The Influence of Limb Immobilization and Exercise on the Structure and Function of Mouse Soleus Muscle

本研究旨在探讨每日运动对小鼠后肢悬吊所致比目鱼肌废用性萎缩的改善作用。将小鼠分为对照组（CON）、后肢悬吊组（HS）和后肢悬吊加运动组（HS- ex）进行生理、组织学和形态计量学检查。在检查该肌肉的收缩功能后，立即采用腺苷三磷酸酶染色将其分为1型或2型纤维。研究了两种纤维及其运动终板细胞质细胞器的超微结构，并从形态计量学和质量上进行了比较。HS组比目鱼肌活动降低到正常组的2/3以下，HS- ex组比目鱼肌活动增加到正常组的1.4倍以上。HS组大鼠最大抽搐张力和强直张力小于CON组，HS- ex组大鼠最大抽搐张力和强直张力明显大于HS组。HS减少了1型和2型纤维的大小，并增加了1型纤维的百分比，但HS- ex肌肉没有。HS- ex后少量肌原纤维萎缩，HS后许多肌原纤维1、2号纤维肌节变性。HS组终板显示出大量变性和再生的超微结构证据，而HS- ex组终板受影响较小。2型纤维终板的结构改变程度大于1型终板。这表明1型终板比2型终板更能抵抗退行性改变。与对照组相比，HS后1和2纤维线粒体体积分数均降低，而HS- ex仅2纤维线粒体体积分数降低。这些数据表明运动训练可以显著减弱HS对比目鱼肌的有害影响。

This study was undertaken to determine the amelioration effect of a daily exercise on disuse atrophy of mouse soleus induced by hindlimb suspension. Physiologic, histologic and morphometric examination were made on mice were divided into control (CON), hindlimb suspension (HS) and HS plus exercise (HS-EX) with daily treadmill running. Immediately after checking the contractile function of this muscle, Adenosine triphosphatase staining was employed to classify into type 1 or 2 fibers. The ultrstructure of the cytoplasmic organelles of both fibers and their motor endplates were studied and compared morphometrically or qualitively. The soleus muscle activity was reduced to below 2/3 on HS, but increased to over 1.4 times of its normal activity on HS-EX. Maximum twitch and tetanic tensions in the HS group were less than those in CON, with those HS-EX being significantly greater than those in HS. HS reduced the size of both type 1 and 2 fibers and and increased the percentage of type 1 fibers, but not in the HS-EX muscles. Atrophy of a few myofibrills was observed after HS-EX, wheras after HS many myofibrills showed degeneration of the sarcomere of both 1 and 2 fibers. Endplates in the HS group were found to exhibit a great deal of ultrastructual evidence of degeneration and regeneration, but those in the HS-EX group were less affected. The endplates in 2 fibers exhibited structural alteration to a greater extent than type 1 endplates in HS alone. This suggests that type 1 endplates were more resistant to degenerative changes than the 2 fibers. The mitochondrial volume fraction after HS decreased both in the 1 and 2 fibers, whereas it diminished only in the 2 fibers HS-EX as compared with the values in the CON. These data show that exercise training can markedly attenuate the detrimental effects of HS on the soleus muscle.