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

✍ Scribed by Elena J. Grossman; Roland R. Roy; Robert J. Talmadge; Hui Zhong; V. Reggie Edgerton

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 866 KB
• Volume: 21
• Category: Article
• ISSN: 0148-639X
• DOI: 10.1002/(sici)1097-4598(199803)21:3<375::aid-mus12>3.0.co;2-z

✦ Synopsis

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.