Developmentally regulated expression of cytochrome-coxidase isoforms in regenerating rat skeletal muscle

The developmental expression of tissue-specific isoforms of cytochrome-c oxidase (COX) subunit VIII [heart (COX VIII-H) and liver (COX VIII-L)] and the influence of innervation were examined in regenerating fast [extensor digitorum longus (EDL)] and slow (soleus) muscles. In adult muscles, COX VIII-H was the predominant isoform. The COX VIII-L mRNA was expressed 3 days after induction of regeneration, and it progressively decreased after 7, 10, 14, and 30 days of regeneration in both muscles. In contrast, the expression of COX VIII-H mRNA accumulated as myogenesis proceeded to the myotube stage between 7 and 10 days of regeneration and progressively increased to near control levels by 30 days. The influence of innervation on the expression of COX VIII and alpha-actin isoforms was examined in control, innervated, and denervated regenerating muscles at 3 and 10 days. The relative expression of COX VIII-L mRNA in denervated regenerating EDL muscles was significantly greater, while that of COX VIII-H was significantly less than in innervated regenerating EDL muscles after 10 days of regeneration. Similarly, cardiac alpha-actin mRNA levels were elevated in denervated regenerating EDL muscles after 10 days of regeneration. In conclusion, motor innervation influences the transition from the COX VIII-L to COX VIII-H isoform during myogenesis in regenerating muscles.