CHEMBL5737675

Biological Assay (standard): NMDA receptors are ion channels that are highly permeable to Ca2+ ions, rendering it possible to monitor NMDA receptor function using cell-based calcium flux assay. In this assay, co-agonists glutamate and glycine are added to cells heterologously expressing human GluN1/GluN2B NMDA receptors to initiate cellular Ca2+ influx. The time course of the changes in intracellular calcium is measured using a fluorescent dye and a FLIPR (Fluorometric Imaging Plate Reader) device.Twenty four hours before measurements, the expression of the NMDA receptors in the stable cell line is induced with Tet-On inducible system in the presence of a non-selective NMDA receptor blocker. On the day of the experiment, cell culture media is carefully washed and the cells are loaded with Calcium 5 Dye Kit (Molecular Devices) in dye loading buffer containing 137 mM NaCl, 4 mM KCl, 2 mM CaCl2), 0.5 mM MgCl2, 10 mM HEPES and 5 mM D-glucose; pH 7.4. After 1 h incubation at the room temperature, the dye is washed away with the assay buffer (137 mM NaCl, 4 mM KCl, 2 mM CaCl2), 0.01 mM EDTA, 10 mM HEPES and 5 mM D-glucose; pH 7.4) In the FLIPR TETRA reader, various concentrations of the test compounds are added to the cells for 5 min while fluorescence is monitored to detect potential agonist activity. Next, co-agonists, glutamate and glycine are added for another 5 minutes. The concentration of glutamate corresponding to ~EC40 used to maximize the assay's signal window and ability to detect NMDA receptor antagonists and negative allosteric modulators. A saturating concentration (10 μM) of glycine is also present in the assay. A non-selective NMDA receptor antagonist, (+)MK-801 is used as a positive control for antagonist activity. The fluorescent signal in the presence of test compounds is quantified and normalized to the signal defined by the appropriate control wells.