Wissocq J C
Arch Anat Microsc Morphol Exp. 1978;67(1):37-62.
The longitudinal fibres from atokous Nereis belong to the double oblique striation type. Their thick myofilaments, paramyosinic (about 145 A periodicity) are arranged in an hexagonal lattice, well preserved after a glycerol treatment. 9 to 13 thin filaments form an orbit around one thick filament (ratio: 6-7/1). The contraction occurs in two processes: a sliding filament mechanism, and a shearing mechanism. This second mechanism consists in a parallel shifting of thick filaments, arising their overlap and decreasing their degree of stagger; it induces the increase of the myofibrillar (A-bands) oblique angle from 10-12 degrees in isolated glycerol extracted fibres, to 35-38 degrees in the same fibres after contraction by the action of ATP-solution. The longitudinal fibres from epitokous Nereis or Heteronereis are characterized also by a double oblique striation. The structural aspects of the contraction are similar to these ones occurring in atokous fibres. Nevertheless, the epitokous fibres are different from the atokous fibres by many characteristic points. Their thick myofilaments, with an hexagonous array, are thinner and shorter than these ones from atokous fibres. The contractile material is only present in the cortex. The axis of epitokous fibres is filled with numerous mitochondria, between them numerous glycogen particles have been synthetised. The sarcoplasm of the fiber's coelomic edge is often devoided of myofilaments but it is full of mitochondria and glycogen granules. The nucleus, with a voluminous nucleolus, is no more placed in the fibre axis, but in a lateral sarcoplasm containing ribosomes, glycogen and mitochondria. The important transformations of longitudinal fibres are discussed in connection with the Heteronereis locomotor behaviour, very different from this one of the atokus Nereis. Particularly, it seems that the abundance of glycogen and mitochondria in epitokous muscles allows a high contraction frequency. The decrease of the diameter and length from the thick filaments should be set in relation with the augmentation of the contraction's swiftness. These results are very similar to these ones occuring in Syllidae with the stolonization mode of reproduction. The Syllis stolonial fibres present the same characteristics than the Nereis epitokous fibres.
无性态沙蚕的纵肌纤维属于双斜纹类型。它们的粗肌丝，副肌球蛋白（约145埃周期性）呈六边形晶格排列，经甘油处理后保存良好。9至13根细肌丝围绕一根粗肌丝形成一个轨道（比例：6 - 7/1）。收缩发生在两个过程中：滑动丝机制和剪切机制。第二种机制是粗肌丝的平行移动，导致它们的重叠增加并减少错开程度；这会使肌原纤维（A带）的斜角从分离的甘油提取纤维中的10 - 12度增加到在ATP溶液作用下收缩后同一纤维中的35 - 38度。有性态沙蚕或异沙蚕的纵肌纤维也具有双斜纹特征。收缩的结构方面与无性态纤维中发生的情况相似。然而，有性态纤维在许多特征点上与无性态纤维不同。它们呈六边形排列的粗肌丝比无性态纤维的更细更短。收缩物质仅存在于皮层中。有性态纤维的轴充满了大量线粒体，在它们之间合成了许多糖原颗粒。纤维体腔边缘的肌浆通常没有肌丝，但充满了线粒体和糖原颗粒。有一个大核仁的细胞核不再位于纤维轴上，而是位于含有核糖体、糖原和线粒体的侧肌浆中。结合异沙蚕与无性态沙蚕非常不同的运动行为，讨论了纵肌纤维的重要转变。特别是，有性态肌肉中丰富的糖原和线粒体似乎允许高收缩频率。粗肌丝直径和长度的减小应与收缩速度的增加相关联。这些结果与多毛纲动物以匍匐茎繁殖方式时出现的结果非常相似。多毛纲动物的匍匐茎纤维与沙蚕有性态纤维具有相同的特征。
