Characterization of [ l- 3H]aspartate binding to chick retinal subcellular fractions

Binding of [ l- 3H]aspartate to synaptic receptors was examined in membranes from whole chick retina and subcellular fractions enriched with photoreceptor terminals (P 1) or terminals from the inner plexiform layer (P 2). Na +-independent, stereospecific, high affinity binding was concentrated in the P 1 fraction ( K b = 40nM ). P 2 fraction also showed a high affinity binding system ( K B = 11.8nM ) with lower capacity than in the P 1 fraction. Comparative studies with [ l-H 3]-asparate, [ l-H 3]-glutamate and [H 3]-kainate showed that l-aspartate and l-glutamate are the most potent inhibitors of the binding of the three ligands. Aspartate and glutamate binding were effectively displaced by N-methyl- dl-aspartate and α-amino adipate, whereas only [H 3]-glutamate binding was significantly inhibited by glutamatediethyl-ester. Kainic acid exhibited negligible affinity for aspartate and glutamate binding sites. Results indicate the presence of different receptors for glutamate and aspartate in both plexiform layers of the retina.