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Assay Method Information

Assay Name:  Radioligand Binding Assay
Description:  Plasma membranes prepared from HEK 293 EBNA cells transfected with human CB1 or CB2 cannabinoid receptors (3.7 or 3.3 pmol/mg protein, receptor concentration; PerkinElmer) were used for the radioligand binding studies. The composition of incubation buffer for CB1 assay was 50 mM Tris base, 2.5 mM EDTA, 5 mM MgCl2 and 0.5 mg/ml fatty acid free BSA and for CB2 assay was 50 mM Tris base, 2.5 mM EGTA, 5 mM MgCl2 and 1 mg/ml fatty acid free BSA; pH was adjusted to 7.4 by adding 1N HCl. Plasma membranes were diluted with incubation buffer to provide a final protein concentration of 2.4 μg (CB1) or 8 μg (CB2) per well in non-binding surface polystyrene 96-well assay plates (Corning). Compound solutions were prepared in silanized glass tubes and dispensed using pipette tips with SUPERSLIK┐ surface. Competition studies were performed using a final concentration of 0.72 nM [3H]-CP 55,940 (100-180 Ci/mmol, specific activity; PerkinElmer) against test compounds. Non-specific binding was determined using 10 uM of unlabeled CP 55,940. Incubations were performed in 96-well assay plates at a final volume of 200 ul for 90 min (CB1) or 60 min (CB2) at room temperature. Binding reactions were terminated by the addition of ice-cold incubation buffer and rapid filtration through a glass fiber filter using a cell harvester (Inotech). This was followed by 8 additional washes. The glass fiber filter (0.26 mm thickness, 1-1.5 um retention; Inotech) was presoaked in cold incubation buffer containing 0.05% polyethylenimine. The filters were oven-dried at 50░ C. for 60 min and counting performed using a Beckman Coulter LS 6500 Multi-Purpose Scintillation Counter (Beckman-Coulter). Binding was determined in duplicate for at least 4 separate experiments.
Affinity data for this assay
 

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Last update November 1, 2007
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