title: Effects of inactivity on myosin heavy chain composition and size of rat soleus fibers.
abstract: 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.
authors.affiliation: Department of Physiological Science, University of California, Los Angeles 90095, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Grossman
authors.forename: R R
authors.initials: RR
authors.lastname: Roy
authors.forename: R J
authors.initials: RJ
authors.lastname: Talmadge
authors.forename: H
authors.initials: H
authors.lastname: Zhong
authors.forename: V R
authors.initials: VR
authors.lastname: Edgerton
mesh_terms: 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
chemical_list: D018995:Myosin Heavy Chains