| Assay Method Information | |
| | Competitive Radioligand Binding Assay |
| Description: | The affinity of candidate sigma-2 ligand compounds at sigma-1 and sigma-2 receptors was also determined by displacement of different known labeled sigma-2 or sigma-1 ligands. Filtration assays were conducted according the previously published procedure (Xu, et al., 2005). Test compounds were dissolved in N,N-Dimethylformamide (DMF), dimethyl sulfoxide (DMSO) or ethanol and then diluted in 50 mM Tris-HCl pH 7.4 buffer containing 150 mM NaCl and 100 mM EDTA. Membrane homogenates were made from guinea pig brain for sigma-1 binding assay and rat liver for sigma-2 binding assay. Membrane homogenates were diluted with 50 mM Tris-HCl buffer, pH 8.0 and incubated at 25° C. in a total volume of 150 uL in 96 well plates with the radioligand and test compounds with concentrations ranging from 0.1 nM to 10 uM. After incubation was completed, the reactions were terminated by the addition of 150 uL of ice-cold wash buffer (10 mM Tris HCl, 150 mM NaCl, pH 7.4) using a 96 channel transfer pipette (Fisher Scientific, Pittsburgh, Pa.) and the samples harvested and filtered rapidly through 96 well fiber glass filter plate (Millipore, Billerica, Mass.) that had been presoaked with 100 uL of 50 mM Tris-HCl buffer. Each filter was washed four times with 200 uL of ice-cold wash buffer (10 mM Tris-HCl, 150 mM NaCl, pH 7.4). A Wallac 1450 MicroBeta liquid scintillation counter (Perkin Elmer, Boston, Mass.) was used to quantitate the bound radioactivity. The sigma-1 receptor binding assays were conducted using guinea pig brain membrane homogenates ( 300 ug protein) and 5 nM [3H](+)-pentazocine (34.9 Ci/mmol, Perkin Elmer, Boston, Mass.), incubation time was 90 min at room temperature. Nonspecific binding was determined from samples that contained 10 μM of cold haloperidol. The sigma-2 receptor binding assays were conducted using rat liver membrane homogenates ( 300 ug protein) and 2 nM sigma-2 highly selective radioligand [3H]RHM-1 only (no other blockers) (America Radiolabeled Chemicals Inc. St. Louis, Mo.), 10 nM [3H]DTG (58.1 Ci/mmol, Perkin Elmer, Boston, Mass.) or 10 nM [3H]Haloperidol (America Radiolabeled Chemicals Inc., St. Louis, Mo.) in the presence of 1 uM (+)-pentazocine to block sigma-1 sites, incubation times were 6 minutes for [3H]RHM-1, 120 min for [3H]DTG and [3H]haloperidol at room temperature. Nonspecific binding was determined from samples that contained 10 uM of cold haloperidol. |
| Affinity data for this assay | |
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