Cytochrome c promoter activity in soleus and white vastus lateralis muscles in rats

Abstract

Cytochrome c protein and mRNA are 300 and 100% higher, respectively, in the soleus muscle (predominantly slow-twitch oxidative) than the white vastus lateralis (predominately fast-twitch glycolytic) muscle (W. W. Winder, K. M. Baldwin, and J. O. Holloszy. Eur. J. Biochem. 47: 461–467, 1974; M. M. Lai and F. W. Booth. J. Appl. Physiol. 69: 843–848, 1990). However, the mechanisms controlling these differences in cytochrome c mRNA are largely unknown. The present study employed direct plasmid injection techniques to determine whether the proximal promoter (−726 to +610) of the rat somatic cytochrome c gene was more active in the soleus than in white vastus lateralis muscles in rats. No difference between the soleus and white vastus lateralis muscles for the activities of the −726, −631, −489, −326, −215, −159 and −149 cytochrome c promoters was noted. The results of this study suggest that additional elements (outside of −726 to +610) in the cytochrome c gene may be required, or posttranscriptional regulation may account, for the higher cytochrome c mRNA in the slow-twitch oxidative muscle.