Ohira Yoshinobu, Yoshinaga Tomoo, Ohara Makoto, Kawano Fuminori, Wang Xiao Dong, Higo Yoko, Terada Masahiro, Matsuoka Yoshikazu, Roy Roland R, Edgerton V Reggie
Graduate School of Medicine, Osaka University, Osaka, Japan.
Cells Tissues Organs. 2006;182(3-4):129-42. doi: 10.1159/000093963.
The relative importance of neural and mechanical influences in maintaining normal slow and fast muscle properties remains unclear. To address this issue, we studied the effects of 10 days of hindlimb unloading (HU) with or without tenotomy and/or denervation on the cross-sectional area (CSA), myosin heavy chain (MHC) expression (immunohistochemistry) and composition (gel electrophoresis), and myonuclear number in soleus and plantaris fibers in adult male Wistar rats. In general, the adaptations in fiber type and size were similar using either single fiber gel or immunohistochemical analyses. HU resulted in atrophy of type I and I+IIa/x MHC fibers in the soleus and in type I, I+IIa/x, IIa/x, IIa/x+IIb, and IIb MHC fibers in the plantaris. Addition of tenotomy and/or denervation in HU rats had minimal effects on fiber CSA in the soleus, but fiber CSA in the plantaris further decreased, particularly in fibers expressing only fast MHCs. HU resulted in a de novo appearance of type I+IIa/x+IIb and IIa/x+IIb MHC fibers in the soleus and of type I+IIa/x+IIb MHC fibers in the plantaris. Tenotomy and/or denervation in HU rats had no further effect on the fiber type composition of either muscle. Mean myonuclear number/mm of type I fibers was decreased in the soleus of HU rats, and increased in type I and I+IIa/x fibers in HU plus tenotomy (HU+Ten) rats. In the plantaris, mean myonuclear number/mm of type IIa/x, IIa/x+IIb, and IIb fibers was lower after HU with or without tenotomy and/or denervation. Mean cytoplasmic volume/myonucleus ratio of type I and I+IIa/x fibers in the soleus of the HU group tended to be smaller than in controls. The largest decrease was noted in the HU+Ten group. In the plantaris, this ratio was unaffected by HU alone, but was decreased by addition of tenotomy and/or denervation when all fiber types were combined. These data indicate that the major cause of fiber atrophy and adaptations in myonuclear domain size in the slow soleus of HU rats is the chronic reduction in force generation, whereas the elimination of neuromuscular contact via denervation results in additional fiber atrophy and adaptations in myonuclear domain size in the fast plantaris.
神经和机械因素在维持正常慢肌和快肌特性方面的相对重要性仍不清楚。为了解决这个问题，我们研究了成年雄性Wistar大鼠在进行10天的后肢卸载（HU）时，无论有无肌腱切断术和/或去神经支配，对比目鱼肌和跖肌纤维的横截面积（CSA）、肌球蛋白重链（MHC）表达（免疫组织化学）和组成（凝胶电泳）以及肌核数量的影响。一般来说，使用单纤维凝胶或免疫组织化学分析，纤维类型和大小的适应性变化相似。HU导致比目鱼肌中I型和I+IIa/x MHC纤维萎缩，以及跖肌中I型、I+IIa/x、IIa/x、IIa/x+IIb和IIb MHC纤维萎缩。在HU大鼠中添加肌腱切断术和/或去神经支配对比目鱼肌纤维CSA的影响最小，但跖肌纤维CSA进一步降低，特别是在仅表达快肌MHC的纤维中。HU导致比目鱼肌中出现I+IIa/x+IIb和IIa/x+IIb MHC纤维，跖肌中出现I+IIa/x+IIb MHC纤维。HU大鼠中的肌腱切断术和/或去神经支配对任何一块肌肉的纤维类型组成都没有进一步影响。HU大鼠比目鱼肌中I型纤维的平均肌核数量/mm减少，而在HU加肌腱切断术（HU+Ten）大鼠的I型和I+IIa/x纤维中增加。在跖肌中，无论有无肌腱切断术和/或去神经支配，HU后IIa/x、IIa/x+IIb和IIb纤维的平均肌核数量/mm都较低。HU组比目鱼肌中I型和I+IIa/x纤维的平均细胞质体积/肌核比率往往小于对照组。HU+Ten组的下降幅度最大。在跖肌中，该比率单独受HU影响不大，但当所有纤维类型合并时，添加肌腱切断术和/或去神经支配会使其降低。这些数据表明，HU大鼠慢比目鱼肌中纤维萎缩和肌核域大小适应性变化的主要原因是力量产生的慢性减少，而通过去神经支配消除神经肌肉接触会导致快跖肌中额外的纤维萎缩和肌核域大小的适应性变化。
