Effects of inactivity on myosin heavy chain composition and size of rat soleus fibers.
Myosin heavy chain (MHC) and fiber size properties of the adult rat soleus were determined after 4-60 days of complete inactivity, i.e., lumbar spinal cord isolation. Soleus atrophy was rapid and progressive, i.e., 25% and 64% decrease in weight and 33% and 75% decrease in fiber size after 4 and 60 days of inactivity, respectively. Changes in MHC occurred at a slower rate than the atrophic response. After 15 days there was de novo expression of type IIx MHC (approximately 10%). By 60 days, type IIx MHC accounted for 33% of the total MHC content, and 7% of the fibers contained only type IIx MHC. The relative amount of type I MHC was reduced from 93% in control to 49% after 60 days of inactivity. Therefore, the effects of 60 days of inactivity suggest that during this time period at least 75% of fiber size and approximately 40% of type I MHC composition of the adult rat soleus can be attributed to activation-related events.
Grossman
E J
EJ
Department of Physiological Science, University of California, Los Angeles 90095, USA.
Roy
R R
RR
Talmadge
R J
RJ
Zhong
H
H
Edgerton
V R
VR
D000818:Animals; D001284:Atrophy; D002415:Cats; D005260:Female; D007103:Immobilization / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000473:pathology / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000294:innervation / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013045:Species Specificity; D013116:Spinal Cord / Q000502:physiology*; D013126:Spinal Nerve Roots / Q000502:physiology
D018995:Myosin Heavy Chains