| Assay Method Information | |
| | Inhibition Assay |
| Description: | To determine their in vitro action on human PDE 5, the test substances are dissolved in 100% DMSO and serially diluted. Typically, dilution series (1:3) from 200 uM to 0.091 uM are prepared (resulting final concentrations in the test: 4 uM to 0.0018 uM). In each case 2 ul of the diluted substance solutions are placed into the wells of microtitre plates (Isoplate-96/200W; Perkin Elmer). Subsequently, 50 ul of a dilution of the above-described PDE 5 preparation are added. The dilution of the PDE 5 preparation is chosen such that during the later incubation less than 70% of the substrate are converted (typical dilution: 1:100; dilution buffer: 50 mM Tris/hydrochloric acid pH 7.5, 8.3 mM magnesium chloride, 1.7 mM EDTA, 0.2% BSA). The substrate, [8-3H] cyclic guanosine-3',5'-monophosphate (1 uCi/ul; Perkin Elmer) is diluted 1:2000 with assay buffer (50 mM tris/hydrochloric acid pH 7.5, 8.3 mM magnesium chloride, 1.7 mM EDTA) to a concentration of 0.0005 uCi/ul. By addition of 50 ul (0.025 uCi) of the diluted substrate, the enzyme reaction is finally started. The test mixtures are incubated at room temperature for 60 min and the reaction is stopped by adding 25 ul of a suspension of 18 mg/ml yttrium scintillation proximity beads in water (phosphodiesterase beads for SPA assays, RPNQ 0150, Perkin Elmer). The microtitre plates are sealed with a film and left to stand at room temperature for 60 min. Subsequently, the plates are analysed for 30 s per well in a Microbeta scintillation counter (Perkin Elmer). IC50 values are determined using the graphic plot of the substance concentration against percentage PDE 5 inhibition. |
| Affinity data for this assay | |
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