The formation of myotubes in cultures of chick embryo myogenic cells in serum-free medium is induced by the insulin pulse treatment.

A simple chemically defined medium is described which in primary cultures promotes differentiation of cells form embryonic chicken breast muscle to myotubes and cross-striated myofibres. It is shown that 5 minute pulse treatment of the myogenic cells with the insulin containing solution is sufficient to switch on, in all-or-nothing manner the processes of myotube formation. Supplementation of Eagle's minimal essential medium (EMEM) with Dextran T-500, microelements, Thiodiethanol, and catalase, and incubation of the cultures at 35 degrees C instead at 37 degrees C, provided conditions promoting myotube terminal differentiation to cross-striated myofibres. These myofibres showed well-developed sarcomeres and were capable of spontaneous contractions.