Matthews J C, Beveridge M J, Malandro M S, Rothstein J D, Campbell-Thompson M, Verlander J W, Kilberg M S, Novak D A
Department of Pediatrics, University of Florida College of Medicine, Gainesville 32610, USA.
Am J Physiol. 1998 Mar;274(3):C603-14. doi: 10.1152/ajpcell.1998.274.3.C603.
Concentrative absorption of glutamate by the developing placenta is critical for proper fetal development. The expression of GLAST1, GLT1, EAAC1, and EAAT4, known to be capable of D-aspartate-inhibitable and Na(+)-coupled glutamate transport (system X-AG), was evaluated in day 14 vs. day 20 rat chorioallantoic placenta. Steady-state mRNA levels were greater at day 20 for all transporters. Immunohistochemistry determined that the expression of GLAST1, GLT1, and EAAC1 was greater throughout the day 20 placenta and was asymmetric with respect to cellular localization. EAAT4 protein was not detected. System X-AG activity was responsible for most of the Na(+)-dependent glutamate uptake and was greater in day 20 than in day 14 apical and basal membrane subdomains of the labyrinth syncytiotrophoblast. Greater quantities of EAAC1 and GLAST1 protein were identified on day 20, and quantities were greater in basal than in apical membranes. GLT1 expression, unchanged in apical membranes, was decreased in basal membranes. These data correlate transporter mRNA and protein content with transport activity and demonstrate an increasing capacity for glutamate absorption by the developing placenta.
发育中的胎盘对谷氨酸的浓缩吸收对胎儿的正常发育至关重要。已知GLAST1、GLT1、EAAC1和EAAT4能够进行D-天冬氨酸抑制和Na(+)偶联的谷氨酸转运（X-AG系统），在第14天和第20天的大鼠绒毛尿囊胎盘对其表达进行了评估。所有转运体在第20天的稳态mRNA水平更高。免疫组织化学测定显示，GLAST1、GLT1和EAAC1在整个第20天的胎盘表达更高，并且在细胞定位方面不对称。未检测到EAAT4蛋白。X-AG系统活性负责大部分Na(+)依赖性谷氨酸摄取，并且在第20天比第14天的迷路合体滋养层顶端和基底膜亚结构域中的活性更高。在第20天鉴定出更多量的EAAC1和GLAST1蛋白，并且基底膜中的量比顶端膜中的量更多。GLT1在顶端膜中的表达未改变，而在基底膜中表达降低。这些数据将转运体mRNA和蛋白含量与转运活性相关联，并证明发育中的胎盘对谷氨酸的吸收能力不断增强。
