NA,K-ATPASE EXPRESSION IN C-2(C-12) CELLS DURING MYOGENESIS - MINIMAL CONTRIBUTION OF ALPHA-2 ISOFORM TO NA,K TRANSPORT

Cells of the murine skeletal muscle line, C2C12, undergo differentiation from mononuclear myoblasts to multinuclear myo-tubes that express a number of proteins associated with striated muscle. We examined the relationship between the abundance of the mRNAs encoding the fast-twitch Ca-ATPase and the alpha isoforms of Na,K-ATPase and the subsequent expression of their respective polypeptides. Both the mRNA and protein levels of the alpha1 isoform remained constant throughout differentiation. In contrast, the content of mRNAs encoding the alpha2 isoform and fast-twitch Ca-ATPase increased coordinately with the abundance of their corresponding polypeptides during myotube development. Despite the dramatic increase in alpha2 expression, estimates of in vitro Na,K-ATPase activity and assessments of in vivo transport activity suggest that alpha2 contributes little to ionic homeostasis in C2C12 myotubes.