DIFFERENTIAL MYOGENICITY OF SATELLITE CELLS ISOLATED FROM EXTENSOR DIGITORUM LONGUS (EDL) AND SOLEUS RAT MUSCLES REVEALED IN-VITRO

Following muscle damage, fast-and slow-contracting fibers regenerate, owing to the activation of their satellite cells, In rats, crush-induc ed regeneration of extensor digitorum longus (EDL, a fast muscle) and soleus (a slow muscle) present different characteristics, suggesting t hat intrinsic differences exist among their satellite cells. An in vit ro comparative study of the proliferation and differentiation capaciti es of satellite cells isolated from these muscles is presented there, We observed several differences between soleus and EDL satellite cell cultures plated at high density on gelatin-coated dishes. Soleus satel lite cells proliferated more actively and fused into myotubes less eff iciently than EDL cells. The rate of muscular creatine kinase enzyme a ppeared slightly lower in soleus than in EDL cultures at day 11 after plating, when many myotubes were formed, although the levels of muscul ar creatine kinase mRNA were similar in both cultures. In addition, so leus cultures expressed higher levels of MyoD and myogenin mRNA and of MyoD protein than EDL satellite cell cultures at day 12. A clonal ana lysis was also carried out on both cell populations in order to determ ine if distinct lineage features could be detected among satellite cel ls derived from EDL and soleus muscles, When plated on gelatin at clon al density, cells from both muscles yielded clones within 2 weeks, whi ch stemmed from 3-15 mitotic cycles and were classified into three cla sses according to their sizes. Myotubes resulting from spontaneous fus ion of cells from the progeny of one single cell were seen regardless of the clone size in the standard culture medium we used, The proporti on of clones showing myotubes in each class depended on the muscle ori gin of the cells and was greater in EDL- than in soleus-cell cultures, In addition, soleus cells were shown to improve their differentiation capacity upon changes in the culture condition. Indeed, the proportio ns of clones showing myotubes, or of cells fusing into myotubes in clo nes? were increased by treatments with a myotube-conditioned medium, w ith phorbol ester, and by growth on extra-cellular matrix components ( Matrigel). These results, showing differences among satellite cells fr om fast and slow muscles, might be of importance to muscle repair afte r trauma and in pathological situations.