A specific quisqualate agonist inhibits kainate responses induced in Xenopus oocytes injected with rat brain RNA.

Electrophysiological recording was used to study non-N-methyl-D-aspartate (NMDA) excitatory amino acid (EAA) receptors after injection of rat brain ribonucleic acid (RNA) in Xenopus laevis oocytes. Quisqualate (QA) induced two types of responses, a smooth one and an oscillatory one. These responses are probably mediated by the ionotropic (QAi, a cationic channel) and the metabotropic (QAp, a newly discovered receptor coupled to phospholipase C) QA receptors respectively. alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) only induced a smooth inward current suggesting that it acts only on QAi. Kainate (KA) also induced a smooth inward current, the maximal KA response being 10-fold higher than the maximal AMPA. AMPA inhibited the KA response in a dose-dependent and competitive manner. Amongst various complex hypotheses the simplest to explain these results would be that KA and AMPA both activate the same receptor-channel complex, AMPA inducing a smaller response than KA.