Taurine transporter in fetal T lymphocytes and platelets: differential expression and functional activity

Transplacental transfer of taurine, a beta-amino acid essential for fetal and neonatal development, constitutes the primary source of taurine for the fetus. Placental transport of taurine is compromised in pregnancies complicated by intrauterine growth restriction, resulting in a reduced concentration of taurine in cord plasma. This could impact on fetal cellular metabolism as taurine represents the most abundant intracellular amino acid in many fetal cell types. In the present study, we have used pure isolates of fetal platelets and T lymphocytes from cord blood of placentas, from normal, term pregnancies, as fetal cell types to examine the cellular uptake mechanisms for taurine by the system beta transporter and have compared gene and protein expression for the taurine transporter protein (TAUT) in these two cell types. System beta activity in fetal platelets was 15-fold higher compared with fetal T lymphocytes (P < 0.005), mirroring greater TAUT mRNA expression in platelets than T lymphocytes (P < 0.005). Cell-specific differences in TAUT protein moieties were detected with a doublet of 75 and 80 kDa in fetal platelets compared with 114 and 120 kDa in fetal T lymphocytes, with relatively higher expression in platelets. We conclude that greater system beta activity in fetal platelets compared with T lymphocytes is the result of relatively greater TAUT mRNA and protein expression. This study represents the first characterization of amino acid transporters in fetal T lymphocytes.