title: In vitro and in vivo regulation of transepithelial lung alveolar sodium transport by serine proteases.
abstract: The amiloride-sensitive epithelial sodium channel (ENaC) constitutes a rate-limiting step for sodium (Na+) and water absorption across lung alveolar epithelium. Recent reports suggested that ENaC is regulated by membrane-bound extracellular serine proteases, such as channel-activating proteases (CAPs). The objectives of this study were to examine the role of serine proteases in the regulation of transepithelial alveolar Na+ and water transport in vitro and in vivo and the expression of CAPs in rodent distal lung. In vitro experiments showed that inhibition of endogenous serine proteases by apical aprotinin 1) decreased ENaC-mediated currents in primary cultures of rat and mouse alveolar epithelial cells without affecting the abundance nor the electrophoretic migration pattern of biotinylated alpha- and beta-ENaC expressed at the cell surface and 2) suppressed the increase in amiloride-sensitive short-circuit current induced by the beta2-agonist terbutaline. RT-PCR experiments indicated that CAP1, CAP2, and CAP3 mRNAs were expressed in mouse alveolar epithelial cells, whereas CAP1 was also expressed in alveolar macrophages recovered by bronchoalveolar lavage. CAP1 protein was detected by Western blotting in rat and mouse alveolar epithelial cells, alveolar macrophages and bronchoalveolar lavage fluid. Finally, in vivo experiments revealed that intra-alveolar treatment with aprotinin abolished the increase in Na+-driven alveolar fluid clearance (AFC) induced by terbutaline in an in situ mouse lung model, whereas trypsin potentiated it. These results show that endogenous membrane-bound and/or secreted serine proteases such as CAPs regulate alveolar Na+ and fluid transport in vitro and in vivo in rodent lung.
authors.affiliation: Department of Physiology, INSERM U426, Faculté de Medécine Xavier Bichat, Université Paris 7, Paris, France. carole.planes@apr.ap-hop-paris.fr
authors.forename: Carole
authors.initials: C
authors.lastname: Planès
authors.forename: Céline
authors.initials: C
authors.lastname: Leyvraz
authors.forename: Tokujiro
authors.initials: T
authors.lastname: Uchida
authors.forename: Milena Apostolova
authors.initials: MA
authors.lastname: Angelova
authors.forename: Grégoire
authors.initials: G
authors.lastname: Vuagniaux
authors.forename: Edith
authors.initials: E
authors.lastname: Hummler
authors.forename: Michael
authors.initials: M
authors.lastname: Matthay
authors.forename: Christine
authors.initials: C
authors.lastname: Clerici
authors.forename: Bernard
authors.initials: B
authors.lastname: Rossier
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D007611:Aprotinin / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology*; D018893:Bronchoalveolar Lavage; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D003598:Cytoskeletal Proteins; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D053503:Epithelial Sodium Channels; D005260:Female; D066298:In Vitro Techniques; D016676:Macrophages, Alveolar / Q000166:cytology / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D015843:Serpins / Q000235:genetics / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*; D013726:Terbutaline / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology; D014867:Water / Q000378:metabolism
chemical_list: D000318:Adrenergic beta-Agonists; C081782:Cap1 protein, rat; C484230:Cap2 protein, rat; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D053503:Epithelial Sodium Channels; D008565:Membrane Proteins; D011506:Proteins; D012333:RNA, Messenger; D015842:Serine Proteinase Inhibitors; D015843:Serpins; D015222:Sodium Channels; D014867:Water; D007611:Aprotinin; D012964:Sodium; D012697:Serine Endopeptidases; C106610:Serpinb9 protein, mouse; C470745:Tmprss4 protein, mouse; D014357:Trypsin; D013726:Terbutaline