Abstract
The effects of gabapentin (GBP) and (S)-pregabalin (PGB) on the intracellular concentrations of d-serine and the expression of serine racemase (SR) in PC-12 cells were determined. Intracellular d-serine concentrations were determined using an enantioselective capillary electrophoresis assay with laser-induced fluorescence detection. Increasing concentrations of GBP, 0.1-20μM, produced a significant decrease in d-serine concentration relative to control, 22.9±6.7% at 20μM (*p<0.05), with an IC(50) value of 3.40±0.29μM. Increasing concentrations of PGB, 0.1-10μM, produced a significant decrease in d-serine concentration relative to control, 25.3±7.6% at 10μM (*p<0.05), with an IC(50) value of 3.38±0.21μM. The compounds had no effect on the expression of monomeric-SR or dimeric-SR as determined by Western blotting. The results suggest that incubation of PC-12 cells with GBP and PGB reduced the basal activity of SR, which is most likely a result of the decreased Ca(2+) flux produced via interaction of the drugs with the α(2)-δ subunit of voltage-gated calcium channels. d-Serine is a co-agonist of the N-methyl d-aspartate receptor (NMDAR) and reduced d-serine concentrations have been associated with reduced NMDAR activity. Thus, GBP and PGB may act as indirect antagonists of NMDAR, a mechanism that may contribute to the clinical effects of the drugs in neuropathic pain.