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 [ 3 H] D ‐aspartate from reaggregate cultures (retinospheroids) or from monolayer cultures of chick retinal cells, respectively. Kainate increased the fluorescence ratio of the Na + indicator SBFI and stimulated a dose‐dependent release of glutamate in low (0.1 mM) Ca 2+ medium, as measured using a fluorometric assay. Under the same experimental conditions, the release evoked by N‐methyl‐ D ‐aspartate (NMDA; 400 μM) was about half of that evoked by the same kainate concentration; α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxasolepropionic acid (AMPA; 400 μM) did not trigger a significant response. In the presence of 1 mM CaCl 2 , all of the agonists increased the [Ca 2+ ] i , as determined with the fluorescence dye Indo‐1, but the glutamate release evoked by NMDA and kainate was significantly lower than that measured in 0.1 mM CaCl 2 medium. Inhibition by Ca 2+ of the kainate‐stimulated release of glutamate was partially reversed by the phospholipase A 2 inhibitor oleiloxyethyl phosphorylcholine (OPC), suggesting that the effect was mediated by the release of arachidonic acid, which inhibits the glutamate carrier. Accordingly, kainate, NMDA, and AMPA stimulated a Ca 2+ ‐dependent release of [ 3 H]arachidonic acid, and the direct addition of the exogenous fatty acid to the medium decreased the release of glutamate evoked by kainate in low (0.1 mM) CaCl 2 medium. In monolayer cultures, we showed that NMDA, kainate, and AMPA also stimulated the release of [ 3 H] D ‐aspartate, but in this case release in the presence of 1 mM CaCl 2 was significantly higher than that evoked in media with no added Ca 2+ . The ranking order of efficacy for stimulation of Ca 2+ ‐dependent release of [ 3 H] D ‐aspartate was NMDA ≪ kainate < AMPA. © 1996 Wiley‐Liss, Inc.