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Assay Method Information

Assay Name:  Intracellular Calcium Measurement to Assess Antagonist Activity at Human P2X3 and Human P2X2/3 Receptors
Description:  A fluorescent imaging plate reader (FLEX/FLIPR station; Molecular Devices) was used to monitor intracellular calcium levels using the calcium-chelating dye Fluo-4 (Molecular Probes). The excitation and emission wavelengths used to monitor fluorescence were 470-495 nm and 515-575 nm, respectively. Cells expressing purinergic receptors P2X3 (human) or P2X2/3 (human) were plated at a density of 15,000 cells/well in collagen-coated 384-well plates approximately 20 hours before beginning the assay. On the day of the assay, 20 μl of loading buffer (Hank's balanced salt solution, 20 mM HEPES, 0.5 mM CaCl2, 0.5 mM MgCl2, 0.1% BSA, 5 mM probenecid, 10 mM D-glucose monohydrate, 2 μM Fluo-4, and 5 units/mL, hexokinase, pH=7.4) was added and cells dye-loaded for 90 min at 37 C. The dye supernatant was removed and replaced with 45 μl probenecid buffer (Hank's balanced salt solution, 20 mM HEPES, 0.5 mM CaCl2, 0.5 mM MgCl2, 0.1% BSA, 5 mM probenecid, 10 mM D-glucose monohydrate, pH=7.4). The test compound was added in a volume of 5 μl and allowed to incubate for 30 min at 37 C. The final assay DMSO concentration is 1%. The agonist, α,β-Me-ATP, was added in a volume of 20 μl at a concentration representing the EC80 value. The fluorescence was measured for an interval of 90 sec at 2 sec intervals and analyzed based on the increase in peak relative fluorescence units (RFU) compared to the basal fluorescence. Peak fluorescence was used to determine the response to agonist obtained at each concentration of test compound by the following equation: % Response=100*(RFU(test compound)−RFU(control))/(RFU(DMSO)−RFU(control))The Examples were tested in triplicates per plate and mean values were plotted in Excel XLFit to determine IC50 values at the human P2X3 and human P2X2/3 receptors, percentage of maximal inhibition and the Hill coefficients.
Affinity data for this assay
 

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Last update November 1, 2007
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