Dalen H, Scheie P
Laboratory of Clinical Electron Microscopy, University of Bergen, Norway.
Acta Physiol Scand Suppl. 1991;599:47-60.
Rat myocardial tissue, both fresh and chemically fixed, was quench frozen in melting Freon 22 at rates that resulted in in the formation of large ice-crystals. The material was studied with both scanning and transmission electron microscopy. Particular attention was paid to the characteristic freezing patterns within the myofibrils and mitochondria, and to features exposed by such freezing that might otherwise remain obscured. The freezing patterns found in tissue subjected to different processes were compared with the ultrastructure of unfrozen, chemically fixed counterparts. Ice-crystal cavities in the contractile material varied considerably along the length of a given myofiber in which the freezing front had progressed in parallel with the long axis of the myofibers. It is suggested that the intercalated disc functioned as a barrier to the freezing process. Ice generally compressed and distorted the contractile material beyond recognition, although the positions of the Z-bands remained evident and in register. Most single-fixed mitochondria were devoid of visible ice-crystal cavities, and the cristae generally remained intact. On the other hand, ice-crystal cavities were commonly seen between cristae of double-fixed mitochondria. No signs of perforations were seen in lipid bilayer membranes. Numerous strand-like connections between mitochondria as well as between mitochondria and the myofibrillar surface, which were believed to be sarcotubules, were made visible by the slow freezing process. Other strands, transverse to the myofibrils, connecting adjacent Z-bands and joining Z-bands to the sarcolemma, were interpreted as cytoskeletal elements. These strands, together with what apparently were SR tubules, exhibited high resistance to the stresses associated with the formation of ice-crystals.
对新鲜的和化学固定的大鼠心肌组织，在融化的氟利昂22中以能形成大冰晶的速率进行骤冷冷冻。用扫描电子显微镜和透射电子显微镜对该材料进行了研究。特别关注了肌原纤维和线粒体内的特征性冷冻模式，以及这种冷冻所暴露的、否则可能仍被掩盖的特征。将经过不同处理的组织中的冷冻模式与未冷冻的、化学固定的对应组织的超微结构进行了比较。收缩物质中的冰晶腔沿给定肌纤维的长度变化很大，在该肌纤维中，冷冻前沿与肌纤维的长轴平行推进。有人认为闰盘起到了冷冻过程的屏障作用。冰通常会压缩并扭曲收缩物质，使其难以辨认，尽管Z带的位置仍然清晰且对齐。大多数单次固定的线粒体没有可见的冰晶腔，嵴通常保持完整。另一方面，在两次固定的线粒体的嵴之间常见到冰晶腔。在脂质双分子层膜中未观察到穿孔迹象。通过缓慢冷冻过程，线粒体之间以及线粒体与肌原纤维表面之间的许多丝状连接（被认为是肌小管）变得可见。其他与肌原纤维横向的细丝，连接相邻的Z带并将Z带与肌膜相连，被解释为细胞骨架成分。这些细丝，连同明显是肌浆网小管的结构，对与冰晶形成相关的应力表现出高抗性。
