The role of alpha-, beta-, and gamma-ENaC subunits in distal lung epithelial fluid absorption induced by pulmonary edema fluid.
Edema fluid (EF) increases epithelial Na(+) transport by rat fetal distal lung epithelia (FDLE) and induces net lung fluid absorption in fetal mouse lung explants [Rafii B, Gillie DJ, Sulowski C, Hannam V, Cheung T, Otulakowski G, Barker PM, O'Brodovich H. J Physiol (Lond) 544: 537-548, 2002]. We now show that EF increases fluid absorption across monolayers of rat FDLE in a dose-dependent manner. To study the role of subunits of the epithelial Na(+) channel (ENaC) in the phenomena, we cultured explants from the distal lungs of 16-day gestational age wild-type (WT) or alpha-, beta-, or gamma-ENaC knockout or heterozygote (HT) mice. WT explants cultured in media continuously expanded over time as a result of net fluid secretion. In contrast, when explants were exposed to EF for 24 h, net fluid absorption occurred. EF-exposed explants had normal histology, but marked changes were seen after Triton X-100 or staurosporine exposure. Transmission electron microscopy showed EF promoted lamellar body formation and abundant surfactant in the explants' lumens. EF-induced changes in explant size were similar in alpha-ENaC knockout, WT, and HT littermate fetal lung explants (P > 0.05). In contrast, EF's effect was attenuated in beta- and gamma-ENaC knockouts (P < 0.05) vs. WT and HT littermate fetal lung explants. EF exposure slightly decreased or had no effect on mRNA levels for alpha-ENaC in various mouse genotypes but decreased expression of beta- and gamma-ENaC subunit mRNAs (P < 0.01) across all genotype groups. We conclude that beta- and gamma-, but not alpha-, ENaC subunits are essential for EF to exert its maximal effect on net fluid absorption by distal lung epithelia.
Elias
Nael
N
Program in Lung Biology, Hospital for Sick Children Research Institute, Toronto, canada.
Rafii
Bijan
B
Rahman
Muhammad
M
Otulakowski
Gail
G
Cutz
Ernest
E
O'Brodovich
Hugh
H
D000042:Absorption / Q000187:drug effects; D000818:Animals; D004247:DNA / Q000096:biosynthesis; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D015633:Extravascular Lung Water / Q000378:metabolism*; D005333:Fetus / Q000187:drug effects / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D005865:Gestational Age; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D008168:Lung / Q000187:drug effects / Q000473:pathology* / Q000648:ultrastructure; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017830:Octoxynol / Q000494:pharmacology; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D011654:Pulmonary Edema / Q000473:pathology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology
D053503:Epithelial Sodium Channels; D021122:Protein Subunits; D012333:RNA, Messenger; D017830:Octoxynol; D004247:DNA; D019311:Staurosporine