Plasmin in nephrotic urine activates the epithelial sodium channel.
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.
Svenningsen
Per
P
Physiology and Pharmacology, Institute of Medical Biology, University of Southern Denmark, Odense C.
Bistrup
Claus
C
Friis
Ulla G
UG
Bertog
Marko
M
Haerteis
Silke
S
Krueger
Bettina
B
Stubbe
Jane
J
Jensen
Ole Nørregaard
ON
Thiesson
Helle C
HC
Uhrenholt
Torben R
TR
Jespersen
Bente
B
Jensen
Boye L
BL
Korbmacher
Christoph
C
Skøtt
Ole
O
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
D053503:Epithelial Sodium Channels; D000584:Amiloride; D010958:Plasminogen; D010447:Peptide Hydrolases; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator