van Dijk J P, van der Zande F G, Kroos M J, Starreveld J S, van Eijk H G
Erasmus University Rotterdam, Department of Chemical Pathology, The Netherlands.
J Dev Physiol. 1993 May;19(5):221-6.
Transferrin receptors (TfR's) on the syncytiotrophoblast mediate transferrin (Tf) dependent Fe uptake and transfer to the fetus. We studied TfR number and density at the microvillous membrane isolated from guinea pig placentas at day 40, 50 and 64 (near term), together with the K(a) values for the main serum isotransferrins being biantennary Tf(slow) and triantennary Tf(fast). The effect of desialylation of either the microvillous membranes or of Tf(slow) and Tf(fast) on the binding characteristics was also studied. The number of TfR's per mg placenta- or membrane protein increased significantly from day 40 to term (P < 0.01 resp. P < 0.025). The K(a) values for Tf(slow) and Tf(fast) did not change during pregnancy. K(a)Tf(slow) = 0.3 nM-1, K(a)Tf(fast) = 0.19 nM-1 (P < 0.01). It is suggested that the increase in F(e) transfer during pregnancy is directly related to number and density of the TfR's at the syncytial border, and that adaptive adjustment of K(a) values does not play a role in the maturation of the transfer process. The pregnancy dependent shift to iso-transferrins with a higher degree of glycosylation offers no explanation for the increase of F(e) transfer during pregnancy. Desialylation of the microvillous membranes did not effect the binding parameters of Tf(slow) and Tf(fast), unless desialylation surpassed the 50% level. Then Ka values decreased and TfR number increased (P < 0.05). Desialylation of Tf(slow) and Tf(fast) had no effect on K(a) nor on the number of TfR. The maternal fetal interface therefore lacks an asialo-glycoprotein receptor.
合体滋养层上的转铁蛋白受体（TfR）介导转铁蛋白（Tf）依赖的铁摄取并将其转运至胎儿。我们研究了妊娠第40天、50天和64天（接近足月）从豚鼠胎盘分离的微绒毛膜上的TfR数量和密度，以及主要血清同种转铁蛋白（双天线Tf（慢型）和三天线Tf（快型））的解离常数（K(a)）值。还研究了微绒毛膜或Tf（慢型）和Tf（快型）去唾液酸化对结合特性的影响。每毫克胎盘或膜蛋白的TfR数量从第40天到足月显著增加（分别为P < 0.01和P < 0.025）。妊娠期间Tf（慢型）和Tf（快型）的K(a)值没有变化。K(a)Tf（慢型）= 0.3 nM-1，K(a)Tf（快型）= 0.19 nM-1（P < 0.01）。提示妊娠期间铁转运的增加与合体滋养层边界处TfR的数量和密度直接相关，且K(a)值的适应性调节在转运过程成熟中不起作用。妊娠时向糖基化程度更高的同种转铁蛋白的转变无法解释妊娠期间铁转运的增加。微绒毛膜去唾液酸化不影响Tf（慢型）和Tf（快型）的结合参数，除非去唾液酸化超过50%水平。此时Ka值降低且TfR数量增加（P < 0.05）。Tf（慢型）和Tf（快型）去唾液酸化对K(a)值和TfR数量均无影响。因此，母胎界面缺乏去唾液酸糖蛋白受体。
