A new potent excitant, quisqualic acid: effects on crayfish neuromuscular junction.

Abstract The effect of quisqualic acid, an amino acid obtained from the seed of Quisqualis indica L., on the neuromuscular junction of the crayfish was investigated. Potential changes were recorded intracellularly from muscle fibres with a microelectrode. Bath application of quisqualic acid produced a large depolarization of the muscle fibre. The depolarizing action of quisqualic acid was 500–1000 times more potent than that of l -glutamic acid on a molar basis. The iontophoretic application of quisqualic acid to the l -glutamate sensitive spot produced a large depolarization. The distribution of the quisqualate sensitive spot coincided with that of the l -glutamate sensitive spot. When the synaptic transmission was blocked by replacing the bath solution with Ca2+-free solution, the amplitude of the depolarization produced by quisqualic acid was as large as in normal calcium solution. When desensitization was induced by steady application of l -glutamate and, as a result, the response to glutamate declined, the addition of quisqualic acid produced no potential change. Conversely, quisqualic acid induced desensitization of the receptor to l -glutamic acid.