STUDIES OF EXCITABLE MEMBRANES .2. COMPARISON OF SPECIALIZATIONS AT NEUROMUSCULAR-JUNCTIONS AND NONJUNCTIONAL SARCOLEMMAS OF MAMMALIAN FAST AND SLOW TWITCH MUSCLE-FIBERS
STUDIES OF EXCITABLE MEMBRANES .2. COMPARISON OF SPECIALIZATIONS AT NEUROMUSCULAR-JUNCTIONS AND NONJUNCTIONAL SARCOLEMMAS OF MAMMALIAN FAST AND SLOW TWITCH MUSCLE-FIBERS
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DOI：
10.1083/jcb.68.3.752
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发表时间：
1976-01-01
影响因子：
7.8
通讯作者：
PORTER, KR
中科院分区：
文献类型：
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作者：
ELLISMAN, MH;RASH, JE;PORTER, KR
采用常规电镜和高压电镜对哺乳动物快、慢抽搐骨骼肌进行了冷冻骨折、厚、薄切片和组织化学技术的比较。尽管在相对较低的放大率下，在薄片上可以看到终板结构的大体形态学差异，但大鼠指长伸肌（EDL）（快速收缩）和比目鱼肌（慢收缩）纤维不能根据冷冻断裂暴露的突触前和突触后连接膜的分子特化的大小、数量或分布来区分。高压电子立体显微镜显示，连接褶皱近神经元部分皮层的特化是一个分支，阶梯状丝状网络，与假定的乙酰胆碱受体复合物相关。这些纤维可能参与限制受体蛋白向突触后膜的神经元周围移动。虽然EDL和比目鱼的连接膜看起来相似，但二级突触间隙的差异特化被注意到。比目鱼沟底部的细胞外基质呈有序的丝状梳状结构。这些丝状排列未在EDL连接处检测到。对EDL和比目鱼关节外肌柱的检查显示了额外的差异，这可能与电性和收缩性的变化有关。先前在大鼠膈肌某些纤维的肌柱中观察到的称为方形阵列的颗粒聚集体在EDL纤维的肌柱中大量存在，但在比目鱼纤维中很少见到。根据纤维类型之间的功能差异，讨论了膜的这些大体组成差异。
Mammalian fast and slow twitch skeletal muscles were compared by freeze-fracture, thick and thin sectioning and histochemical techniques using conventional and high voltage electron microscopy. Despite gross morphological differences in endplate structure visualized at relatively low magnifications in thin sections, rat extensor digitorum longus (EDL) (fast twitch) and soleus (slow twitch) fibers could not be distinguished on the basis of size, number or distribution of molecular specializations of the pre- and postsynaptic junctional membranes exposed by freeze fracturing. Specializations in the cortex of the juxtaneuronal portions of the junctional folds were revealed by high voltage electron stereomicroscopy as a branching, ladder-like filamentous network associated with the putative acetylcholine receptor complexes. These filaments may be involved in restricting the mobility of receptor proteins to the perineuronal aspects of the postsynaptic membrane. Although the junctional membranes of both EDL and soleus appeared similar, a differential specialization of the secondary synaptic cleft was noted. The extracellular matrix in the bottom of soleus clefts was observed as an ordered system of filamentous combs. These filamentous arrays were not detected in EDL junctions. Examination of the extrajunctional sarcolemmas of EDL and soleus revealed additional differences which may be correlated with variations in electrical and contractile properties. Particle aggregates termed square arrays previously described in the sarcolemmas of some fibers of the rat diaphragm were observed in large numbers in sarcolemmas of EDL fibers but were seldom encountered in soleus fibers. These gross compositional differences in the membranes are discussed in the light of functional differences between fiber types.