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]aspartate release from synaptosomes and micro slices has been investigated. The rate of spontaneous efflux of the labeled amino acid from synaptosomes depended on the accumulation time of this compound and changed from 0.84 till 0.14 pmol/min per 1 mg protein for 2-30 minutes of incubation. The rate decreased to 0.11 +/- 0.01 pmol/min per 1 mg protein in 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 different 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 release 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 of D-[H-3]aspartate from slices was enhanced in the presence of 1 mM kainic acid in the incubation medium while the K+-simulated release of the amino acid was markedly inhibited and was about 43.5% of the control at a maximal superfusion rate. The ambivalent effect of kainic acid on spontaneous efflux of exogenous aspartate from synaptosomes and brain slices may be accounted for by the existence on the neurones of specific kainate receptors whose activation may contribute to an increases release of the amino acid, and by their absence on the synaptosomal membrane.