O2-induced ENaC expression is associated with NF-kappaB activation and blocked by superoxide scavenger.
Cultured rat fetal distal lung epithelial cells (FDLEs), when switched from fetal (3%) to postnatal (21%) O2 concentrations, have increased epithelial Na+ channel (ENaC) mRNA levels and amiloride-sensitive Na+ transport [O. Pitkänen, A. K. Tanswell, G. Downey, and H. O'Brodovich. Am. J. Physiol. 270 (Lung Cell. Mol. Physiol. 14): L1060-L1066, 1996]. The mechanisms by which O2 mediates these effects are unknown. After isolation, FDLEs were kept at 3% O2 overnight, then switched to 21% O2 (3-21% O2 group) or maintained at 3% O2 (3-3% O2 group) for 48 h. The amiloride-sensitive short-circuit current (Isc) in the 3-21% O2 group was double that in the 3-3% O2 group. Amiloride-sensitive Isc could not be induced by medium conditioned by 21% O2-exposed FDLEs but was reversed by returning the cells to 3% O2. Neither the cyclooxygenase inhibitor ibuprofen, liposome-encapsulated catalase, nor hydroperoxide scavengers (U-74389G or Trolox) blocked the O2-induced amiloride-sensitive Isc. In contrast, the cell-permeable superoxide scavenger tetramethylpiperidine-N-oxyl (TEMPO) eliminated the O2-induced increases in amiloride-sensitive Isc and ENaC mRNA levels. The switch from 3 to 21% O2 induced the transcription factor nuclear factor-kappaB, which could also be blocked by TEMPO. We conclude that 1) the O2-induced increase in amiloride-sensitive Isc is reversible and 2) the O2-induced increase in amiloride-sensitive Isc and ENaC mRNA levels is associated with activation of nuclear factor-kappaB and may be mediated, at least in part, by superoxide.
Rafii
B
B
Medical Research Council Group in Lung Development, Hospital for Sick Children Research Institute and Department of Paediatrics, University of Toronto, Toronto, Ontario, Canada M5G 1X8.
Tanswell
A K
AK
Otulakowski
G
G
Pitkänen
O
O
Belcastro-Taylor
R
R
O'Brodovich
H
H
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002478:Cells, Cultured; D016384:Consensus Sequence; D004622:Embryo, Mammalian; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D016166:Free Radical Scavengers / Q000494:pharmacology; D005786:Gene Expression Regulation; D018496:Hyperoxia; D008168:Lung / Q000166:cytology / Q000502:physiology*; D016328:NF-kappa B / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides; D010100:Oxygen / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000096:biosynthesis / Q000235:genetics*; D013481:Superoxides / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000378:metabolism
D016166:Free Radical Scavengers; D016328:NF-kappa B; D009838:Oligodeoxyribonucleotides; D015222:Sodium Channels; D018808:Transcription Factor AP-1; D013481:Superoxides; D000584:Amiloride; D010100:Oxygen