Novak D A, Matthews J C, Beveridge M J, Yao S Y, Young J, Kilberg M S
Department of Pediatrics, University of Florida College of Medicine, USA.
Placenta. 1997 Nov;18(8):643-8. doi: 10.1016/s0143-4004(97)90005-9.
Na(+)-independent cationic amino acid transport in the rat placenta occurs by leucine-sensitive and leucine-insensitive pathways. The ontogeny of these transport mechanisms within the rat placenta has been described recently. To assign the leucine-inhibitable portion of uptake definitively the uptake of [3H]arginine was studied in the presence of both BCH (to inhibit system Bo,+) and varied concentrations of leucine. Uptake of arginine into basal-enriched membrane vesicles derived from rat placenta was, in the presence of sodium, inhibited by micromolar concentrations of leucine, consistent with assignment of this activity to system y+L. In contrast, the majority of arginine uptake into apical-enriched membrane vesicles was leucine insensitive. Messenger RNA derived from rat placenta at days 14, 16, 18 and 20 of gestation was hybridized with full-length rat cDNA probes against NBAT and 4F2HC (thought to encode proteins associated with system bo,+ and y+L activities, respectively). No NBAT mRNA was detected, whereas 4F2HC mRNA was present at all gestational stages, increasing 12-fold over the last third of gestation. It is concluded that system y+L is present in the basal plasma membrane of the rat placenta syncytium and is subject to developmental regulation by a mechanism that alters the steady content of 4F2HC mRNA.
大鼠胎盘内不依赖钠离子的阳离子氨基酸转运通过亮氨酸敏感和亮氨酸不敏感途径进行。这些转运机制在大鼠胎盘内的个体发生情况最近已有描述。为明确摄取中亮氨酸可抑制部分的性质，在同时存在BCH（抑制系统Bo,+）和不同浓度亮氨酸的情况下研究了[3H]精氨酸的摄取。在有钠离子存在时，源自大鼠胎盘的富含基底膜囊泡对精氨酸的摄取受到微摩尔浓度亮氨酸的抑制，这与将该活性归属于系统y+L一致。相反，大部分精氨酸摄取到富含顶端膜囊泡中对亮氨酸不敏感。在妊娠第14、16、18和20天取自大鼠胎盘的信使核糖核酸与针对NBAT和4F2HC的大鼠全长互补脱氧核糖核酸探针杂交（分别被认为编码与系统bo,+和y+L活性相关的蛋白质）。未检测到NBAT信使核糖核酸，而4F2HC信使核糖核酸在所有妊娠阶段均存在，在妊娠最后三分之一期间增加了12倍。结论是系统y+L存在于大鼠胎盘合体滋养层的基底质膜中，并受一种改变4F2HC信使核糖核酸稳定含量的机制的发育调控。
