GLUTAMATE RELEASE EVOKED BY GLUTAMATE-RECEPTOR AGONISTS IN CULTURED CHICK RETINA CELLS - MODULATION BY ARACHIDONIC-ACID

We studied the effect of ionotropic glutamate receptor agonists on the release of endogenous glutamate or of [H-3]D-aspartate from reaggrega te cultures (retinospheroids) or from monolayer cultures of chick reti nal cells, respectively, Kainate increased the fluorescence ratio of t he Naf indicator SBFI and stimulated a dose-dependent release of gluta mate in low (0.1 mM) Ca2+ medium, as measured using a fluorometric ass ay, Under the same experimental conditions, the release evoked by N-me thyl-D-aspartate (NMDA; 400 mu M) was about half of that evoked by the same kainate concentration; lpha-amino-3-hydroxy-5-methyl-4-isoxasole propionic acid (AMPA; 400 mu M) did not trigger a significant response , In the presence of 1 mM CaCl2, all of the agonists increased the [Ca 2+](i), as determined with the fluorescence dye Indo-1, but the glutam ate release evoked by NMDA and kainate was significantly lower than th at measured in 0.1 mM CaCl2 medium. Inhibition by Ca2+ of the kainate- stimulated release of glutamate was partially reversed by the phosphol ipase A(2) inhibitor oleiloxyethyl phosphorylcholine (OPC), suggesting that the effect was mediated by the release of arachidonic acid, whic h inhibits the glutamate carrier, Accordingly, kainate, NMDA, and AMPA stimulated a Ca2+-dependent release of [H-3]arachidonic acid, and the direct addition of the exogenous fatty acid to the medium decreased t he release of glutamate evoked by kainate in low (0.1 mM) CaCl2 medium . In monolayer cultures, we showed that NMDA, kainate, and AMPA also s timulated the release of [H-3]D-aspartate, but in this case release in the presence of 1 mM CaCl2 was significantly higher than that evoked in media with no added Ca2+. The ranking order of efficacy for stimula tion of Ca2+-dependent release of [H-3]D-aspartate was NMDA much great er than kainate>AMPA. (C) 1996 Wiley-Liss, Inc.