Influence of suspension hypokinesia on rat soleus muscle.
Hindlimb hypokinesia was induced in rats by the Morey method to characterize the response of the soleus muscle. Rats suspended for 1-4 wk exhibited continuous and significant declines in soleus mass, function, and contractile duration. Soleus speeding was in part explained by an alteration in fiber type. The normal incidence of 70-90% type I fibers in the soleus muscle was reduced after 4 wk of suspension to 50% or less in 9 of 11 rats. A significant decline in type I myosin isozyme content occurred without a change in that of type II. Other observed histochemical changes were characteristic of denervation. Consistent with soleus atrophy, there was a significant increase in lysosomal (acid) protease activity. One week of recovery after a 2-wk suspension was characterized by a return to values not significantly different from control for muscle wet weights, peak contraction force, one-half relaxation time, and type I myosin. Persistent differences from control were observed in maximal rate of tension development, contraction time, and denervation-like changes.
D000818:Animals; D016282:Aspartic Acid Endopeptidases; D001284:Atrophy / Q000473:pathology; D010450:Endopeptidases / Q000378:metabolism; D006614:Hindlimb; D007103:Immobilization; D007527:Isoenzymes; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000201:enzymology / Q000473:pathology / Q000502:physiology*; D009218:Myosins / Q000032:analysis; D051381:Rats; D011919:Rats, Inbred Strains
D007527:Isoenzymes; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; D009218:Myosins