title: Plasmin in nephrotic urine activates the epithelial sodium channel.
abstract: Proteinuria and increased renal reabsorption of NaCl characterize the nephrotic syndrome. Here, we show that protein-rich urine from nephrotic rats and from patients with nephrotic syndrome activate the epithelial sodium channel (ENaC) in cultured M-1 mouse collecting duct cells and in Xenopus laevis oocytes heterologously expressing ENaC. The activation depended on urinary serine protease activity. We identified plasmin as a urinary serine protease by matrix-assisted laser desorption/ionization time of-flight mass spectrometry. Purified plasmin activated ENaC currents, and inhibitors of plasmin abolished urinary protease activity and the ability to activate ENaC. In nephrotic syndrome, tubular urokinase-type plasminogen activator likely converts filtered plasminogen to plasmin. Consistent with this, the combined application of urokinase-type plasminogen activator and plasminogen stimulated amiloride-sensitive transepithelial sodium transport in M-1 cells and increased amiloride-sensitive whole-cell currents in Xenopus laevis oocytes heterologously expressing ENaC. Activation of ENaC by plasmin involved cleavage and release of an inhibitory peptide from the ENaC gamma subunit ectodomain. These data suggest that a defective glomerular filtration barrier allows passage of proteolytic enzymes that have the ability to activate ENaC.
authors.affiliation: Physiology and Pharmacology, Institute of Medical Biology, University of Southern Denmark, Odense C.
authors.forename: Per
authors.initials: P
authors.lastname: Svenningsen
authors.forename: Claus
authors.initials: C
authors.lastname: Bistrup
authors.forename: Ulla G
authors.initials: UG
authors.lastname: Friis
authors.forename: Marko
authors.initials: M
authors.lastname: Bertog
authors.forename: Silke
authors.initials: S
authors.lastname: Haerteis
authors.forename: Bettina
authors.initials: B
authors.lastname: Krueger
authors.forename: Jane
authors.initials: J
authors.lastname: Stubbe
authors.forename: Ole Nørregaard
authors.initials: ON
authors.lastname: Jensen
authors.forename: Helle C
authors.initials: HC
authors.lastname: Thiesson
authors.forename: Torben R
authors.initials: TR
authors.lastname: Uhrenholt
authors.forename: Bente
authors.initials: B
authors.lastname: Jespersen
authors.forename: Boye L
authors.initials: BL
authors.lastname: Jensen
authors.forename: Christoph
authors.initials: C
authors.lastname: Korbmacher
authors.forename: Ole
authors.initials: O
authors.lastname: Skøtt
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D005341:Fibrinolysin / Q000652:urine*; D006801:Humans; D007668:Kidney / Q000378:metabolism; D051379:Mice; D009401:Nephrosis / Q000652:urine*; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010447:Peptide Hydrolases / Q000378:metabolism; D010958:Plasminogen / Q000378:metabolism; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D053503:Epithelial Sodium Channels; D000584:Amiloride; D010958:Plasminogen; D010447:Peptide Hydrolases; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator