Takekura H, Kasuga N, Kitada K, Yoshioka T
Department of Physiological Sciences, National Institute of Fitness and Sports, Kagoshima, Japan.
J Muscle Res Cell Motil. 1996 Aug;17(4):391-400. doi: 10.1007/BF00123356.
We observed the morphological features of the membrane systems (sarcoplasmic reticulum, transverse tubules and triads) involved with the excitation-contraction coupling in rat soleus and extensor digitorum longus muscle following two disuse protocols: denervation and immobilization. The immobilized positions were: maximum dorsal flexor (soleus were stretched and extensor digitorum longus were shortened), maximum plantar flexor (soleus were shortened and extensor digitorum longus were stretched), and midway between the dorsal flexor and plantar flexor. The arrangement of the membrane systems was disordered following both disuse conditions. Increases in transverse tubule network were apparent; there were clearly more triads than in normal fibres, and pentadic and heptadic structures (i.e., a close approximation of two or three transverse tubule elements with three or four elements of terminal cisternae of sarcoplasmic reticulum) were frequently appeared following both denervation and immobilization. The most notable difference between the influence of denervation and immobilization on the membrane systems is the time at which the pentads and heptads appeared. They appeared much earlier (1 week after denervation) in denervated than in immobilized (3 or 4 weeks after immobilization) muscle fibres. On the other hand, the frequency of pentads and heptads is clearly related to the fibre type (significantly higher in extensor digitorum longus) and to extent of atrophy. The different influences of immobilization in each leg position suggest that disuse, but with neurotrophic factor(s), influences on the membrane systems were affected by sarcomere length, and the neurotrophic factor(s) and muscle activity were not always necessary to form new membrane systems in disuse skeletal muscle fibres.
我们观察了大鼠比目鱼肌和趾长伸肌在两种废用方案（去神经支配和固定）后，参与兴奋 -收缩偶联的膜系统（肌浆网、横小管和三联体）的形态特征。固定位置为：最大背屈位（比目鱼肌被拉伸，趾长伸肌被缩短）、最大跖屈位（比目鱼肌被缩短，趾长伸肌被拉伸）以及背屈和跖屈之间的中间位置。在两种废用情况下，膜系统的排列均紊乱。横小管网络明显增加；三联体明显多于正常纤维，去神经支配和固定后均频繁出现五联体和七联体结构（即两个或三个横小管元件与肌浆网终池的三或四个元件紧密靠近）。去神经支配和固定对膜系统影响的最显著差异在于五联体和七联体出现的时间。它们在去神经支配的肌肉纤维中出现得更早（去神经支配后1周），而在固定的肌肉纤维中出现得较晚（固定后3或4周）。另一方面，五联体和七联体的频率明显与纤维类型有关（在趾长伸肌中显著更高），也与萎缩程度有关。每个腿部位置固定的不同影响表明，废用（但有营养因子）对膜系统的影响受肌节长度影响，并且在废用骨骼肌纤维中形成新的膜系统并不总是需要营养因子和肌肉活动。
