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1 Department of Biological Sciences, California State Polytechnic University, Pomona 91768; 2 Brain Research Institute, University of California, Los Angeles 90095; 3 Department of Physiology and Biophysics and Department of Orthopaedics, College of Medicine, University of California, Irvine 92717; and 4 Physiological Science Department, University of California, Los Angeles, California 90095
The effects of a complete spinal cord transection (ST) on the mechanical properties of the rat soleus were assessed 3 and 6 mo post-ST and compared with age-matched controls. Maximal tetanic force was reduced by ~44 and ~25% at 3 and 6 mo post-ST, respectively. Similarly, maximum twitch force was reduced by ~29% in 3-mo and ~17% in 6-mo ST rats. ST resulted in faster twitch properties as evidenced by shorter time to peak tension (~45%) and half-relaxation time (~55%) at both time points. Maximum shortening velocity was significantly increased in ST rats whether measured by extrapolation from the force-velocity curve (approximately twofold at both time points) or by slack-test measurements (over twofold at both time points). A significant reduction in fatigue resistance of the soleus was observed at 3 (~25%) and 6 mo (~45%) post-ST. For the majority of the speed-related properties, no significant differences were detected between 3- and 6-mo ST rats. However, the fatigue resistance of the soleus was significantly lower in 6- vs. 3-mo ST rats. These data suggest that, between 3 and 6 mo post-ST, force-related properties tended to recover, speed-related properties plateaued, and fatigue-related properties continued to decline. Thus some specific functional properties of the rat soleus related to contractile force, speed, and fatigue adapted independently after ST.
adaptation; contractile function; fatigue; myosin heavy chain; paralysis; plasticity
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