Oschman J L, Wall B J
J Cell Biol. 1972 Oct;55(1):58-73. doi: 10.1083/jcb.55.1.58.
Flame photometry reveals that glutaraldehyde and buffer solutions in routine use for electron microscopy contain varying amounts of calcium. The presence of electron-opaque deposits adjacent to membranes in a variety of tissues can be correlated with the presence of calcium in the fixative. In insect intestine (midgut), deposits occur adjacent to apical and lateral plasma membranes. The deposits are particularly evident in tissues fixed in glutaraldehyde without postosmication. They are also observed in osmicated tissue if calcium is added to wash and osmium solutions. Deposits are absent when calcium-free fixatives are used, but are present when traces of CaCl(2) (as low as 5 x 10(-5)M) are added. The deposits occur at regular intervals along junctional membranes, providing images strikingly similar to those obtained by other workers who have used pyroantimonate in an effort to localize sodium. Other divalent cations (Mg(++), Sr(++), Ba(++), Mn(++), Fe(++)) appear to substitute for calcium, while sodium, potassium, lanthanum, and mercury do not. After postfixing with osmium with calcium added, the deposits can be resolved as patches along the inner leaflet of apical and lateral plasma membranes. The dense regions may thus localize membrane constituents that bind calcium. The results are discussed in relation to the role of calcium in control of cell-to-cell communication, intestinal calcium uptake, and the pyroantimonate technique for ion localization.
火焰光度法显示，常规用于电子显微镜的戊二醛和缓冲溶液含有不同量的钙。在各种组织中，与膜相邻的电子不透明沉积物的存在与固定剂中钙的存在相关。在昆虫肠道（中肠）中，沉积物出现在顶端和侧面质膜附近。这些沉积物在未经后渗透处理的戊二醛固定组织中尤为明显。如果在冲洗液和锇溶液中添加钙，在经锇处理的组织中也能观察到沉积物。使用无钙固定剂时没有沉积物，但添加痕量氯化钙（低至5×10⁻⁵M）时则会出现沉积物。沉积物沿着连接膜以规则间隔出现，提供的图像与其他使用焦锑酸盐试图定位钠的研究人员获得的图像惊人地相似。其他二价阳离子（Mg²⁺、Sr²⁺、Ba²⁺、Mn²⁺、Fe²⁺）似乎可以替代钙，而钠、钾、镧和汞则不能。在用添加了钙的锇进行后固定后，沉积物可解析为顶端和侧面质膜内小叶上的斑块。因此，致密区域可能定位了结合钙的膜成分。本文结合钙在控制细胞间通讯、肠道钙吸收以及焦锑酸盐离子定位技术中的作用对结果进行了讨论。
