Myocardial nuclear protein kinases during postnatal development

Abstract

Chromatin template activity of isolated rat myocardial cells declines progressively during the first few weeks of postnatal life, a time period also characterized by restriction in myocardial proliferative capacity. Multiple protein kinases have been isolated from the nuclei of myocardial cells. Protein kinase activity decreased progressively during the first 3 wk of postnatal development, mostly in two fractions (III and V). Cyclic AMP dependency, substrate specificity, and phosphorylation patterns of endogenous substrates did not change appreciably with age. Higher phosphorylating activity of protein kinases from younger rats correlated with increased capacity to enhance myocardial RNA synthesis in vitro. This suggests the possibility that the decrease in chromatin template activity with age may be, in part, related to the decline in nuclear phosphokinase activities.