Effect of plaster-cast immobilization on the contractile properties of rabbit skeletal muscles of various functions.

The effect of plaster-cast immobilization was studied on the ATP-Ca++-induced contraction of glycerinated muscle fibres on myofibrillar superprecipitation and on the ATPase activity of gastrocnemius and soleus muscles obtained from rabbit hind limb. Following 28 days of immobilization the ATP-Ca++-induced tension of glycerinated muscle fibres prepared from the gastrocnemius and soleus muscles decreased significantly. Decreases in superprecipitation and in myofibrillar ATPase activity were less significant. It seems reasonable to conclude that the changes in the physiological parameters of isolated muscle fibres have been due to the alterations in the myofibrillar proteins induced by reduced activity of the muscles.