[Effect of the type of muscle fiber innervation on the acquisition of myofibrillar ATPase properties].

We present some observations differing from the idea that neurons precisely control the differentiation of muscle fibre histochemical properties and show that, in a few cases, innervation does not influence the development of myofibrillar ATPase properties. Moreover, we report that a regional variation of the acid stability of myofibrillar ATPase may occur in the polar zone of intrafusal fibres in chick PLD muscle spindles, a zone devoid of innervation. This observation is related to a similar variation in the polar zone of rat intrafusal fibres (Kucera et al., 1978). New examples are presented supporting the conclusion that the differentiation of the properties of ATPase activity, and thus of fibre types, takes place, at least in some cases, independently of the type of innervation received.