Borgers M, Thone F, Verheyen A, Ter Keurs H E
Histochem J. 1984 Mar;16(3):295-309. doi: 10.1007/BF01003613.
The requirement of calcium (Ca2+) in the excitation-contraction coupling of both skeletal and cardiac muscle is well established. However, the exact location of the intracellular storage sites of Ca2+ is not firmly established. We report here on the ultrastructural ultrastructural distribution of Ca2+ in white and red skeletal muscle and in cardiac muscle of the rat using combined phosphate-pyroantimonate (PPA) and oxalate-pyroantimonate (OPA) procedures. The methods are based on (a) stabilization and/or trapping of Ca2+ during the primary fixation step in glutaraldehyde by potassium phosphate or oxalate; (b) subsequent wash-out of all non-trapped cations such as Na+ and Mg2+ in potassium phosphate or oxalate; (c) conversion of the complexed or trapped Ca2+ into an electron-dense calcium pyroantimonate salt in 100 micron-thick tissue sections; and (d) wash-out of the excess potassium pyroantimonate at alkaline pH. With the OPA procedure, mitochondria of all muscle types showed little precipitate. The junctional sarcoplasmic reticulum was strongly reactive in relaxed white skeletal muscle, negative in contracted white fibres and negative in red skeletal and cardiac muscle, independent of the state of relaxation-contraction. Other organelles were essentially free of deposits. With the PPA method, the precipitate was almost exclusively confined to the sarcolemma and its T-tubular invaginations in cardiac and slow skeletal muscle, and was absent in fast skeletal muscle. Apart from occasional deposits in mitochondria, all other organelles were free of muscle. Apart from occasional deposits in mitochondria, all other organelles were free of precipitate. The sarcolemma-associated deposits were clearly confined to the inner leaflet of the lipid bilayer. The amount of precipitate varied within the contraction cycle, relaxed cells possessing the highest density. Exposure of the tissue to La3+ resulted in the complete absence of sarcolemma-bound precipitate suggesting that the Ca2+ is exchangeable. Furthermore, these cytological data suggest a basic difference in Ca2+ storage between white skeletal muscle on the one hand, and red skeletal and cardiac muscle on the other.
钙（Ca2+）在骨骼肌和心肌兴奋-收缩偶联中的需求已得到充分证实。然而，Ca2+在细胞内储存位点的确切位置尚未完全确定。我们在此报告使用磷酸焦锑酸盐（PPA）和草酸焦锑酸盐（OPA）联合方法，对大鼠白色和红色骨骼肌以及心肌中Ca2+的超微结构分布进行的研究。这些方法基于：（a）在戊二醛的初次固定步骤中，通过磷酸钾或草酸盐稳定和/或捕获Ca2+；（b）随后在磷酸钾或草酸盐中洗去所有未捕获的阳离子，如Na+和Mg2+；（c）在100微米厚的组织切片中将络合或捕获的Ca2+转化为电子致密的焦锑酸钙盐；（d）在碱性pH下洗去过量的焦锑酸钾。采用OPA方法时，所有肌肉类型的线粒体几乎没有沉淀。连接肌浆网在松弛的白色骨骼肌中反应强烈，在收缩的白色纤维中呈阴性，在红色骨骼肌和心肌中也呈阴性，与松弛-收缩状态无关。其他细胞器基本没有沉积物。采用PPA方法时，沉淀物几乎完全局限于心肌和慢收缩骨骼肌的肌膜及其T小管内陷处，而在快收缩骨骼肌中不存在。除了线粒体偶尔有沉积物外，所有其他细胞器都没有沉淀物。与肌膜相关的沉积物明显局限于脂质双层的内小叶。沉淀物的量在收缩周期内有所变化，松弛细胞中的密度最高。将组织暴露于La3+会导致肌膜结合沉淀物完全消失，这表明Ca2+是可交换的。此外，这些细胞学数据表明，一方面白色骨骼肌与另一方面红色骨骼肌和心肌在Ca2+储存方面存在基本差异。
