An In Vitro Contraction Model in Mouse Primary Cultured Myotubes Using Satellite Cells Originated from the EDL and Soleus Muscles

Purpose: Skeletal muscle cell lines such as mouse C2C12 cells and rat L6 cells often show abnormal characteristics because of repeated-passage cultures and artificial culture conditions. Primary myotubes are considered to retain their in vivo properties. Here, satellite cells originating from the extensor digitorum longus (EDL) or soleus muscle were differentiated into primary myotubes and used for an in vitro contraction model. Materials and Methods: Satellite cells from the mouse EDL or soleus were isolated by a single-fiber isolation method. We examined the formation of the sarcomere assemblies by α-actininimmunostaining in the differentiated myotubes. We also investigated the contractile characteristics of myotubes stimulated with an electric pulse and insulin induced-glucose uptake. C2C12 myotubes were used for comparison with the primary myotubes. Results and Discussion: The sarcomere assemblies were observed in the primary myotubes but hardly observed in the C2C12 myotubes. The number of myotubes responding to stimulation by the electric pulse was increased in both the C2C12 and primary myotubes, although the movement in the primary myotubes was larger than that in C2C12 myotubes. The glucose uptake stimulated by insulin was significantly increased compared to the basal uptake in the primary myotubes and the C2C12 myotubes. These data suggest that the mouse primary myotubes, with their greater number of sarcomere assemblies and higher level of contractive activity, will be valuable as an in vitro contraction model that can be used in place of cell lines or human primary myotubes.