| Abstract No.: | B-B2024 |
| Country: | Canada |
| | |
| Title: | GLUTAMATERGIC-INDUCED INCREASES OF INTRACELLULAR CALCIUM ARE ENHANCED BY D-SERINE IN RAT RETINAL GANGLION CELLS |
| | |
| Authors/Affiliations: | 1 Bryan Daniels*; 1 Janette Nason; 1 William Baldridge;
1 Dalhousie University, Halifsx, NS, Canada
|
| | |
| Content: | Objectives: It is well documented that glutamatergic activation of NMDA receptors is enhanced by glycine at a separate binding site. This co-agonist binding site can also be endogenously occupied by D-serine in the retina and elsewhere in the central nervous system. Previous work has shown a role for D-serine in the modulation of post-synaptic NMDA currents. One of the major functions of most NMDA channels is to permit calcium influx into cells. Therefore, we have investigated whether D-serine will also enhance glutamatergic-induced intracellular calcium [Ca2+]i increases in vitro and in situ.
Materials & Methods: Calcium imaging of immunopanned retinal ganglion cells (RGCs; P6-8 Long Evans rats) and RGCs in adult whole mount retinas was performed. Isolated RGCs were loaded with fura-2 AM calcium indicator dye and RGCs in the whole mount retinas were loaded with fura dextran. All experiments were performed in Mg2+ free conditions.
Results: Application of 10 µM glutamate was enhanced by co-exposure to D-serine in a dose dependant manner. D-Serine concentrations ≥ 1 µM increased the glutamate-induced [Ca2+]i response (mean±sd; 1 µM, 118±84 %; 10 µM, 282±273 %; 100 µM, 425±490 %). The peak effect of D-serine was seen at 100 µM since 1000 µM showed no further enhancement. At 10 µM, glycine or D-serine enhanced 10 µM glutamate-induced [Ca2+]i increases to similar levels (379±231 %, 474±422 % respectively). This effect was partially blocked by the NMDA co-agonist binding site antagonist 1-aminocyclobutane-1-carboxylic acid (ACBC; 100 µM).
In whole mount retinas [Ca2+]i responses to 200 µM NMDA showed no change with the co-application of 100 µM glycine or D-serine. Endogenous D-serine was degraded by a 10 min exposure to D-amino acid oxidase (DAAO; 200 µg/ml). Subsequent NMDA-induced [Ca2+]i increases were significantly reduced to 59±20 % of the response to NMDA prior to DAAO application in most RGCs. The calcium response to NMDA was recovered by the addition of 500 µM D-serine to 103±35% of the original response.
Conclusions: D-serine is at least as effective as glycine in its ability to enhance glutamatergic-induced increases of [Ca2+]i. It is capable of modulating [Ca2+]i over a range of concentrations in vitro. In situ, D-serine had no additive effect to increase [Ca2+]i possibly due to saturation of the NMDA receptor co-agonist binding site. Consistent with this hypothesis, enzymatic degradation of D-serine resulted in a reduction in the NMDA-induced [Ca2+]i response that was recovered by the exogenous application of D-serine.
|
| | |
| Back |
|
