Creatine kinase in developing skeletal and cardiac muscle of the rat

Abstract

This paper reports the changes in specific activity and isoenzyme pattern of creatine kinase in skeletal and cardiac muscle of Holtzman rats during development. There is a rapid accumulation of enzyme after day 17 of gestation and, starting at a slightly earlier time, a transition from “brain” to “heart” and then to predominantly “muscle” isoenzyme takes place. Although the changes are similar in the two types of muscle, important differences are found. The specific activity of creatine kinase is much lower in developing and mature cardiac muscle, but adult levels of the enzyme are approximated sooner in cardiac than in skeletal muscle tissue. The changes in isoenzymes are more gradual and less profound in cardiac muscle than in skeletal muscle. The factors which may relate to these striking changes in creatine kinase are discussed.