Effects of inactivity on myosin heavy chain composition and size of rat soleus fibers

• Published in: Muscle & nerve Vol. 21; no. 3; pp. 375 - 389
• Main Authors: Grossman, Elena J., Roy, Roland R., Talmadge, Robert J., Zhong, Hui, Edgerton, V. Reggie
• Format: Journal Article
• Language: English
• Published: New York John Wiley & Sons, Inc 01.03.1998; Wiley
• Subjects: Animals; Atrophy; Biological and medical sciences; Cats; Female; fiber cross-sectional area; fiber type composition; Fundamental and applied biological sciences. Psychology; Immobilization - physiology; Life Sciences (General); Muscle Fibers, Skeletal - pathology; Muscle Fibers, Skeletal - physiology; Muscle, Skeletal - anatomy & histology; Muscle, Skeletal - innervation; Muscle, Skeletal - physiology; Myosin Heavy Chains - chemistry; Myosin Heavy Chains - metabolism; neuromuscular activity; Rats; Rats, Sprague-Dawley; Space life sciences; Species Specificity; Spinal Cord - physiology; spinal cord isolation; Spinal Nerve Roots - physiology; Striated muscle. Tendons; Vertebrates: osteoarticular system, musculoskeletal system; Non-Nasa Center; Nasa Discipline Musculoskeletal; Composition; Spinal cord; Rat; Motor pathway; Rodentia; Central nervous system; Muscular fiber type I; Striated muscle; Muscular fiber type II; Soleus muscle; Atrophy; Vertebrata; Mammalia; Morphology; Deafferentation; NASA Discipline Musculoskeletal; Non-NASA Center
• ISSN: 0148-639X; 1097-4598
• DOI: 10.1002/(SICI)1097-4598(199803)21:3<375::AID-MUS12>3.0.CO;2-Z

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.