Assay Method Information

Assay Name:  [35S]GTPγS Binding Assay
Description:  [35S]GTPγS binding was performed as previously described [Brents et al., PLoS One, 6:e21917]. Briefly, 25 μg of mouse brain homogenates were incubated for 30 minutes at 30° C. with 0.1 nM [35S]GTPγS, 10 μM GDP, and either cannabinoid+/−antagonist, 10 μM unlabeled GTPγS (non-specific binding) or vehicle (total binding), in triplicate, in a volume of 1 mL of buffer containing 20 mM HEPES, 10 mM MgCl2, 100 mM NaCl, 20 units/L adenosine deaminase, 0.05% BSA and the appropriate DMSO (0.1%) and/or ethanol (<0.2%) vehicle. Assay buffer containing 100 mM KCl, instead of 100 mM NaCl, was used to increase basal G-protein activity in experiments examining inverse agonism. Reactions were terminated by quick vacuum filtration through Whatman GF/B glass fiber filters, followed by five washes with ice-cold buffer (20 mM HEPES, 0.05% BSA). Filters were immediately placed into 7 mL scintillation vials to which 4 mL of ScintiVerse™ BD Cocktail scintillation fluid was added. Bound radioactivity was determined after overnight incubation at room temperature and shaking by liquid scintillation spectrophotometry with an efficiency of 93% (Tri Carb 2100 TR Liquid Scintillation Analyzer, Packard Instrument Company, Meriden, Conn.).
Affinity data for this assay
 

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