Fig 1. Transport of [³H]D-serine and [³H]L-serine by rat hippocampal astrocyte cultures.

Transport was conducted as described in Materials and Methods. (A,B) Transport of [³H]D-serine (A) or [³H]L-serine (B) over a range of substrate concentrations in the presence and absence of sodium. Data are from a single experiment that was repeated an additional 2 times for [³H]D-serine and 7 times for [³H]L-serine. Curves were fitted using GraphPad Prism (see Table 1 for mean K_m and V_max values). The sodium-dependent transport was calculated by subtracting transport in the presence of sodium from that in buffer where sodium was replaced by equimolar choline. (C,D) Dependence of [³H]D-serine (C) or [³H]L-serine (D) transport on extracellular sodium. Experiments were conducted in sodium-containing (Total) or choline chloride-containing (zero Na) buffer at a substrate concentration of 0.5 μM. For [³H]D-serine transport n = 3, for [³H]L-serine transport n = 12.