Development and polarization of cationic amino acid transporters and regulators in the human placenta

Academic Unit of Child Health, University of Manchester and Department of Obstetrics and Gynecology, St. Mary's Hospital, Manchester M13 0JH, United Kingdom We have investigated L -arginine transport systems in the human placental syncytiotrophoblast across gestation using purified microvillous (MVM) and basal (BM) plasma membrane vesicles. In MVM from first-trimester and term placentas, L -arginine transport was by systems y + and y + L. In BM (term placentas), however, there was evidence for system y + L only. The Michaelis constant of system y + L was significantly lower ( P