H9c2(2-1) is a subclone of the original clonal cell line derived from embryonic BD1X rat heart tissue by B. Kimes and B. Brandt and exhibits many of the properties of skeletal muscle. This cell line was described to express myokinase, creatine phosphokinase and myosin. Myoblastic cells in this line will fuse to form multinucleated myotubes and respond to acetylcholine stimulation. Fusion occurs faster if the serum concentration in the medium is reduced to one percent.