抄録
The contractile properties of chick fast PLD and slow ALD muscles in the early stage of development were examined. By the 17th day of incubation the contractile characteristics of these muscles became very different from each other. The PLD muscle consisted of at least two types of muscle fibers in the early stage of development, but the contraction of the ALD muscle was mono-phasic at the same stage. The contractile speed of the slow component in the PLD muscle did not coincide with that of the slow ALD muscle, the former being slower than the latter. The contraction of the biventer cervicis muscle consisting of fast and slow muscle fibers was also bi-phasic at birth, and the denervation at birth delayed the differentiation of the muscle. Dantrolene inhibited the twitch tension of both ALD and PLD muscles. The slow component of the PLD muscle was not reduced by administration of dantrolene. The inhibition caused by dantrolene in the PLD muscle became more remarkable with the lapse of days, suggesting the development of the T-system in the PLD muscle. The PLD and biventer cervicis muscles may provide a good preparation available for the examination of the process of differentiation of the chick muscle.
