Bennett P M, Elliott A
MRC Cell Biophysics Unit, King's College London, UK.
J Muscle Res Cell Motil. 1989 Aug;10(4):297-311. doi: 10.1007/BF01758426.
A method for quick-freezing muscles while observing their mechanical properties until the moment of freezing is described. This method was used to freeze the anterior byssus retractor muscle (ABRM) of Mytilus edulis. Intact muscle in the presence of sucrose as a cryoprotectant was freeze-substituted in acetone, fixed and embedded for electron microscopy. ABRM was frozen in a number of mechanical states including 'catch', the state of high passive tension particularly associated with some molluscan muscles. Transverse sections were examined to determine the distribution of filaments in the muscle cells. In the relaxed muscle thick and thin filaments are fairly randomly distributed. Groups of thin filaments and of thick filaments are often seen, and there is no obvious association between the two types of filaments. In contrast, in rigor muscles, both glycerol-extracted and intact, most of the thin filaments were found to lie in rings or rosettes around the thick filaments. In some places bridges between thick and thin filaments could be distinguished. In actively contracting muscle (phasic contraction) the appearance is intermediate between that of the relaxed and rigor muscles. Many thick filaments are surrounded by rosettes of thin filaments but many of the thin filaments are grouped and have no connections with thick filaments. The 'catch' state, left after a period of tonic contraction, is similar in its distribution of thick and thin filaments to the active state, many of the thin filaments lying between the thick. Frequently thick and thin filaments seem to be closer together than in other states of the muscle where a pronounced exclusion zone is present around the thick filaments. There is no evidence for association between the thick filaments. The different distribution of thin filaments in the different states is consistent with the previously described X-ray diffraction data if it is assumed that most of the contribution to the equatorial reflection at 12 nm comes from the groups of thin filaments. Our data support a model for catch in which there is a change in the association between thick and thin filaments, rather than one in which thick filaments are clumped.
本文描述了一种在观察肌肉力学特性直至冻结瞬间的同时对其进行快速冷冻的方法。该方法用于冷冻紫贻贝的前足丝牵缩肌（ABRM）。在作为冷冻保护剂的蔗糖存在下，将完整的肌肉在丙酮中进行冷冻置换，固定并包埋用于电子显微镜观察。ABRM在多种力学状态下被冷冻，包括“捕捉”状态，即一种特别与某些软体动物肌肉相关的高被动张力状态。检查横向切片以确定肌细胞中细丝的分布。在松弛的肌肉中，粗丝和细丝相当随机地分布。经常可以看到细丝群和粗丝群，并且两种类型的细丝之间没有明显的关联。相比之下，在僵直肌肉中，无论是甘油提取的还是完整的，大部分细丝都位于粗丝周围的环或玫瑰花结中。在某些地方，可以区分粗丝和细丝之间的桥。在主动收缩的肌肉（相位收缩）中，外观介于松弛肌肉和僵直肌肉之间。许多粗丝被细丝的玫瑰花结包围，但许多细丝聚集在一起，与粗丝没有连接。在一段时间的强直性收缩后留下的“捕捉”状态，其粗丝和细丝的分布与活动状态相似，许多细丝位于粗丝之间。粗丝和细丝之间似乎比在肌肉的其他状态下更靠近，在其他状态下粗丝周围存在明显的排斥区。没有证据表明粗丝之间存在关联。如果假设对12nm赤道反射的大部分贡献来自细丝群，那么细丝在不同状态下的不同分布与先前描述的X射线衍射数据一致。我们的数据支持一种捕捉模型，其中粗丝和细丝之间的关联发生了变化，而不是粗丝聚集的模型。
