Effects of hind limb unweighting on the expression of physiological markers of muscle atrophy and myofibrillar protein content in the soleus and extensor digitorum longus of Sprague-Dawley rats.

The purpose of this study was to determine the effects of hind limb unweighting on the expression of physiological markers of muscle atrophy and myofibrillar protein content in the soleus (SOL) and extensor digitorum longus (EDL) of Sprague-Dawley rats. After the 2-week unweighting period, the rats (4 HU; 4 months old, 4 CON; 5 months old) were euthanized, EDL and SOL excised and sent to the Exercise and Biochemical Nutrition Laboratory at Baylor University. The samples were analyzed for myofibrillar protein content, MHC isoform mRNA expression, calpain1, 2 activities, and ubiquitin proteolytic enzymes E2, E3, Atrogin-1, RF-1. In HU a reduction in myofibrillar content was witnessed (49% SOL, 81% EDL). A significant main effect for group was observed (p = 0.047) indicating HU produced a significant reduction in myofibrillar protein content and changes in MHC mRNA expression. Calpain 1, 2 mRNA expression in HU EDL increased with significant interactions (p = 0.003) for calpain 1 mRNA. E3 mRNA witnessed a significant interaction (p = 0.037), and E2, atrogin-1, and RF-1, displayed no significant interactions (p > 0.05).