CYTOCHROME-C MESSENGER-RNA IN SKELETAL-MUSCLES OF IMMOBILIZED LIMBS

Even though immobilization of a slow skeletal muscle in a lengthened p osition prevents muscle atrophy, it is unknown whether this treatment would prevent a decrease in mitochondrial quantity. We found that, reg ardless of muscle length in immobilized limbs, the mRNA of a marker fo r mitochondrial quantity, cytochrome c, decreased. Cytochrome c mRNA p er milligram of muscle was 62 and 72% less 1 wk after fixation of the soleus muscle in shortened and lengthened positions, respectively, tha n age-matched controls. Cytochrome c mRNA per milligram wet weight was 36 and 32% less in the tibialis anterior muscle fixed for 1 wk in the shortened and length ened positions, respectively, compared with age- matched controls. Recently, in the 3'-untranslated region of cytochrom e c mRNA a novel RNA-protein interaction that decreases in chronically stimulated rat skeletal muscle was identified.[Z. Yan, S. Salmons, Y. L. Dang, M. T. Hamilton, and F. W. Booth. Am. J. Physiol. 271 (Cell P hysiol. 40): C1157-C1166, 1996]. The RNA-protein interaction in the 3' -untranslated region of cytochrome c mRNA in soleus and tibialis anter ior muscles was unaffected by fixation in either shortened or lengthen ed position. We conclude that, whereas lengthening muscle during limb fixation abates the loss of total muscle protein, the percentage decre ase in cytochrome c mRNA is proportionally greater than total protein. This suggests that the design of countermeasures to muscle atrophy sh ould include different exercises to maintain total protein and mitocho ndria.