Biochemical Studies on Dog Gastrocnemius Muscle after Leg-Lengthening. -On the Relaxing Factor System and the Actomyosin System-

Twenty-five adult mongrel clogs with an approximate body weight of 13 kg were subjected to Kawamura's lower leg lengthening operation and at 2 months after the operation an investigation on the muscle weight, the relaxing factor system and the actomyosin system of the gastrocnemius muscle was made. An electron-microscopic study was also made and the following results were obtained : 1. The weight of the control muscle following a 2-month immobilization of the knee joint by attaching a distraction apparatus, as compared against the opposed side normal muscle showed an approximate 50% decrease in wet weight and dry weight. The decreasing rate of muscle weight in the 10% leg lengthening group was likewise approximately 50% indicating no change as compared with that of the control muscle. In the 20% leg lengthening group, both wet weight and dry weight showed an approximate 60% decreasing rate. 2. The microsomal fraction of the normal muscle and the control muscle inhibited myofibrillar ATPase activity of the rabbit mixed muscle. Namely, the relaxing activity was approximately 90% and approximately 82% at Q=10 respectively. The relaxing activity of the microsomal fraction of the stretched muscle in the 10% leg lengthening group was approximately 80% at Q=10 and no great difference was seen as compared with the control group. In the 20% leg lengthening group, the relaxing activity was a mere 10% even at Q=20. 3. Caffeine (5～15 mM) in the presence of 2 mM K2-oxalate showed a mere 5% interference of the relaxing activity of the stretched muscle microsomal fraction. 4. The ATPase activity of the normal muscle and the control muscle microsomal fractions was 0.15 μmoles Pi/mg of protein/min and approximately 0.14 μmoles Pi/mg of protein/min respectively, and both showed typical ATP extra-splitting by an addition of 100 μM calcium. The ATPase activity of the stretched muscle microsomal fraction in the 10% leg lengthening group was approximately 0.17 μmoles Pi/mg of protein/min and while an addition of 100 μM calcium showed ATP extra-splitting likewise. The ATPase activity of the 20% leg lengthening group was approximately 0.10 μmoles Pi/mg of protein/min, and in this group absolutely no extra-splitting of ATP was produced by an addition of 100 μM calcium. 5. The myofibrillar ATPase activity of the normal muscle and the control muscle was approximately 0.60 μmoles Pi/mg of protein/20 minutes and approximately 0.56 //moles Pi/mg of protein/20 min, respectively. The myofibrillar ATPase activity of the stretched muscle in both the 10% and 20% leg lengthening groups showed no great difference as compared with that of the control muscle. 6. EGTA (5-100 μM), depending on its concentration inhibited the myofibrillar ATPase activity of the stretched muscle. The extent of the inhibition was approximately 50% in both the 10% and 20% leg lengthening groups when 20 μM EGTA was added and no great difference compared with that of the control group was seen. 7. The electron-microscopic picture, while in the 10% leg lengthening muscle hardly showing any morphological difference as compared against normal muscle, showed a decrease of glycogen granules in toto in the 20% leg lengthening group. 8. Concerning the above listed characters of the stretched muscle, no great difference was seen between the rapid lengthening group and gradual lengthening group. Thus it may be said that no influence of the lengthening speed was noted.