Subtype-Dependence of NMDA Receptor Channel Open Probability

Abstract

NMDA receptor-mediated calcium transients play a critical role in synaptogenesis, synaptic plasticity, and excitotoxicity. NMDA receptors are heteromeric complexes of NR1A combined with NR2A, NR2B, NR2C, and/or NR2D subunits. The NR2 subunits determine a variety of electrophysiological and pharmacological properties of the NMDA receptor complex. In this report, we provide evidence for the first time that there is also a significant difference in peak channel open probability (P(o)) between NMDA receptors composed of NR1A/NR2A and those of NR1A/NR2B subunits. First, whole-cell patch-clamp recordings from human embryonic kidney (HEK) 293 cells expressing NMDA receptors revealed that NR1A/NR2A-mediated peak current densities are approximately four times larger than those of NR1A/NR2B. We show that this fourfold difference is unlikely caused by differences in receptor surface expression, since these levels were similar for the two subtypes by Western blot analysis. To determine whether P(o) contributed to the difference in peak current densities, we used two different open channel antagonists, MK-801 and 9-aminoacridine, in a variety of experimental paradigms. Our results indicate that peak P(o) is significantly higher (twofold to fivefold) for NR1A/NR2A than NR1A/NR2B, with estimated values of approximately 0.35 and 0.07, respectively. These results suggest that a change in the relative expression levels of NR2A and NR2B can regulate peak amplitude of NMDA receptor-mediated excitatory postsynaptic potentials and therefore may play a role in mechanisms underlying synaptic plasticity.

Genetically encoding a light switch in an ionotropic glutamate receptor reveals subunit-specific interfaces

“…1A). Using conventional mutagenesis to introduce point mutations at this site, we found that, depending on the side chain property, receptor gating can be bidirectionally manipulated, as assessed by the inhibition kinetics of MK-801, a selective NMDAR open-channel blocker classically used to index receptor channel P o (15,18,19) (SI Appendix, Fig. S1 A and B).…”

Metabotropic Glutamate Receptor Subtype 5 Antagonists MPEP and MTEP

“…Through the mGluRs, glutamate can modulate excitatory (AMPA and NMDA receptors) and inhibitory (GABA) signaling pathways, in addition to various ion channels, including many specific for potassium and calcium (9,21,46,52,86,100,101,175,179,186,213). Because these systems are inherently involved in the function and pathophysiology of CNS, drugs that modulate mGluRs can have multiple modulatory/therapeutic effects throughout the CNS.…”

Subtype-dependent N-Methyl-d-aspartate Receptor Amino-terminal Domain Conformations and Modulation by Spermine

“…The ATDs of glutamate receptors are known to be involved in receptor assembly and in controlling the open probability of the receptor (1)(2)(3). Specifically, receptors composed of GluN1-GluN2A subunits exhibit a higher channel open probability than those composed of GluN1-GluN2B subunits (4,5). This inherent difference in the open probabilities arises, to a large extent, from the ATDs, as switching the ATD of GluN2A with that of GluN2B results in a swap in the channel open probabilities, albeit not completely (2).…”