d-Serine uptake by isolated retinas is consistent with ASCT-mediated transport

Uptake of the neuromodulator d-serine by isolated larval tiger salamander (Ambystoma tigrinum) retinas was measured using capillary electrophoresis (CE). Excised retinas were incubated in Ringer's solution in the presence of 5 μM d-serine. The supernatant was removed after 30 min, mixed with 4-fluoro-7-nitrobenz-2-oxa-1,3-diazole (NBD-F) to fluorescently label amines and analyzed using CE. Significant d-serine uptake was observed over a period of 1.5 h. This is the first observation of d-serine uptake by an intact retinal tissue. d-Serine uptake in the retina was Na+-dependent and blocked by l-alanine, l-threonine, and l-cysteine. This pharmacology is consistent with the sodium dependent heteroexchange expected of system ASC-type transporters.