AJP - Heart and Circulatory Physiology, Vol 249, Issue 2 344-H350, Copyright © 1985 by American Physiological Society
Myocyte and nonmyocyte RNA polymerase activity and chromatin template function
P. B. Taylor and Q. Tang
Myocardial and nonmyocardial cell nuclei were isolated from ventricles of
adult male Wistar rats by means of sucrose density centrifugation. RNA
polymerase activity in myocyte nuclei was approximately 80-90% higher than
in nonmyocytes. Total myocyte chromatin template activity using Escherichia
coli RNA polymerase was linear and about onefold greater than the
nonmyocyte fraction over a fivefold range of chromatin concentrations.
Preincubation time required for RNA polymerase to form a stable binding
complex with chromatin was at least 40 min for myocyte and 30 min for
nonmyocyte nuclear subsets. Titration of chromatin against a fixed amount
of RNA polymerase (5 micrograms) showed that 5 micrograms of myocyte
chromatin (as DNA) and 8 micrograms of nonmyocyte chromatin (as DNA),
respectively, were required to saturate the enzyme. These results indicate
that myocyte chromatin can support greater enzyme binding than can
nonmyocyte chromatin. The distribution of DNA fragments from isolated
myocyte and nonmyocyte nuclei were similar when alkaline sucrose density
centrifugation was used. Chromatin prepared from these nuclear subsets
showed no difference in degree of DNA fragmentation. These observations
indicate that compared with nonmuscle cells, myocytes from adult rat hearts
have higher RNA polymerase activity, greater overall chromatin template
function, and higher binding capacity for RNA polymerase. Collectively,
these data suggest that adult cardiac muscle cells should have a larger
potential for RNA synthesis than nonmuscle cells.
