The human NMDA receptor GluN2A variant influences channel blocker potency.

-methyl-D-aspartate (NMDA) receptors are glutamate receptors with key roles in synaptic plasticity, due in part to their Mg mediated voltage-dependence. A large number of genetic variants affecting NMDA receptor subunits have been found in people with a range of neurodevelopmental disorders, including GluN2A () in two unrelated individuals with severe epileptic encephalopathy. This missense variant substitutes a lysine in place of an asparagine known to be important for blockade by Mg and other small molecule channel blockers. We therefore measured the impact of GluN2A on a range of NMDA receptor channel blockers using two-electrode voltage clamp recordings made in oocytes. We found that GluN2A resulted in block by Mg 1 mmol/L being greatly reduced (89% vs 8%), block by memantine 10 μmol/L (76% vs 27%) and amantadine 100 μmol/L (45% vs 17%) being substantially reduced, block by ketamine 10 μmol/L being modestly reduced (79% vs 73%) and block by dextromethorphan 10 μmol/L being enhanced (45% vs 55%). Coapplying Mg with memantine or amantadine did not reduce the GluN2A block seen with either small molecule. In addition, we measured single-channel conductance of GluN2A-containing NMDA receptors in outside-out patches pulled from oocytes, finding a 4-fold reduction in conductance (58 vs 15 pS). In conclusion, the GluN2A variant is associated with substantial changes to important physiological and pharmacological properties of the NMDA receptor. Our findings are consistent with GluN2A having a disease-causing role, and inform potential therapeutic strategies.