Independent expression of cardiac type I and II cyclic AMP-dependent protein kinase during murine embryogenesis and postnatal development.

The amount of total cyclic AMP-dependent protein kinase and of the protein kinase isozymes present in mouse heart changes during development. During embryogenesis, the total cardiac protein kinase activity increases most markedly during the 6 days prior to birth. A maximum kinase level is achieved in the 7 day-old neonate, and then activity progressively declines to an adult level approximating that of the mid-embryo. The type II kinase exhibits a moderate increase during late embryogenesis which declines by the time of birth. The type I isozyme increases throughout embryogenesis and the first neonatal week to a maximum specific activity five-fold higher than the mid-embryogenesis level. The isozyme level then falls to an adult activity similar to the mid-embryonic. These changes in isozyme profile are reflected in a changing type I to type II kinase ratio of 1.1 at 13--14 days embryogenesis, 2.4 at birth, 3.0 in the 7 day-old neonates, and 1 in the adult heart. Thus, the two protein kinase isozymes change in association with the developmental process in an independent fashion.