PREVENTION OF DESENSITIZATION OF THE GLUTAMATE RECEPTOR ON THE CRAYFISH OPENER MUSCLE BY CONCANAVALINA

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The effect of concanavalin A (Con A) on desensitization of the glutamate receptor was investigated in the crayfish opener muscle. The depolarization of the crayfish muscle fibre caused by bath applied L-glutamate was greatly augmented after exposure of the muscle fibre to Con A (10^-6 M) for more than 30 minutes, whereas the depolarization produced by bathapplied quisqualate was not increased by Con A. This augmentation of the glutamate-induced depolarization was more remarkable in relatively high concentrations of L-glutamate than in lower concentrations. Although both glutamate and quisqualate potentials caused by brief iontophoretic application were not so much affected by previous application of Con A, the decline of the depolarization produced by steady iontophoretic application of L-glutamate and quisqualate was completely prevented after exposure to Con A (10^-6 M). The decrease in amplitude of both glutamate and quisqualate potentials induced by train pulses was completely blocked by Con A. The slight depolarization produced by kainic acid was not augmented by previous application of Con A. Con A has no influence upon the refractory form of the receptor but prevented the conversion of the effective form into the refractory one. GABA receptors were not affected by Con A. These results suggest that Con A does not potentiate the depolarizing action of glutamate agonists on the crayfish muscle fibre but prevents the development of desensitization of the glutamate receptor.