Low expression of the beta-ENaC subunit impairs lung fluid clearance in the mouse.
Transepithelial alveolar sodium (Na+) transport mediated by the amiloride-sensitive epithelial sodium channel (ENaC) constitutes the driving force for removal of fluid from the alveolar space. To define the role of the beta-ENaC subunit in vivo in the mature lung, we studied a previously established mouse strain harboring a disruption of the beta-ENaC gene locus resulting in low levels of beta-ENaC mRNA expression. Real-time RT-PCR experiments confirmed that beta-ENaC mRNA levels were decreased by >90% in alveolar epithelial cells from homozygous mutant (m/m) mice. beta-ENaC protein was undetected in lung homogenates from m/m mice by Western blotting, but alpha- and gamma-ENaC proteins were increased by 83% and 45%, respectively, compared with wild-type (WT) mice. At baseline, Na+-driven alveolar fluid clearance (AFC) was significantly reduced by 32% in m/m mice. Amiloride at the concentration 1 mM inhibited AFC by 75% and 34% in WT and m/m mice, respectively, whereas a higher concentration (5 mM) induced a 75% inhibition of AFC in both groups. The beta2-agonist terbutaline significantly increased AFC in WT but not in m/m mice. These results show that despite the compensatory increase in alpha- and gamma-ENaC protein expression observed in mutant mouse lung, low expression of beta-ENaC results in a moderate impairment of baseline AFC and in decreased AFC sensitivity to amiloride, suggesting a possible change in the stoichiometry of ENaC channels. Finally, adequate beta-ENaC expression appears to be required for AFC stimulation by beta2-agonists.
Randrianarison
Nadia
N
INSERM U773, CRB3, Université Denis Diderot-Paris 7, 16 rue Henri Huchard, 75018 Paris, France.
Clerici
Christine
C
Ferreira
Chrystophe
C
Fontayne
Alexandre
A
Pradervand
Sylvain
S
Fowler-Jaeger
Nicole
N
Hummler
Edith
E
Rossier
Bernard C
BC
Planès
Carole
C
D000818:Animals; D053503:Epithelial Sodium Channels / Q000096:biosynthesis*; D015633:Extravascular Lung Water / Q000378:metabolism*; D015870:Gene Expression; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D021122:Protein Subunits / Q000096:biosynthesis; D011650:Pulmonary Alveoli / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D013726:Terbutaline / Q000494:pharmacology
D053503:Epithelial Sodium Channels; D021122:Protein Subunits; D012333:RNA, Messenger; C507049:Scnn1b protein, mouse; D013726:Terbutaline