Characterization of choline transport at maternal and fetal interfaces of the perfused guinea‐pig placenta.
Characterization of choline transport at maternal and fetal interfaces of the perfused guinea‐pig placenta.
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灌注豚鼠胎盘母体和胎儿界面胆碱转运的表征。
DOI：
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发表时间：
1985
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影响因子：
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通讯作者：
D. Yudilevich
中科院分区：
文献类型：
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作者：
J. Sweiry;D. Yudilevich
用单循环配对示踪剂(细胞外参照和试验底物)稀释法研究了胆碱在合体滋养层细胞中的单向流入和流出。细胞摄取0.05mM的[~3H]胆碱在母体和胎儿一侧分别为51+/-2和49+/-2。单向流入(0.05-4.0 mM-胆碱)的动力学表明，两侧存在饱和和非饱和成分：母胎界面的Km(Mm)值分别为0.12和0.13，Vmax(Mumol min-1g-1)值分别为0.08和0.07，表观线性转移常数(min-1g-1)分别为0.11和0.12。[~3H]胆碱从胎盘流出回同侧循环(回流)通常很快(5-6分钟内20-60%)且不对称，胎儿与母体的比率通常在1以上。根据对侧循环收集5-6分钟(0.05 mM-胆碱)，在双向注射示踪剂后，观察到在双侧灌流的胎盘中，经胎盘的特异性胆碱转移很小(小于注射剂量的10%)。当示踪剂从两个循环中注射时，胎盘在5-6分钟结束时[~3H]胆碱的滞留约为注射剂量的25%。胆碱类似物如半胱氨酸-3、硫胺、乙醇胺和N，N-二甲基乙醇胺可抑制胆碱的单向内流，而甜菜碱和乙酸酯则不起作用。缺乏正常钠梯度(灌流液中的钠被Tris或锂取代)并不抑制胆碱的转运。代谢抑制剂二硝基苯酚(1.0 mM)和氰化钾(1.0 mM)基本上无效(长达40分钟的灌流)。与之相比，N-乙基马来酰亚胺对[~3H]胆碱回流的影响明显加快，导致胎盘对标记物的净摄取显著减少。我们的发现表明，在生理血液浓度下，胆碱进入胎盘是一个由载体介导的快速过程，发生在滋养细胞的母体和胎儿一侧。这种细胞摄取可能与乙酰胆碱的合成有关，已知乙酰胆碱存在于人类胎盘组织中。在我们的实验条件下，胆碱通过胎盘的特异性转移是一个非常缓慢的过程，这与观察到的滋养层细胞的快速和高摄取形成了鲜明对比。
Unidirectional influx and efflux of choline into the syncytiotrophoblast were investigated from both maternal and fetal circulations of the perfused guinea‐pig placenta by using a single‐circulation paired‐tracer (extracellular reference and test substrate) dilution technique. Cellular uptake of [3H]choline at 0.05 mM was (mean percentage +/‐ S.E. of mean, n = 14 placentae) 51 +/‐ 2 and 49 +/‐ 2, on maternal and fetal sides, respectively. Kinetics of unidirectional influx (0.05‐4.0 mM‐choline) indicated the existence of saturable and non‐saturable components on both sides: on maternal and fetal interfaces the Km (mM) values were respectively, 0.12 and 0.13, the Vmax (mumol min‐1 g‐1) values, 0.08 and 0.07 and the apparent linear transfer constants (min‐1 g‐1) 0.11 and 0.12. Efflux of [3H]choline from the placenta back into the ipsilateral circulation (backflux) was generally fast (20‐60% in 5‐6 min) and asymmetric with the fetal: maternal ratio usually above unity. Transplacental specific choline transfer in the dually perfused placenta, when observed, was small (less than 10% of the injected dose) following tracer injections in either direction based on the 5‐6 min collection of the contralateral circulation (at 0.05 mM‐choline). Placental retention of [3H]choline at the end of the 5‐6 min period was about 25% of the injected dose when the tracers were injected from either circulation. Analogues of choline such as hemicholinium‐3, thiamine, ethanolamine and N,N‐dimethylethanolamine inhibited choline unidirectional influx, whereas betaine and acetate had no effect. The absence of the normal sodium gradient (perfusate sodium was replaced by Tris or by lithium) did not inhibit choline transport. The metabolic inhibitors dinitrophenol (1.0 mM) and potassium cyanide (1.0 mM) were essentially ineffective (up to 40 min perfusion). The sulphydryl reagent N‐ethylmaleimide did not appear to inhibit the influx, in comparison with its effect on [3H]choline backflux which was greatly accelerated, resulting in a dramatic reduction in placental net uptake of the label. Our findings show that choline transport into the placenta is a rapid carrier‐mediated process occurring at both maternal and fetal sides of the trophoblast, at physiological blood concentrations. This cellular uptake is possibly related to the synthesis of acetylcholine, which is known to occur in human placental tissue. Specific transplacental transfer of choline was a very slow process under the conditions of our experiments and this contrasted with the observed fast and high uptake into the trophoblast.