Role of nerve and tension in maturation of posthatching slow-tonic muscle in chicken

The role of motor innervation and muscle tension in the posthatching maturation of the slow-tonic anterior latissimus dorsi (ALD) muscle of the chicken has been investigated. Modification of the muscle tension was obtained either by maintaining ALD in a shortened state or by stretching, after or without denervation. In denervated as well as in innervated ALD, shortening resulted in atrophy and inhibition of developmental change in muscle fiber population. In contrast, stretch causes hypertrophy, transformation of all 3B fibers, increase in SM2 isomyosin expression, and decrease in Ca2+-activated myosin ATPase in innervated or denervated ALD. On the other hand oxidative activity in ALD fibers was strikingly reduced after denervation even in presence of stretch-induced hypertrophy. This study suggests that a passive stretch can be involved in some, but not all, changes in ALD characteristics occurring after denervation and may be also involved in normal posthatching development of the slow-tonic muscle. Possible clinical implications of these results in relation to treatments for preventing muscle atrophy resulting from immobilization or disuse are suggested.