Komazaki S, Takada M, Clark N B
Department of Anatomy, Saitama Medical School, Japan.
Anat Embryol (Berl). 1993 Jun;187(6):607-14. doi: 10.1007/BF00214440.
The yolk sac membrane (YSM) of the chick embryo transports calcium from the yolk into the embryonic circulation during the first half of development, but the intracellular pathway of calcium transport is poorly understood. In the present study, the ultrastructural localization of calcium was investigated in cells of the YSM of 9-day chick embryos. X-ray microanalysis as well as cytochemical techniques performed on yolk sac membrane cells treated with potassium oxalate, potassium ferricyanide and potassium antimonate demonstrated accumulation of calcium in yolk granules, digested yolk products, electron-dense bodies (EDBs; 100-400 nm diameter) and electron-dense granules (EDGs; 30-50 nm diameter). When strontium ions were injected into the yolk, they were incorporated into the endodermal cells and sequestered specifically in EDGs. From these results, we propose that calcium enters the endodermal cells by endocytosis of calcium-containing yolk granules, as well as through calcium channels in the apical cell membrane. In the cytoplasm, digested yolk products, EDBs, and EDGs act as sites of sequestration and accumulation of calcium. Extrusion of intracellular calcium into the extracellular space and embryonic circulation is accomplished by exocytosis of calcium-containing material and via an ion pump in the basal cell membrane.
在发育的前半期，鸡胚的卵黄囊膜（YSM）将钙从卵黄转运至胚胎循环，但钙转运的细胞内途径尚不清楚。在本研究中，对9日龄鸡胚YSM细胞中的钙进行了超微结构定位研究。对用草酸钾、铁氰化钾和锑酸钾处理的卵黄囊膜细胞进行X射线微分析和细胞化学技术分析，结果表明钙在卵黄颗粒、消化后的卵黄产物、电子致密体（EDB；直径100 - 400 nm）和电子致密颗粒（EDG；直径30 - 50 nm）中积累。当将锶离子注入卵黄时，它们被内胚层细胞摄取并特异性地隔离在EDG中。根据这些结果，我们提出钙通过含钙卵黄颗粒的内吞作用以及通过顶端细胞膜上的钙通道进入内胚层细胞。在细胞质中，消化后的卵黄产物、EDB和EDG作为钙隔离和积累的位点。细胞内钙向细胞外空间和胚胎循环的排出是通过含钙物质的胞吐作用以及通过基底细胞膜上的离子泵来完成的。
