Krueger J W, London B
Adv Exp Med Biol. 1984;170:119-34. doi: 10.1007/978-1-4684-4703-3_11.
High resolution interference and phase microscopy were used to inspect the striations' appearance in shortening rat heart cells. Isolated cells were treated with detergent so that shortening could be graded by addition of calcium. Upon activation sarcomeres shortened to form (a) contraction densities in the middle of the A band at 1.7 micrometer (b) disappearance of the I bands and (c) phase brightening of the A bands at 1.6 micrometer and (d) dense Cz contraction bands at shorter lengths. These changes are totally consistent with the uniform sliding of myofilaments of previously accepted fixed dimensions. However, the striated patterns differed significantly in intact cells which were electrically stimulated to shorten. Here individual A bands remained distinct, without phase brightening or contraction band formation despite sarcomere shortening to less than the length of the A band as measured in the unstimulated cell. Maximal activation of intact cells by barium contracture elicited the full sequence of striation changes (a-d) seen in the chemically skinned cells. Light diffraction analysis gave comparable interpretation, i.e., the protein within the shortened sarcomere in the physiologically activated cardiac cell is more narrowly distributed than expected for thick filaments of fixed dimensions. These optical differences may reflect the restricted presence of the globular myosin heads at the ends of the cardiac sarcomere. This situation would explain the narrow range of the cardiac length-tension relation.
使用高分辨率干涉显微镜和相显微镜检查大鼠心脏细胞缩短时条纹的外观。将分离的细胞用去污剂处理，以便通过添加钙来对缩短程度进行分级。激活后，肌节缩短形成：(a) 在A带中部1.7微米处出现收缩密度；(b) I带消失；(c) 在1.6微米处A带相增亮；(d) 在更短长度时出现致密的Cz收缩带。这些变化与先前公认的固定尺寸的肌丝均匀滑动完全一致。然而，在电刺激缩短的完整细胞中，条纹模式有显著差异。尽管肌节缩短至小于未刺激细胞中测量的A带长度，但在这里单个A带仍然清晰可辨，没有相增亮或收缩带形成。通过钡挛缩对完整细胞进行最大激活，引发了在化学去表皮细胞中看到的完整条纹变化序列（a - d）。光衍射分析给出了类似的解释，即生理激活的心脏细胞中缩短肌节内的蛋白质分布比固定尺寸粗肌丝预期的更窄。这些光学差异可能反映了球状肌球蛋白头部在心脏肌节末端的有限存在。这种情况可以解释心脏长度 - 张力关系的狭窄范围。
