Mechanical regulation of cardiac myocyte protein turnover and
myofibrillar structure .
Simpson, D. G., W. W. Sharp, T. K. Borg, R. L. Price, L. Terracio, and
A. M. Samarel.
Department of Developmental Biology and Anatomy, University of
South Carolina School of Medicine, Columbia, SC. 29208 and
Departments of Medicine and Physiology, Loyola University Chicago
Stritch School of Medicine, Maywood, IL. 60153
APStracts 2:0364C, 1995.
Mechanical forces play an essential role in regulating the synthesis
and assembly of contractile proteins into the sarcomeres of cardiac
myocytes. To examine if physical forces might also regulate the
turnover of contractile proteins at a post-translational site of
control, beating and non-beating neonatal cardiac myocytes (NCM) were
subjected to a 5 % static stretch. The L-type calcium channel blocker
nifedipine (12 [lambda]M) was used to inhibit contraction. Pulse
-chase biosynthetic labeling experiments demonstrated that contractile
arrest accelerated the loss of isotopic tracer from the total
myofibrillar protein fraction, myosin heavy chain (MHC) and actin,
but not desmin. Myofibrillar abnormalities developed in parallel with
these metabolic changes. A 5 % static load appeared to partially
stabilize myofibrillar structure in non-beating NCM and suppressed
the loss of isotopic tracer from the total myofibrillar protein
fraction, MHC, and actin in beating and non-beating NCM. Contractile
activity and/or a static stretch promoted the accumulation of MHC,
actin and desmin. Applying a static load to myocytes that lacked pre
-existing myofibrils did not promote the assembly of sarcomeres or
alter protein turnover. These data indicate that the turnover of MHC
and actin is correlated with the organizational state of the
myofibrillar apparatus.
Received 25 July 1995; accepted in final form 2 October 1995.
APS Manuscript Number C455-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95