Alpha(1)-antitrypsin inhibits epithelial Na+ transport in vitro and in vivo.
A variety of studies have shown that Na(+) reabsorption across epithelial cells depends on the protease-antiprotease balance. Herein, we investigate the mechanisms by which alpha(1)-antitrypsin (A1AT), a major anti-serine protease in human plasma and lung epithelial fluid and lacking a Kunitz domain, regulates amiloride-sensitive epithelial Na(+) channel (ENaC) function in vitro and in vivo. A1AT (0.05 mg/ml = 1 microM) decreased ENaC currents across Xenopus laevis oocytes injected with human alpha,beta,gamma-ENaC (hENaC) cRNAs, and human lung Clara-like (H441) cells expressing native ENaC, in a partially irreversible fashion. A1AT also decreased ENaC single-channel activity when added in the pipette but not in the bath solutions of ENaC-expressing oocytes patched in the cell-attached mode. Incubation of A1AT with peroxynitrite (ONOO(-)), an oxidizing and nitrating agent, abolished its antiprotease activity and significantly decreased its ability to inhibit ENaC. Intratracheal instillation of normal but not ONOO(-)-treated A1AT (1 microM) in C57BL/6 mice also decreased Na(+)-dependent alveolar fluid clearance to the same level as amiloride. Incubation of either H441 cells or ENaC-expressing oocytes with normal but not ONOO(-)-treated A1AT decreased their ability to cleave a substrate of serine proteases. A1AT had no effect on amiloride-sensitive currents of oocytes injected with hENaC bearing Liddle mutations, presumably because these channels remain at the surface longer than the wild-type channels. These data indicate that A1AT may be an important modulator of ENaC activity and of Na(+)-dependent fluid clearance across the distal lung epithelium in vivo by decreasing endogenous protease activity needed to activate silent ENaC.
Lazrak
Ahmed
A
Department of Anesthesiology, University of Alabama at Birmingham, 224 BMR II, 901 South 19th Street, Birmingham, AL 35205-3703, USA.
Nita
Izabella
I
Subramaniyam
Devipriya
D
Wei
Shipeng
S
Song
Weifeng
W
Ji
Hong-Long
HL
Janciauskiene
Sabina
S
Matalon
Sadis
S
D000818:Animals; D002460:Cell Line; D004847:Epithelial Cells / Q000378:metabolism; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D018408:Patch-Clamp Techniques; D030421:Peroxynitrous Acid / Q000378:metabolism; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000166:cytology* / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D014982:Xenopus laevis; D000515:alpha 1-Antitrypsin / Q000235:genetics / Q000378:metabolism*
D053503:Epithelial Sodium Channels; D021122:Protein Subunits; D000515:alpha 1-Antitrypsin; D030421:Peroxynitrous Acid; D012964:Sodium