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

We have investigatedL-arginine transport systems in the human placentalsyncytiotrophoblast across gestation using purified microvillous (MVM)and basal (BM) plasma membrane vesicles. In MVM from first-trimesterand term placentas, L-arginine transport was by systemsy⁺ and y⁺L. In BM (term placentas), however,there was evidence for system y⁺L only. The Michaelisconstant of system y⁺L was significantly lower (P < 0.05) in first-trimester compared with term MVM and lower in termMVM compared with BM (P < 0.05). There was no functionalevidence for system b⁰⁺ in term MVM or BM. Cationic aminoacid transporter (CAT) 1, CAT 4, and 4F2hc were detected using RT-PCRin placentas throughout gestation. rBAT was not detected in termplacentas. An ~85-kDa and an ~135-kDa protein was detected byWestern blotting in MVM under reducing and nonreducing conditions,respectively, consistent with the 4F2hc monomer and the 4F2hc-lightchain dimer, and their expression was significantly higher (P < 0.05) in term compared with first-trimester MVM. These proteinswere not detected in BM despite functional evidence for systemy⁺L. These data suggest different roles for 4F2hc in thedevelopment and polarization of cationic amino acid transporters in the syncytiotrophoblast.