| Assay Method Information | |
| | Binding Assay |
| Description: | The affinities of the target compounds were determined using radioligand binding experiments. All radioligand binding experiments were performed according to previously described methods (Luedtke R. R. et al. Synapse 2000, 38, 438-449; Chu, W. et al. Bioorg. Med. Chem. 2005, 13, 77-87; Taylor, M. et al. Synapse 2010, 64, 251-266). Stably transfected HEK cells expressing the human D2-long and the D3 dopamine receptor were developed using the pIRESneo2 bicistronic expression vector (Clontech, Palo Alto, Calif.). Levels of expression of human D2 and D3 dopamine receptors in HEK cells were 57,941±14,686 fmol/mg protein and 4202±1516 fmol/mg protein, respectively. Competition curves were performed using 125I-IABN. Membrane homogenates (50 μL) were suspended in 50 mM Tris-HCl/150 mM NaCl/10 mM EDTA buffer, pH 7.5 and incubated with 50 μL of 125I-IABN at 37° C. for 60 min. Nonspecific binding was defined using 4 μM (+)-butaclamol. The radioligand concentration used was approximately equal to the Kd value, and the concentration of the competitive inhibitor ranged over five orders of magnitude. Binding was terminated by the addition of cold wash buffer (10 mM Tris-HCl/150 mM NaCl, pH 7.4) and filtration over a glass-fiber filter (Schleicher and Schuell No. 32). Filters were washed with 10 mL of cold buffer, and the radioactivity was quantitated. A Packard Cobra gamma counter was used for 125I-labeled radioligands (efficiency=75%). The protein concentration was determined using a BCA reagent (Pierce) with bovine serum albumin as the protein standard. Data from competitive inhibition experiments was modeled using nonlinear regression analysis to determine the concentration of inhibitor that inhibits 50% of the specific binding of the radioligand (IC50 value). Competition curves were modeled for a single site. Data from competition dose-response curves were analyzed using Tablecurve program (Jandel). IC50 values were converted to equilibrium dissociation constants (Ki values) using the Cheng and Prusoff correction. |
| Affinity data for this assay | |
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