Changes in skeletal muscle properties following hindlimb suspension

Changes in AChE regulation, the functions of the sarcoplasmic reticulum (SR), and muscle fiber-type population in the extensor digitorium longus (EDL) and soleus of male rats suspended in a nonweight-bearing position are studied. Muscle weight, AChE activity, protein content, SR calcium loading rates, and muscle types in the suspended and control rats are evaluated and compared. It is observed that following 1-4 weeks of suspension the EDL is unaffected; however, the soleus muscle weight, and protein content decrease and the AChE activity increases. The SR calcium loading rates of EDL decrease 10 percent and the soleus increase 50 percent in the suspended rats. The data reveal that the population of muscle type 1 (slow fibers) decreases and type 2 (fast fibers) increases for the soleus, and the distribution is unchanged for the EDL of the suspended rats. It is detected that a nonweight-bearing position affects the soleus (a fast-twitch muscle), but not the EDL (a slow-twitch muscle).