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1 Department of Physiology, St. Marianna University School of Medicine, Miyamae, Kawasaki City, Kanagawa 216-8511; 2 School of Health and Sport Sciences, Osaka University, Osaka 560-0043; and 3 Aomori University of Health and Welfare, Aomori 030-8505, Japan
Responses of the properties of
connectin molecules in the slow-twitch soleus (Sol) and fast-twitch
extensor digitorum longus muscles of rats to 3 days of unloading with
or without 3-day reloading were investigated. The wet weight (relative
to body wt) of Sol, not of extensor digitorum longus, in the unloaded
group was significantly less than in the age-matched control
(P < 0.05). Immunoelectron microscopic analyses showed
that a monoclonal antibody against connectin (SM1) bound to the I-band
region close to the edge of the A band at resting length and moved
reversibly away from the Z line as the muscle fibers were stretched. In
Sol, the displacement of the SM1-bound dense spots in response to
stretching decreased after hindlimb suspension. There were no changes
in the molecular weights and the percent distributions of
- and
-connectin in both muscles after hindlimb suspension. A significant
increment of percent
-connectin in Sol was observed after 3 days of
reloading after hindlimb suspension (P < 0.05). It is
suggested that the elasticity of connectin filaments in the I-band
region of the atrophied Sol fibers was reduced relative to that of the
control fibers. The lack of the elasticity in atrophied muscle fibers may cause a decrease in contractile function.
fast and slow muscles of rat; hindlimb suspension
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