Early expression of beta- and gamma-subunits of epithelial sodium channel during human airway development

The amiloride-sensitive epithelial Na+ channel (ENaC) is an apical membrane protein complex involved in active Na+ absorption and in control of fluid composition in airways. There are no data reporting the distribution of its pore-forming alpha-, beta-, and gamma-subunits in the developing human lun g. With use of two different rabbit polyclonal antisera raised against beta - and gamma-ENaC, immunohistochemical localization of the channel was perfo rmed in fetal (10-35 wk) and in adult human airways. Both subunits were det ected after 17 wk of gestation on the apical domain of bronchial ciliated c ells, in glandular ducts, and in bronchiolar ciliated and Clara cells. Afte r 30 wk, the distribution of beta- and gamma-subunits was similar in fetal and adult airways. In large airways, the two subunits were detected in cili ated cells, in cells lining glandular ducts, and in the serous gland cells. In the distal bronchioles, beta- and gamma-subunits were identified in cil iated and Clara cells. Ultrastructural immunogold labeling confirmed the id entification of beta- and gamma-ENaC proteins in submucosal serous cells an d bronchiolar Clara cells. Early expression of ENaC proteins in human fetal airways suggests that Na+ absorption might begin significantly before birt h, even if secretion is still dominant.