The influence of innervation on differentiating tonic and twitch muscle fibres of the XXXX .

@entity1573 @entity8019
1. The anterior ( @entity8019 ) and posterior (PLD) latissimus dorsi muscles of adult @entity1573 were denervated by section of their motor nerves. Four weeks later the contractile and membrane properties of these muscles were studied in vitro at room temperature.2. Although the time course of the PLD muscle twitch was slightly prolonged, the qualitative difference in contractile characteristics of the slow @entity8019 and the fast PLD muscles was maintained after denervation.3. The difference in the passive membrane characteristics of the @entity8019 and PLD muscle fibres was not lost after denervation, although the membrane resistance (R(m)) and space constant (lambda) of the denervated muscles fell. The membrane resistance, space (lambda) and time (tau(m)) constants of the @entity8019 muscle remained significantly greater than for the PLD muscle fibres. The absolute values of tau(m) in both muscles increased, implying that in the case of the @entity8019 the membrane capacitance (C(m)) was increased above normal after denervation. This is discussed in terms of the ultrastructural changes in this muscle after denervation.4. The @entity8019 muscle was cut into small pieces and replaced in the bed of the PLD muscle, which in turn was minced and placed into the bed of the @entity8019 muscle. These muscles regenerated and became reinnervated by the PLD and @entity8019 nerves respectively. They aligned themselves in the muscle bed and adopted the former shape of the muscle that they replaced. The passive cable properties of the regenerated @entity8019 muscle fibres innervated by the PLD nerve resembled the control PLD fibres and the regenerated PLD fibres reinnervated by the @entity8019 nerve resembled those of the control @entity8019 . Regenerated @entity8019 and PLD reinnervated by their own nerves had contractile and membrane properties similar to those of control muscles.5. The results show that the fundamental differences, between slow and fast muscles once established, persist even when they are deprived of their innervation. The properties of developing muscle fibres however are determined by the motor nerves even in the adult animal.
