Mrf4, myf-5 and myogenin mrnas in the adaptive responses of mature rat
muscle.
Jacobs-El, Jamil, Ming-Yuan Zhou, and Brenda Russell.
Department of Physiology and Biophysics, University of Illinois College of
Medicine, Chicago, Illinois 60612
APStracts 2:0016C, 1995.
We studied the possible role of specific muscle regulatory factors (MRFs) in
the adaptive response to changes in contractile activity in mature skeletal
muscle. The tibialis anterior muscle of anesthetized female rats was
subjected to low-frequency stimulation, static stretch, or a combination of
both. Message levels of MRFs were observed after 2 hours of activity and the
subsequent 20 hour recovery period by slot blot and in situ hybridizations for
MRF4, Myf-5 and myogenin. A combination of stimulation and stretch for 2 hours
increased MRF4 (11.6 + 5.3 fold) and Myf-5 (6.6 + 1.4 fold). In situ
hybridization showed abundance in some regions of the muscle with positive
staining near peripheral nuclei of both large and small fibers. Message
levels remained high for 30 minutes and declined to near control levels by 20
hours of recovery. Myogenin mRNA levels were unaffected by any manipulations.
Neither stretch alone, nor 10 Hz electrical stimulation alone, induces a
significant increase in MRFs. We conclude that myonuclei, and possibly
activated myoblasts, increase expression of Myf-5 and MRF4 after a combination
of both stimulation and stretch for 2 hours.
Received 11 July 1994; accepted in final form 27 October 1994
APS Manuscript Number C0393-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1994 The American Physiological Society.
Published in APStracts on 27 February 1995.