THE RELEASE OF GLUTAMATE AND ASPARTATE FROM RAT-BRAIN SYNAPTOSOMES IN RESPONSE TO DOMOIC ACID (AMNESIC SHELLFISH TOXIN) AND KAINIC ACID

Kainic acid is known to stimulate the release of glutamate (GLU) and aspartate (ASP) from presynaptic neurons. It has been suggested that the enhanced release of these endogenous EAA's plays a significant role in the excitotoxic effects of KA. Domoic acid (DOM), a shellfish toxin, is structurally similar to KA, and has been shown to be 3-8 times more toxic than KA. In this study, effects of KA and DOM on the release of GLU and ASP from rat brain synaptosomes were investigated. Amino acid analysis was performed by the reversed phase HPLC, following derivatization with 9-fluorenylmethyl chloroformate (FMOC). Potassium chloride (40 mM) was used as a positive control, and stimulated GLU release from rat brain synaptosomes in presence or absence of Ca2+. DOM enhanced the release of GLU, whereas KA stimulated the release of both GLU and ASP from synaptosomes in the presence of Ca2+. However, their potency to stimulate GLU and ASP release was enhanced in absence of Ca2+. These results indicate that different mechanisms may be involved in the release of GLU and ASP in response to DOM and KA, and that neurotransmitter release appeared to be highly specific for these agonists. It would appear that DOM and KA may interact with different receptors on the presynaptic nerve terminal, and/or activate different subtypes of voltage-dependent Ca2+ channels to promote influx of Ca2+ which is targeted for different pools of neurotransmitters.