Searching for effective countermeasures to disuse muscle atrophy

采用尾部悬吊大鼠模型，探讨了肌肉萎缩的机制。我们还评估了在尾部悬吊期间穿插的周期性体重承重作为肌肉萎缩对策的有效性。将6周龄大鼠分为4组：悬吊组、悬吊间隔12小时/天（S组，12小时WB）、悬吊间隔1小时/天（S组，1小时WB）、对照组。停职2周。悬吊结束后，取趾长伸肌和比目鱼肌进行生理生化分析。比目鱼肌的整体效果比趾长伸肌更深刻。根据绝对张力（g）或单位湿重张力（g/mg）判断，悬浮引起比目鱼肌强直张力降低。这种减少并不完全归因于肌原纤维蛋白含量或浓度的降低。有人建议，其他因素比肌原纤维蛋白也参与了在强直张力的减少比目鱼肌。悬吊使比目鱼肌收缩更快。这是伴随着肌球蛋白重链（HC）同工酶组成的变化。除了HC 2a的表达百分比增加和HC 1的表达百分比降低外，还观察到肌球蛋白HC 2d和2b的新表达。每天负重1小时可部分抑制悬吊引起的变化。结果表明，将负重时间延长至每天12小时是更有效的对策。

Using tail-suspension model, we investigated the mechanism of muscle atrophy in the rat. We also evaluated the effectiveness of periodic body weight bearing interspersed during tail-suspension as a countermeasure to muscle atrophy. Six-week-old rats were divided into 4 groups ; Suspension, Suspension interspersed with 12hour of weight bearing per day(S with 12 hr WB), Suspension interspersed with 1 hour of weight bearing per day(S with 1 hr WB), Control. Suspension lasted for 2 weeks. At the end of suspension period, the extensor digitorum longus(EDL)and soleus muscles from the 4 groups were removed and subjected to physiological and biochemical analyzes.The results obtained in this study were as follows. Overall effects were much more profound on the soleus than on the EDL muscle. The suspension caused reduction in tetanic tension of the soleus muscle as judged either from absolute tension(g) or from tension per wet weight(g/mg). This reduction was not entirely attributable to a decrease in myofibrillar protein content or concentration. It was suggested that other factors than myofibrillar protein were also involved in the reduction in tetanic tension in the soleus muscle. The suspension made contraction of the soleus muscle faster. This was accompanied by the change in myosin heavy chain(HC) isozyme composition. A novel expression of myosin HC 2d and 2b were observed in addition to increased percentage expression of HC 2a and decreased percentage expression of HC 1. The body weight bearing for 1 hour per day partially suppressed suspension-induced changes. Prolongation of the time of the body weight bearing to 12 hours per day was shown to be a more effective as the countermeasure.