AJP - Heart and Circulatory Physiology, Vol 240, Issue 6 901-H907, Copyright © 1981 by American Physiological Society
Muscle and nonmuscle cell RNA polymerase activities in early myocardial hypertrophy
A. F. Cutilletta
RNA polymerase was solubilized from separated rat cardiac muscle and
nonmuscle cells during the development of myocardial hypertrophy 1 or 3
days after sham operation or aortic constriction. Six fractions of enzymes
designated IA, IB, IIA, IIB, IIIA, and IIIB were identified by
DEAE-Sephadex chromatography in each cell population. Fractions designated
IA and IB, IIA and IIB, and IIIA and IIIB were similar to RNA polymerase I,
II, and III, respectively, found in other eukaryotes. Muscle cell enzyme
activity from sham-operated and aortic-constricted rats did not
significantly differ 1 day after intervention. By 3 days there was a
significant increase in the activity of each enzyme fraction in muscle
cells from aortic-constricted rats. There was a slight increase in IIA
activity in nonmuscle cells from aortic-constricted rats at 1 day. By 3
days after aortic constriction RNA polymerase IIA, IIB, and IIIB activities
increased in nonmuscle cells, but no change was noted in nonmuscle RNA
polymerase IA, IB, and IIIA. Changes in RNA polymerase activities in
cardiac muscle and nonmuscle cells occur during the development of
myocardial hypertrophy but do not appear to correlate with reported changes
in RNA synthesis. chromatin-template activity, however, did increase in
cardiac muscle cells at both 1 and 3 days after aortic constriction. A
similar increase was not seen in nonmuscle cell chromatin-template activity
until 3 days. These data suggest that the initial increase in RNA synthesis
during the development of myocardial hypertrophy is related to changes in
chromatin-template activity in muscle cells. The activities of the RNA
polymerase increase after a short delay and vary in their response.
