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

The developmentalexpression of tissue-specific isoforms ofcytochrome-c oxidase(COX) subunit VIII heart (COX VIII-H) and liver (COXVIII-L)] and the influence of innervation were examined inregenerating fast extensor digitorum longus (EDL)] andslow (soleus) muscles. In adult muscles, COX VIII-H was the predominant isoform. The COX VIII-L mRNA was expressed 3 days after induction ofregeneration, and it progressively decreased after 7, 10, 14, and 30 days of regeneration in both muscles. In contrast, the expression ofCOX VIII-H mRNA accumulated as myogenesis proceeded to the myotubestage between 7 and 10 days of regeneration and progressively increasedto near control levels by 30 days. The influence of innervation on theexpression of COX VIII and -actin isoforms wasexamined in control, innervated, and denervatedregenerating muscles at 3 and 10 days. The relative expression of COXVIII-L mRNA in denervated regenerating EDL muscles was significantly greater, while that of COX VIII-H was significantlyless than in innervated regenerating EDL muscles after 10 days ofregeneration. Similarly, cardiac -actin mRNA levelswere elevated in denervated regenerating EDL muscles after 10 days ofregeneration. In conclusion, motor innervation influences thetransition from the COX VIII-L to COX VIII-H isoform during myogenesisin regenerating muscles.