Epithelial Na 1 Channel (ENaC) Expression in the Developing Normal and Abnormal Human Perinatal Lung

1 channel (ENaC) activity at the time of birth results in respiratory distress. To investigate potential mech- anisms, the ontogeny and cellular distribution of the a ENaC sub- unit mRNA expression was studied in normal, immature, and ab- normal (hypoplastic) human fetal lungs using nonradioisotopic in situ hybridization. Surprisingly, a ENaC expression was detected at the embryonic stage of normal lung development (4 to 5 wk ges- tation) when expression was localized to the fetal lung bud epi- thelium. By late gestation, ENaC was expressed in the conductive and respiratory airway epithelium, serous cells, and the distal lung unit in an alveolar type II (ATII) epitheliumlike distribution. Signifi- cant a ENaC expression was found in newborn lung diseases asso- ciated with respiratory distress. One explanation is that a ENaC mRNA is constitutively expressed, and that activity is regulated, at least in part, at the post-transcriptional level. Alternative explana- tions are that the expression of the b or g ENaC subunits may be impaired in certain newborn lung diseases or that alternate Na 1