Potencies and unblocking kinetic properties of antagonists at recombinant human NMDA receptors in a Xenopus oocytes model.

N-methyl-D-aspartate (NMDA) receptor channels are implicated in a wide range of physiological and pathophysiological processes, and a large number of pharmacological agents have been introduced that target the receptor via diverse mechanisms of action. Amongst others, subunit selectivity (in particular for the NR2B receptor subunit) and rapid unblocking kinetics have been put forward as favourable pharmacological properties of NMDA receptor-targeting drugs. Here, we describe a pharmacological characterization of human recombinant NMDA receptors expressed in Xenopus oocytes in an electrophysiological set-up. Using this approach, we compare inhibitor potencies of several known NMDA receptor ligands as well as unblocking kinetic properties of selected compounds. All compounds tested had similar potencies at receptors containing NR2A or NR2B receptors with the exception of traxoprodil, which was selective for NR2B. The rank order of potency was (+)MK-801 > phencyclidine (PCP) ≈ traxoprodil > memantine ≈ ketamine > duloxetine. In line with its proposed rapid dissociation properties, the relatively well-tolerated drug memantine exhibits markedly faster unblocking than ketamine and PCP, similar to the low-affinity compound, duloxetine. Electrophysiological recording in Xenopus oocytes thus allows a relatively convenient comparison of key pharmacological parameters at recombinant human NMDA receptors.