Effect of GIRK channel blockers on thrombin receptor activating peptide (TRAP)–induced aggregation and dense granule secretion. Aspirin-treated, washed platelets were activated with 10 μM SFLLRN and the corresponding aggregation or the amount of ATP secreted from dense granules (luciferin-luciferase assay) was measured as mentioned in “Materials and methods.” Arrow indicates addition of the agonist. Data are representative of 3 independent experiments done using platelets from 3 donors.