:Ion Channels; D008070:Lipopolysaccharides; D001120:Arginine; D012964:Sodium; D000225:Adenine