Sodium-independent lysine uptake by the bewo choriocarcinoma cell line

Abstract

Transport of L-lysine by a cultured placental trophoblast cell line was investigated by characterization of L-[ 3H]lysine uptake. In the mononuclear form of the BeWo clone b30 choriocarcinoma cell, at least two sodium-independent systems are present. Concentration dependence data were fitted by a two system model with K m values ( ± s.e.) of 2 ± 0.7 and 94 ± 31 μ m and V max values ( ± s.e.) of 0.7 ± 0.3 and 25 ± 6.0 n m/mg DNA/min. A portion of sodium-independent uptake was inhibited by the sulphydryl modifying reagent N-ethylmaleimide (NEM). Following NEM treatment, the data were fitted by a single system with K m=10±2 μ m and V max=5.1 ± 0.8 n m/ mg DNA/min. In the absence of sodium, NEM-resistant uptake was sensitively inhibited by leucine whereas NEM-sensitive uptake was not inhibited by leucine. It is concluded that like placental basal membrane, the mononuclear BeWo cell possesses two sodium-independent L-lysine transport systems. The high-capacity, NEM-sensitive, leucine-insensitive system resembles the widespread system y+. The high-affinity, NEM-resistant, leucine-sensitive system resembles system b 0,+.