QUANTITATIVE-ANALYSIS OF DYSTROPHIN IN FAST-TWITCH AND SLOW-TWITCH MAMMALIAN SKELETAL-MUSCLE

The relative tissue content of dystrophin has been evaluated in the slow-twitch soleus (primarily type I fibers) and fast-twitch vastus lateralis (primarily type IIb filbers) muscles of the rat and mouse, as well as in human biopsy samples from the vastus lateralis and gluteus maximus muscles, using a sensitive immunochemical assay. The dystrophin content of the soleus muscle was approximately twofold higher than in the vastus lateralis muscle. This difference is not entirely explained by the higher total sarcolemmal surface of the smaller soleus muscle type I fibers, and is therefore attributed to a higher content of dystrophin in the type I fibers compared to type IIb fibers. PCR analysis of the dystrophin transcript levels in the two muscle types indicated no significant differences. Analysis of human muscle biopsies revealed a twofold higher dystrophin content in the vastus lateralis muscle compared to the gluteus maximum muscle. It is concluded that the tissue content of dystrophin may vary significantly among physiologically different skeletal muscle types.