Heterodimeric amino acid transporters: expression of heavy but not light chains of CD98 correlates with induction of amino acid transport systems in human placental trophoblast.

1. Activity of amino acid transport and relative abundance of mRNAs encoding related transporters have been studied in parallel either before or following in vitro culture of explants of human placental chorionic villi. 2. Amino acid transport activities through systems L (1.9-fold), y+L (2.6-fold) and y+ (3.2-fold) were markedly enhanced following culture for 48 h. 3. Relative mRNA abundance (determined by reverse transcription-polymerase chain reaction) for the heavy chain of CD98 surface antigen and for the cationic amino acid transporter-1 were similarly stimulated (2.8-fold and 2.6-fold, respectively). In contrast, none of the mRNA levels for light chains of CD98 (system L-amino acid transporter-1, system L-amino acid transporter-2, system y+L-amino acid transporter-1 and system y+L-amino acid transporter-2) studied nor for the cationic amino acid transporter-2B were altered.