| Assay Method Information | |
| | Human D1 Receptor Binding Assay |
| Description: | The affinity of the compounds described herein was determined by competition binding assays similar to those described in Ryman-Rasmussen et al., "Differential activation of adenylate cyclase and receptor internalization by novel dopamine D1 receptor agonists", Molecular Pharmacology 68(4):1039-1048 (2005). This radioligand binding assay used [3H]-SCH23390, a radiolabeled D1 ligand, to evaluate the ability of a test compound to compete with the radioligand when binding to a D1 receptor. D1 binding assays were performed using over-expressing LTK human cell lines. To determine basic assay parameters, ligand concentrations were determined from saturation binding studies where the Kd for [3H]-SCH23390 was found to be 1.3 nM. From tissue concentration curve studies, the optimal amount of tissue was determined to be 1.75 mg/mL per 96 well plate using 0.5 nM of [3H]-SCH23390. These ligand and tissue concentrations were used in time course studies to determine linearity and equilibrium conditions for binding. Binding was at equilibrium with the specified amount of tissue in 30 minutes at 37° C. From these parameters, Ki values were determined by homogenizing the specified amount of tissue for each species in 50 mM Tris (pH 7.4 at 4° C.) containing 2.0 mM MgCl2 using a Polytron and spun in a centrifuge at 40,000xg for 10 minutes. The pellet was resuspended in assay buffer [50 mM Tris (pH 7.4@ RT) containing 4 mM MgSO4 and 0.5 mM EDTA]. Incubations were initiated by the addition of 200 μL of tissue to 96-well plates containing test drugs (2.5 μL) and 0.5 nM [3H]-SCH23390 (50 μL) in a final volume of 250 μL. Non-specific binding was determined by radioligand binding in the presence of a saturating concentration of (+)-Butaclamol (10 μM), a D1 antagonist. After a 30 minute incubation period at 37° C., assay samples were rapidly filtered through Unifilter-96 GF/B PEI-coated filter plates and rinsed with 50 mM Tris buffer (pH 7.4 at 4° C.). Membrane bound [3H]-SCH23390 levels were determined by liquid scintillation counting of the filterplates in Ecolume. The IC50 value (concentration at which 50% inhibition of specific binding occurs) was calculated by linear regression of the concentration-response data in Microsoft Excel. Ki values were calculated according to the Cheng-Prusoff equation:K i = IC 50 1 + ( [ L ] / K d )where [L]=concentration of free radioligand and Kd=dissociation constant of radioligand for D1 receptor (1.3 nM for [3H]-SCH23390). |
| Affinity data for this assay | |
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