Effect of ABT-737 on platelet calcium signaling. (A) Washed platelets loaded with Fura-2 (1 × 10⁸/mL) were treated with ABT-737 (10μM; gray trace) or DMSO (black trace) in the presence of extracellular CaCl₂ (1mM), followed by stimulation with thrombin (0.1 U/mL). The initial section of the traces are expanded and separated below to show the small ABT-737–induced signal. Fluorescence was calibrated in terms of cytosolic calcium concentration to estimate the magnitude of the response.⁶  (B) Platelets in modified Tyrode buffer were treated with ABT-737 (10μM) or DMSO or for the indicated time then treated with EGTA (1.2mM) followed by ionomycin (Iono; 1μM) to artificially deplete calcium stores. Traces are representative of at least 3 independent experiments. All experiments were performed at 37°C under stirring conditions.