van der Ende A, du Maine A, Simmons C F, Schwartz A L, Strous G J
J Biol Chem. 1987 Jun 25;262(18):8910-6.
Growing human choriocarcinoma BeWo b24 cells contain 1.5 X 10(6) functional cell surface transferrin binding sites and 2.0 X 10(6) intracellular binding sites. These cells rapidly accumulate iron at a rate of 360,000 iron atoms/min/cell. During iron uptake the transferrin and its receptor recycle at least each 19 min. The accumulated iron is released from the BeWo cells at a considerable rate. The time required to release 50% of previously accumulated iron into the extracellular medium is 30 h. This release process is cell line-specific as HeLa cells release very little if any iron. The release of iron by BeWo cells is stimulated by exogenous chelators such as apotransferrin, diethylenetriaminepenta-acetic acid, desferral, and apolactoferrin. The time required to release 50% of the previously accumulated iron into medium supplemented with chelator is 15 h. In the absence of added chelators iron is released as a low molecular weight complex, whereas in the presence of chelator the iron is found complexed to the chelator. Uptake of iron is inhibited by 250 microM primaquine or 2.5 microM monensin. However, the release of iron is not inhibited by these drugs. Intracellular iron is stored bound to ferritin. A model for the release of iron by BeWo cells and its implication for transplacental iron transport is discussed.
生长中的人绒毛膜癌BeWo b24细胞含有1.5×10⁶个功能性细胞表面转铁蛋白结合位点和2.0×10⁶个细胞内结合位点。这些细胞以360,000个铁原子/分钟/细胞的速度快速积累铁。在铁摄取过程中，转铁蛋白及其受体至少每19分钟循环一次。积累的铁以相当快的速度从BeWo细胞中释放出来。将先前积累的铁的50%释放到细胞外培养基中所需的时间为30小时。这种释放过程具有细胞系特异性，因为HeLa细胞几乎不释放铁（如果有释放的话）。BeWo细胞释放铁受到外源性螯合剂如脱铁转铁蛋白、二乙烯三胺五乙酸、去铁胺和脱铁乳铁蛋白的刺激。将先前积累的铁的50%释放到添加了螯合剂的培养基中所需的时间为15小时。在没有添加螯合剂的情况下，铁以低分子量复合物的形式释放，而在有螯合剂存在的情况下，铁与螯合剂结合。250微摩尔的伯氨喹或2.5微摩尔的莫能菌素可抑制铁的摄取。然而，这些药物并不抑制铁的释放。细胞内的铁与铁蛋白结合储存。本文讨论了BeWo细胞释放铁的模型及其对胎盘铁转运的意义。
