Cp. Ingalls et al., DISSOCIATION OF FORCE PRODUCTION FROM MHC AND ACTIN CONTENTS IN MUSCLES INJURED BY ECCENTRIC CONTRACTIONS, Journal of muscle research and cell motility, 19(3), 1998, pp. 215-224
The primary purpose of this study was to determine the relationship be
tween myosin heavy chain (MHC) and actin contents and maximum isometri
c tetanic force (P-o) in mouse extensor digitorum longus (EDL) muscles
following eccentric contraction-induced injury. P-o and protein conte
nts were measured in injured (n = 80) and contralateral control (n = 8
0) EDL muscles at the following time points after in vivo injury: sham
, 0, 0.25, 1, 3, 5, 14, and 28 days. P-o was reduced by 37 +/- 2.3% to
49 +/- 3.8% (p less than or equal to 0.05), while MHC and actin conte
nts were unaltered from 0 to 3 days after injury. Whereas P-o partiall
y recovered between 3 and 5 days (from -49 +/- 3.8% to -35 +/- 3.6%),
MHC and actin contents in the injured muscles declined by 19 +/- 4.9%
and 20 +/- 5.3%, respectively, by 5 days compared with control muscles
. Decrements in P-o were similar to the reductions in MHC and actin co
ntents at 14 (similar to 24%) and 28 (similar to 11%) days. Evaluation
of myofibrillar and soluble protein fractions indicated significant r
eductions in the content of major proteins at 5 and 14 days. Immunoblo
ts of heat shock protein 72 revealed elevations starting at 0.25 days,
peaking during 1-3 days, and declining after 5 days. These findings i
ndicate that decreased contractile protein content is not related to t
he initial decrease in P-o. However, decreased MHC and actin contents
could account for 58% of the P-o reduction at 5 days, and for nearly a
ll the decrements in P-o from 14 to 28 days. (C) Chapman & Hall Ltd.