Fisher G J, Kelley L K, Smith C H
Am J Physiol. 1987 Jan;252(1 Pt 1):C38-46. doi: 10.1152/ajpcell.1987.252.1.C38.
As a first step in understanding the cellular basis of maternal-fetal calcium transfer, we examined the characteristics of calcium uptake by a highly purified preparation of the syncytiotrophoblast basal (fetal facing) plasma membrane. In the presence of nanomolar concentrations of free calcium, basal membranes demonstrated substantial ATP-dependent calcium uptake [K0.5 = 119 nM, maximum velocity (Vmax) = 2 nM X min-1 X mg-1]. This uptake required magnesium, was not significantly affected by Na+ or K+ (50 mM), or sodium azide (10 mM). Intravesicular calcium was rapidly and completely released by the calcium ionophore A23187. Calcium transport was significantly stimulated by the calcium-dependent regulatory protein calmodulin. Placental membrane fractions enriched in endoplasmic reticulum (ER) and mitochondria also demonstrated ATP-dependent calcium uptake. In contrast to basal membrane, mitochondrial calcium uptake was completely inhibited by azide. The rate of calcium uptake by the ER was only 20% of that of basal membranes. We conclude that the placental basal plasma membrane possesses a high-affinity calcium transport system similar to that found in plasma membranes of a variety of cell types. This transporter is situated to permit it to function in vivo in maternal-fetal calcium transfer.
作为理解母胎钙转运细胞基础的第一步，我们检测了高度纯化的合体滋养层基底（面向胎儿）质膜的钙摄取特性。在纳摩尔浓度的游离钙存在下，基底膜表现出大量的ATP依赖性钙摄取[半最大效应浓度（K0.5）=119 nM，最大速度（Vmax）=2 nM·min-1·mg-1]。这种摄取需要镁，不受Na+或K+（50 mM）或叠氮化钠（10 mM）的显著影响。钙离子载体A23187可迅速且完全释放囊泡内的钙。钙转运受到钙依赖性调节蛋白钙调蛋白的显著刺激。富含内质网（ER）和线粒体的胎盘膜组分也表现出ATP依赖性钙摄取。与基底膜不同，线粒体钙摄取被叠氮化钠完全抑制。内质网的钙摄取速率仅为基底膜的20%。我们得出结论，胎盘基底质膜拥有一种高亲和力钙转运系统，类似于在多种细胞类型的质膜中发现的系统。这种转运体的位置使其能够在母胎钙转运的体内过程中发挥作用。
