Inhibition of NMDA receptors through a membrane-to-channel path

Abstract

N-methyl-d-aspartate receptors (NMDARs) are transmembrane proteins that are activated by the neurotransmitter glutamate and are found at most excitatory vertebrate synapses. NMDAR channel blockers, an antagonist class of broad pharmacological and clinical significance, inhibit by occluding the NMDAR ion channel. A vast literature demonstrates that NMDAR channel blockers, including MK-801, phencyclidine, ketamine, and the Alzheimer’s disease drug memantine, can bind and unbind only when the NMDAR channel is open. Here we use electrophysiological recordings from transfected tsA201 cells and cultured neurons, NMDAR structural modeling, and custom-synthesized compounds to show that NMDAR channel blockers can enter the channel through two routes: the well-known hydrophilic path from extracellular solution to channel through the open channel gate, and also a hydrophobic path from plasma membrane to channel through a gated fenestration (“membrane-to-channel inhibition” (MCI)). Our demonstration that ligand-gated channels are subject to MCI, as are voltage-gated channels, highlights the broad expression of this inhibitory mechanism.

Potent and reversible open-channel blocker of NMDA receptor derived from dizocilpine with enhanced membrane-to-channel inhibition

“…4G,H) and 100 µM memantine (Glasgow et al, 2018; Kolcheva et al, 2021). Recent data have shown that the GluN2A-M630 amino acid residue lines the fenestration of memantine via MCI (Wilcox et al, 2022). Therefore, we next assessed whether GluN1/GluN2A receptors with the mutated GluN2A-M630 residue exhibit altered MCI induced by K2060 (Fig.…”

“…In addition, we observed a decrease in τ slow and A slow in the presence of Mg 2+ , which may also be attributable to the reduction of MCI induced by K2060 in the presence of Mg 2+ . In the case of memantine, MCI was explained by the presence of a fraction of the uncharged form that interacts with the membrane and then fenestrates into the ion channel of the GluN1/GluN2 receptor (Wilcox et al, 2022). The stronger MCI of K2060 may be explained by differential lipophilicity (memantine clogP = 2.07; MK-801 clogP = 3.31; K2060 clogP = 4.59; MarvinSketch software v. 23.8; estimated values), although both memantine and K2060 are likely to wash off the membrane in the order of seconds (Kotermanski and Johnson, 2009).…”

“…These different pharmacological effects in vivo likely result from their differences in the molecular mechanism of action at the NMDARs. Although both memantine and ketamine bind into ion channel pore relatively weakly (”low-affinity” open-channel blockers) (Song et al, 2018; Zhang et al, 2021), memantine—but not ketaminedisplays a second type of low-affinity inhibition (Blanpied et al, 1997; Sobolevsky et al, 1998; Kotermanski and Johnson, 2009; Glasgow et al, 2018), by accessing the binding site via a hydrophobic route from the plasma membrane to ion channel through a gated fenestration (named “membrane-to-channel inhibition” (MCI)) (Wilcox et al, 2022). On the contrary, the psychomimetic effect of MK-801 can be ascribed to its “high-affinity “and almost “irreversible” binding within the ion channel pore of GluN1/GluN2 receptors (Song et al, 2018).…”

Sub-clinical glutamate receptor antagonist combinations prevent progressive demyelination

“…The memantine/perampanel CLD-GA paradigm that is effective against CPZ-induced white matter injury was based on doses an order of magnitude below the clinical treatment range for these drugs and is an attractive alternative to full-dose co-administration such as that tested in stage II clinical trials for glioblastoma (eg., 34 ). Membrane-to-channel inhibition has recently been described for lipophilic antagonists of NMDA and AMPA receptors, which can diffuse from the cell membrane into the receptor protein via gated fenestration 35,36 . To take advantage of this phenomena and further extend the clinical potential of the CLD approach, we tested a combination of two experimental antagonists that are structural analogues of myelin-targeting fluorescent dyes.…”

Structure of an insect gustatory receptor

“…Fenestrations in the pore walls are observed in all available structures and density consistent with a lipid is present in both agonist-free and fructose-bound BmGr9 structures, suggesting that the lipids form part of a stable pore structure. Fenestrations opening the ion path to the membrane environment have been observed in several other ion channel families, including ionotropic glutamate receptors, cys-loop receptors, voltage-gated potassium channels and sodium channels, and mechanosensitive two-pore domain potassium (K2P) channels [35][36][37][38][39] . In some channels, such fenestrations are transient, while in others they are observed in both closed and open channel states.…”