Muscle and non-muscle cell RNA polymerase activity during the development of myocardial hypertrophy

It is demonstrated that changes do occur in either the activity or amount of RNA polymerase enzymes in cardiac muscle and non-muscle cells during the development of hypertrophy, however, the delay in the onset of these changes and the lack of enhancement ofRNA polymerase I in non-Muscle cells suggest that other regulatory mechanism, such as, chromatin template activity, may also be present.

Abstract

Abstract RNA polymerase activity was measured in separated cardiac muscle and non-muscle cell nuclei during the development of acute pressure overload induced myocardial hypertrophy in the rat. Varying concentrations of α-amanitin were used to measure changes in the three major classes of RNA polymerases. Total RNA polymerase activity in both muscle and non-muscle cells began to increase above sham-operative levels by 48 h after aortic constriction, reaching maximal stimulation 72 h after surgery. A similar increase in both cell populations was found in the presence of low concentrations of α-amanitin. In the presence of 1 μg/ml of α-amanitin muscle cell RNA polymerase increased as above but non-muscle cell polymerase remained unchanged. Changes at 72 h after aortic constriction in the activities of RNA polymerase I, II and III were calculated from these data. RNA polymerases II and III increased two-fold in both muscle and non-muscle nuclei. RNA polymerase I activity showed a five-fold increase in muscle nuclei but was unchanged in non-muscle nuclei. These data demonstrate that changes do occur in either the activity or amount of RNA polymerase enzymes in cardiac muscle and non-muscle cells during the development of hypertrophy. However, the delay in the onset of these changes and the lack of enhancement of RNA polymerase I in non-muscle cells suggest that other regulatory mechanism, such as, chromatin template activity, may also be present.