Excitatory Amino Acid Receptors in the Xenopus Oocyte Expression System

The excitatory amino acid (EAA) receptors are neurotransmitter receptors responsive to glutamate, aspartate, and perhaps also to homocysteate or related compounds (Fonnum, 1984; Do et al., 1986). Although the nomenclature is still somewhat unsettled, electrophysiologists have identified at least two EAA receptors, namely the well-known N-methyl-D-aspartate (NMDA) receptor and a less well characterized “non-NMDA” receptor that can be powerfully activated by kainic acid and (RS)-α-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA). A third receptor, stimulated by glutamate, quisqualate and ibotenate, is linked via a G-protein to the activation of phospholipase C and consequent generation of the second messenger, inositol tnsphosphate (Sugiyama et al., 1987). Due to their speed of activation (within millisec of applying agonist, e.g., Benveniste et al., 1990), the NMDA and non-NMDA receptors are thought to be receptor-channel complexes similar in architecture to the nicotinic acetylcholine receptor; i.e., all ligand binding sites and ion permeation pathways are thought to reside within the same macromolecular complex. The discussion that follows focuses on these two receptor-channel complexes.