CYTOCHROME-C PROMOTER ACTIVITY IN SOLEUS AND WHITE VASTUS LATERALIS MUSCLES IN RATS

Cytochrome c protein and mRNA are 300 and 100% higher, respectively, i n the soleus muscle (predominantly slow-twitch oxidative) than the whi te vastus lateralis (predominately fast-twitch glycolytic) muscle (W.W .Winder, K. M. Baldwin, and J. O. Holloszy. Eur. J. Biochem. 47: 461-4 67, 1974; M. M. Lai and F. mi Booth. J. Appl. Physiol. 69: 843-848, 19 90). However, the mechanisms controlling these differences in cytochro me c mRNA are largely unknown. The present study employed direct plasm id injection techniques to determine whether the proximal promoter (-7 26 to +610) of the rat somatic cytochrome c gene was more active in th e soleus than in white vastus lateralis muscles in rats. No difference between the soleus and white vastus lateralis muscles for the activit ies of the -726, -631, -489, -326, -215, -159 and -149 cytochrome c pr omoters was noted. The results of this study suggest that additional e lements (outside of -726 to +610) in the cytochrome c gene may be requ ired, or posttranscriptional regulation may account, for the higher cy tochrome c mRNA in the slow-twitch oxidative muscle.