Komazaki S, Takada M, Clark N B
Department of Anatomy, Saitama Medical School, Japan.
Anat Embryol (Berl). 1992 Dec;186(6):529-35. doi: 10.1007/BF00186975.
The chorioallantoic membrane (CAM) of the chick embryo actively transports calcium from the egg shell into the embryonic circulation. To investigate the intracellular pathway of calcium transport across the CAM, ultrastructural localization of intracellular calcium in cells of the chorionic ectoderm (CE) was determined using cytochemical methods and X-ray microanalysis. Treatment of the CE with potassium oxalate, potassium ferricyanide or potassium pyroantimonate revealed large numbers of electron-dense granules (EDGs) in the ectodermal cells. These measure 30-40 nm in diameter, and are not membrane-bound. These granules were seen in all three cell types of the CE. The presence of calcium in the EDG was directly confirmed by X-ray microanalysis. When strontium or barium ions were applied to the shell membrane side of the CAM, the cells of the CE incorporated these divalent cations and sequestered them in granules (25-40 nm in diameter) in cytoplasm and mitochondria. This study indicates that calcium enters the CE cells by means other than endocytosis, as the EDGs are not membrane-bound, that all three types of the CE cells appear to function in transport of calcium from shell to embryo during embryogenesis, and that the EDG plays important roles in intracellular accumulation of calcium during the process of calcium transport across the chorioallantoic membrane.
鸡胚的绒毛尿囊膜（CAM）能将蛋壳中的钙主动转运至胚胎循环系统。为了探究钙跨绒毛尿囊膜转运的细胞内途径，运用细胞化学方法和X射线微分析法对绒毛膜外胚层（CE）细胞内钙进行了超微结构定位。用草酸钾、铁氰化钾或焦锑酸钾处理CE后，在外胚层细胞中发现了大量电子致密颗粒（EDGs）。这些颗粒直径为30 - 40纳米，且无膜包裹。在CE的所有三种细胞类型中均可见到这些颗粒。通过X射线微分析法直接证实了EDG中存在钙。当将锶或钡离子施加于绒毛尿囊膜的壳膜侧时，CE细胞摄取了这些二价阳离子并将它们隔离在细胞质和线粒体中直径为25 - 40纳米的颗粒中。本研究表明，钙通过非内吞作用的方式进入CE细胞，因为EDG无膜包裹；在胚胎发育过程中，CE的所有三种细胞类型似乎都参与了从蛋壳到胚胎的钙转运；并且在钙跨绒毛尿囊膜转运过程中，EDG在细胞内钙积累中发挥着重要作用。
