Effect of GIRK channel blockers on ADP-induced platelet aggregation, TXA₂ generation, and dense granule secretion in non–aspirin-treated human platelets. Washed non–aspirin-treated human platelets (A-B,D-G) or aspirin-treated human platelets (C) were stimulated with ADP (10 μM) (A-F) or 2MeSADP (100 nM) (G) for 3.5 minutes under stirring conditions at 37°C in the presence and absence of different concentrations of SCH23390, or U50488H. Fibrinogen (1 mg/mL) was added to all the samples prior to the addition of the agonist. In panels A, B, and C, platelet aggregation was measured by measuring light transmittance. In panels D and F, and G, TXB₂ levels were analyzed as described in “Materials and methods.” In panel E, ATP secretion was measured as described in “Materials and methods.” In panels D and E, different concentrations of SCH23390 or U50488H were used as indicated. In panels F and G, 10-μM concentrations of SCH23390, U50488H, or SKF38393 were used. The data are represented as percent maximal TXB₂ generated by ADP or 2MeSADP in the absence of antagonists. Each bar is the average of 3 experiments ± SEM from 3 different donors.