title: Enhancement of alveolar epithelial sodium channel activity with decreased cystic fibrosis transmembrane conductance regulator expression in mouse lung.
abstract: We sought to establish whether the cystic fibrosis transmembrane conductance regulator (CFTR) regulates the activity of amiloride-sensitive sodium channels (ENaC) in alveolar epithelial cells of wild-type, heterozygous (Cftr(+/-)), knockout (Cftr(-/-)), and ΔF508-expressing mice in situ. RT-PCR studies confirmed the presence of CFTR message in freshly isolated alveolar type II (ATII) cells from wild-type mice. We patched alveolar type I (ATI) and ATII cells in freshly prepared lung slices from these mice and demonstrated the presence of 4-pS ENaC channels with the following basal open probabilities (P(o)): wild-type=0.21 ± 0.015: Cftr(+/-)=0.4 ± 0.03; ΔF508=0.55 ± 0.01; and Cftr(-/-)=and 0.81 ± 0.016 (means ± SE; n ≥ 9). Forskolin (5 μM) or trypsin (2 μM), applied in the pipette solution, increased the P(o) and number of channels in ATII cells of wild-type, Cftr(+/-), and ΔF508, but not in Cftr(-/-) mice, suggesting that the latter were maximally activated. Western blot analysis showed that lungs of all groups of mice had similar levels of α-ENaC; however, lungs of Cftr(+/-) and Cftr(-/-) mice had significantly higher levels of an α-ENaC proteolytic fragment (65 kDa) that is associated with active ENaC channels. Our results indicate that ENaC activity is inversely correlated to predicted CFTR levels and that CFTR heterozygous and homozygous mice have higher levels of proteolytically processed ENaC fragments in their lungs. This is the first demonstration of functional ENaC-CFTR interactions in alveolar epithelial cells in situ.
authors: Department of Anesthesiology, School of Medicine, University of Alabama at Birmingham, 35205-3703, USA.
authors: Ahmed
authors: A
authors: Lazrak
authors: Asta
authors: A
authors: Jurkuvenaite
authors: Lan
authors: L
authors: Chen
authors: Kim M
authors: KM
authors: Keeling
authors: James F
authors: JF
authors: Collawn
authors: David M
authors: DM
authors: Bedwell
authors: Sadis
authors: S
authors: Matalon
mesh_terms: D056809:Alveolar Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects; D006579:Heterozygote; D006720:Homozygote; D008564:Membrane Potentials / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D009865:Oocytes; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*; D014357:Trypsin / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D053503:Epithelial Sodium Channels; D010446:Peptide Fragments; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D000584:Amiloride; D014357:Trypsin