Effect of developmental age and hyperoxia exposure on kinase and phosphatase activities in newborn rat lungs

To better understand the biochemical events accompanying lung alveolarization and development, we studied the specific activity of the cAMP-dependent protein kinase (PKA) and the type 2A protein phosphastase (PP2A), and the activity and protein content of the calcium- and lipid-dependent protein kinase (PKC) in cytosolic preparations of lungs. Lungs were obtained from rat pups on day 2 of life and on days 7, 14, and 27 from pups exposed to hyperoxia (> 95% O2, days 4-14; 65% O2 days 15-27) or normoxia from day 4 onwards. There were no significant changes in PKA specific activity with developmental age or hyperoxic exposure. PKC specific activity increased significantly (P < .05) in normoxic animals from day 2 (64 +/- 13.5 pmol phosphate released/min/mg protein) to day 14 (105 +/- 9). The increase was sustained to day 27. There was no effect on PKC activity due to hyperoxia alone (ANOVA). This increase in PKC activity was accompanied by an increase in the mass of the delta, epsilon and zeta isoforms of PKC in normoxic pups. The gamma isoform of PKC was undetectable in all samples whereas the alpha and beta isoforms were detectable but showed no changes with developmental age. PP2A specific activity increased significantly (P < .05) from 13.3 +/- 0.5 nmol phosphate released/min/mg protein on day 2 to 17.7 +/- 0.9 on day 7 in normoxic pups, then returned to day 2 level at advanced developmental age. Hyperoxia exposure prevented the increase in enzyme activity observed on day 7 in normoxic animals. These data suggest that protein phosphorylation may be one mechanism by which alveolarization is regulated in developing lungs.