Developmental changes in fiber type-related proteins in soleus, rectus femoris, and heart muscles of normal and dystrophic mice.

By using sensitive enzyme immunoassay methods, several isoenzymes or isoproteins related to muscle fiber types were determined in the soleus (SOL), rectus femoris (RFM), and heart muscles of normal and dystrophic (dy/dy) mice of various ages. In normal adult mice, the S-100 protein alpha subunit (S-100 alpha) and creatine kinase B subunit (CK-B), which are known to be distributed predominantly in type I muscle fibers as S-100a0 (alpha alpha form of the S-100 protein) and the MB form of CK, respectively, were enhanced several-fold in the "aerobic" SOL muscle as compared with the "anaerobic" RFM muscle. The enolase beta subunit (beta-enolase) and the M subunit of CK (CK-M) were present in the RFM at levels increased several-fold compared to levels in the SOL of the same mice. In age-matched dystrophic adult mice, however, the compositions of these muscle-related proteins in the RFM muscle shifted to those of the SOL muscle: S-100 alpha and CK-B increased several-fold, beta-enolase and CK-M decreased markedly as compared with the normal RFM. On the other hand, the SOL and heart muscles of dystrophic mice showed only a slight increase of CK-B or decrease of CK-M. In the RFM of 3-week-old dystrophic mice, S-100 alpha and beta-enolase levels were similar to those in the RFM of control littermates, but a significant increase of CK-B and a decrease of CK-M were already observed in this early stage of dystrophy. These results indicate that changes in muscle-related proteins in the dystrophic muscles are apparently displayed mainly in the anaerobic muscles and feature a decrease in type II fiber-related proteins and a relative increase in type I fiber-related proteins. The mechanism of these changes in dystrophic mice is discussed.