ACTION OF KAINIC ACID ON THE RELEASE OF D -[H-3]ASPARTATE FROM SYNAPTOSOMES AND RAT-BRAIN CORTICAL SLICES

Action of kainic acid-a neurotoxic analog of glutamate on D-[H-3]aspar tate release from synaptosomes and micro slices has been investigated. The rate of spontaneous efflux of the labeled amino acid from synapto somes depended on the accumulation time of this compound and changed f rom 0.84 till 0.14 pmol/min per 1 mg protein for 2-30 minutes of incub ation. The rate decreased to 0.11 +/- 0.01 pmol/min per 1 mg protein i n the presence of 0.5 mM kainic acid and was the same for each case of accumulation. The release of D-[H-3]aspartate accumulated under diffe rent concentrations of the amino acid but constant time was inhibited in the presence of 0.5 kainate by 26.2 +/- 2.4% of control. The releas e of D-[H-3]aspartate accumulated by micro slices has been studied at superfusion rates of 0.5-1.6 ml/min. The rate of spontaneous release o f D-[H-3]aspartate from slices was enhanced in the presence of 1 mM ka inic acid in the incubation medium while the K+-simulated release of t he amino acid was markedly inhibited and was about 43.5% of the contro l at a maximal superfusion rate. The ambivalent effect of kainic acid on spontaneous efflux of exogenous aspartate from synaptosomes and bra in slices may be accounted for by the existence on the neurones of spe cific kainate receptors whose activation may contribute to an increase s release of the amino acid, and by their absence on the synaptosomal membrane.