Glutamate receptor-channels induced by brain messenger RNA in Xenopus oocytes

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The glutamate receptor-channels induced in the membrane of Xenopus laevis oocyte injected with mRNA extracted from cerebral cortex, striatum and hippocampus in the rat brain and the bovine brain were investigated electrophysiologically.(1) The oocyte resting membrane potential ranged from -50 to -60 mV. The changes in the membrane potentials were induced in 10^<-6>M concentration of glutamate and its analogues, N-methyl-D-aspartate, quisqualate and kainate. The depolarizing responses were mostly observed, but some-times the hyperpolarizing responses occurred.(2) The differences in the induction of receptor-channels were not found between mRNAs extracted from cerebral cortex, striatum and hippocampus, and between the rat brain and the bovine brain.(3) Kainate always depolarized the membranes, in a dose-dependent manner, with threshold concentration as low as 10^<-8>M. The oocyte responses to kainate were separated into the three distinct types: Type 1, the fast depolarization without repolarization for a long period; Type 2, the spike-like depolarization followed by slow depolarization in the shape of plateau; Type 3, the spike-like depolarization.(4) The antagonists to the excitatory amino acid, D- -adipate,2-amino-4-phosphonobutyric acid, glutamate diethylester and -D-glutamylglycine did not inhibit the three types of responses to kainate.(5) The responses to kainate were not sensitized.