Hoeltzli S D, Smith C H
Edward Mallinckrodt Department of Pediatrics, Washington University School of Medicine, Children's Hospital, St. Louis, Missouri 63110.
Am J Physiol. 1989 Mar;256(3 Pt 1):C630-7. doi: 10.1152/ajpcell.1989.256.3.C630.
Concentrative transfer of amino acids from mother to fetus is affected by transport across both microvillous (maternal-facing) and basal (fetal-facing) plasma membranes of the human placental syncytiotrophoblast. Isolated basal plasma membrane vesicles were used to elucidate transport systems for neutral amino acids across this membrane. The concentration dependence and inhibition of zero-trans-alanine uptake were studied and four pathways for alanine uptake were defined as follows: 1) a sodium-dependent system shared by methylaminoisobutyric acid, which has the characteristics of an A system; 2) a sodium-dependent system resistant to inhibition by methylaminoisobutyric acid, which has the characteristics of an ASC system; 3) a sodium-independent system which may resemble an L system; 4) nonsaturable uptake. The microvillous membrane of the syncytiotrophoblast possesses systems similar to 1 and 3, but system 2 is unique to the basal plasma membrane. Active and passive transport of amino acids across both microvillous and basal plasma membranes may contribute to trophoblast amino acid uptake and nutrition and to the transfer of amino acids to the fetus.
氨基酸从母体到胎儿的浓缩转运受到人类胎盘合体滋养层微绒毛（面向母体）和基底（面向胎儿）质膜转运的影响。分离的基底质膜囊泡用于阐明中性氨基酸跨此膜的转运系统。研究了零转运丙氨酸摄取的浓度依赖性和抑制作用，并确定了丙氨酸摄取的四条途径如下：1）一种由甲氨基异丁酸共用的钠依赖性系统，具有A系统的特征；2）一种对甲氨基异丁酸抑制有抗性的钠依赖性系统，具有ASC系统的特征；3）一种可能类似于L系统的钠非依赖性系统；4）非饱和摄取。合体滋养层的微绒毛膜具有与1和3类似的系统，但系统2是基底质膜特有的。氨基酸跨微绒毛和基底质膜的主动和被动转运可能有助于滋养层氨基酸摄取和营养以及氨基酸向胎儿的转运。
