Development of acetylcholine sensitivity during myogenesis

Abstract

The development of acetylcholine (ACh) sensitivity during myogenesis has been studied by iontophoretic application of ACh and intracellular recording from myogenic cells from rat forelimbs cultured in vitro. The fine structure of the cells was then examined by electron microscopy. The development of ACh sensitivity is correlated with the appearance of thick and thin filaments and precedes myofibril formation. All myotubes are sensitive to ACh. Myogenic cells arising by cell division in vitro can become sensitive to ACh and construct myofibrils without cell fusion. When cell fusion is inhibited by calcium ion deficiency or when cell division is blocked by FUdR, many mononucleate, striated, ACh-sensitive cells appear in culture. While ACh sensitivity appears at the onset of muscle differentiation, ACh receptors seem to play no role in the early events of myogenesis, as evidenced by the failure of receptor block or of desensitization to interfere with myogenesis. The concurrent appearance of myofilaments and ACh sensitivity is discussed in relation to the early events and control mechanisms of myogenesis.