N-METHYL-D-ASPARTATE RECEPTORS - DIFFERENT SUBUNIT REQUIREMENTS FOR BINDING OF GLUTAMATE ANTAGONISTS, GLYCINE ANTAGONISTS, AND CHANNEL-BLOCKING AGENTS

Expression of the NR-1 subunit in Xenopus oocytes produces channels th at respond to glutamate and are blocked by competitive and noncompetit ive antagonists of the N-methyl-D-aspartate (NMDA) receptor. Ionic con ductances through these channels are increased by coexpression with NR -2 receptor subunits. We have characterized the pharmacological proper ties of NMDA receptors assembled from combinations of subunits express ed in transfected cells, to determine the minimum subunit requirements for binding of competitive glutamate antagonists, glycine antagonists , and channel-blocking agents, as detected by ligand-binding experimen ts. Expression of NR-1a alone produced glycine antagonist binding, whe reas the combination of NR-1a and NR-2A was needed to produce binding sites for glutamate antagonists and channel-blocking agents. These res ults suggest that functional NMDA receptors assemble from these subuni ts. However, differences in the pharmacological effects of NMDA and po lyamines show that not all characteristics of native NMDA receptors ar e reproduced by this combination of subunits.