EFFECT OF DENERVATION AND DYSTROPHY ON ADAPTATION OF SARCOMERE NUMBER TO FUNCTIONAL LENGTH OF MUSCLE IN YOUNG AND ADULT MICE

  • 1 January 1976
    • journal article
    • research article
    • Vol. 122  (NOV) , 455-465
Abstract
In young animals the elongation of the limb bones increases the functional length of the muscles. In adult animals the functional length of a muscle can be increased by immobilizing it in the lengthened position. In both cases the muscle adapts by adding on more sarcomeres in series. The role of the nerve supply in this adaptation was investigated using denervated mouse muscles and muscles from dystrophic mice where there was thought to be an abnormality of the nerve supply. Post-natal sarcomere addition in denervated muscles falls short of that of controls. The nerve supply is necessary for normal addition of sarcomeres, however a change in gait resulting from denervation also affects the sarcomere number. Sarcomere number in fully grown mice is not affected by denervation nor is the ability of the muscle to adapt to immobilization in the lengthened position. This is true for the fast twitch biceps brachii and the slow twitch soleus muscle. In dystrophic muscles post-natal sarcomere addition is normal, although with a few short fibers some muscle fibers cannot adapt to increase in the functional length of the muscle due to bone growth. Adult dystrophic muscle is capable of adapting to immobilization in the lengthened position. However, although the total number of additional sarcomeres is the same as in normal immobilized muscle, additions are at a slower rate. Although denervated and dystrophic muscle fibers are in a state of atrophy, they are still capable of adding on sarcomeres in series when the functional length of the muscle is increased. The mechanism which enables the muscle to respond in this way to an increased functional length does not involve the nerve supply.