Characterization of a Cell Line Model for d-Serine Uptake.

d-Serine is an important co-agonist of the N-methyl-d-aspartate (NMDA) receptors in the brain and its altered activity was identified in various pathological conditions. Modification of the extracellular d-serine level is suggested to be able to modulate the receptor function. Its transporters may thus serve as potential drug targets. The aim of this work was to find an easily available human cell line model appropriate for screening molecules affecting d-serine transporters. Characteristics of d-serine transport into SH-SY5Y human neuroblastoma cell line were studied and compared to those in cultured primary astrocytes. Uptake was followed by measuring intracellular d-serine concentration by capillary electrophoresis with laser induced fluorescence detection method. We found that SH-SY5Y cells express functional ASCT-1 and ASCT-2 neutral amino acid transporters and show similar d-serine uptake kinetics to cultured astrocytes. Neutral amino acids inhibited d-serine uptake similarly in both cell types. Complete inhibition was achieved by l-alanine and l-threonine alike, while the two-step inhibition curve of trans-hydroxy-l-proline, a selective inhibitor of ASCT-1 supported the presence of functioning ASCT-1 and ASCT-2 transporters. Its higher affinity step corresponding to inhibition of ASCT-1 was responsible for about 30% of the total d-serine uptake. Based on our results human SH-SY5Y cell line shows similar uptake characteristics to primary astrocytes and thus can serve as a suitable model system for testing of compounds for influencing d-serine uptake into astrocytes.