Developmental differences in rabbit lung epithelial cell Na(+)-K(+)-ATPase.

Previous studies showed that ouabain-sensitive rubidium (86Rb+) uptake by rabbit lung epithelial cells increases at birth, followed by a more gradual postnatal increase, reaching adult values by age 30 days. To see whether these changes in ouabain-sensitive cation transport were the result of changes in Na+ pump number or turnover rate, we measured binding of [3H]ouabain and ouabain-sensitive 86Rb+ uptake by freshly isolated lung epithelial cells harvested from near-term fetal, newborn, and adult rabbits. Ouabain-sensitive 86Rb+ uptake by fetal cells was 1/4 that of newborn cells and 1/10 that of adult cells. The maximal number of ouabain binding sites (Umax) was the same for fetal and newborn cells but almost threefold greater for adult cells. Na+ pump turnover rate, determined from ouabain-sensitive 86Rb+ uptake and Umax, was four times greater in newborn and adult cells than it was in fetal cells. Thus the increase in 86Rb+ uptake at birth could be explained by an increase in Na(+)-K(+)-adenosinetriphosphatase (ATPase) turnover rate, whereas the postnatal increase in 86Rb+ uptake could be accounted for by an increase in the amount of Na(+)-K(+)-ATPase per cell.