Partial agonist activity at D2L receptor in human HTLA cells assessed as beta arrestin recruitment at 6 uM after 18 hrs by luminescence assay relative to Quinpirole
Partial agonist activity at human D2L receptor expressed in HEK293T cells coexpressing Gi subunit assessed as inhibition of isoproterenol-stimulated cAMP production by luminescence assay relative to quinpirole
Partial agonist activity at human D2L receptor expressed in HEK293T cells coexpressing Gi subunit assessed as inhibition of isoproterenol-stimulated cAMP production by luminescence assay
Radioligand Binding Assay: Membranes prepared as above were resuspended to 1 ug protein/ul (measured by Bradford assay using BSA as standard), and 50 ul were added to each well of a polypropylene 96-well plate containing (per well): 50 ul of buffer (20 mM HEPES, 10 mM MgCl2, 1 mM EDTA, 1 mM EGTA, 100 mM N-methyl-D-gluconate, pH 7.4), 50 ul of 1.5 nM [3H]N-methylspiperone (final concentration 0.3 nM) and reference or D2 test ligand at various concentrations ranging from 50 uM to 50 uM (final concentrations ranging from 10 uM to 10 uM, triplicate determinations for each concentration of D2 test ligand). After a 1.5-hr incubation in the dark at room temperature, the reactions were harvested onto 0.3% PEI-soaked Filtermax GF/A filters (Wallac) and washed three times with ice-cold 50 mM Tris, pH 7.4 using a Perkin-Elmer Filtermate 96-well harvester. The filters were subsequently dried, placed on a hot plate (100° C.), and Melitilex-A (Wallac) scintillant was applied.
Beta-Arrestin Recruitment (Tango) Assay: Recruitment of β-arrestin to agonist-stimulated D2 receptors was performed using a previously described Tango-type assay (Barnea et al., Proc. Natl. Acad. Sci. USA 105:64 (2008)). Briefly, HTLA cells stably expressing β-arrestin-TEV protease and a tetracycline transactivator-driven luciferase were plated in 15-cm dishes in DMEM containing 10% fetal bovine serum and transfected (via calcium phosphate) with 20 μg of a D2V2-TCS-tTA construct (Barnea et al., Proc. Natl. Acad. Sci. USA 105:64 (2008)). The next day, cells were plated in white, clear-bottom, 384-well plates (Greiner, 10,000 cells/well, 50 μl/well) in DMEM containing 1% dialyzed fetal bovine serum. The following day, the cells were challenged with 10 μl/well of reference agonist (6 μM) or D2 test ligand (6 μM)±reference agonist prepared in HBS, 20 mM HEPES, pH 7.4, 18% DMSO (final ligand concentrations were 1 μM, final DMSO concentration was 3%).