The fasting blood samples were obtained from the cubital veins of healthy volunteer with informed consent. The sample were collected in the vacuum tube containing sodium citrate as anticoagulant (9∶1). After collection, the sample was kept at room temperature for an hour to obtain a layer of plasma containing platelets. In the next step, the sample was labeled with fluorescent calcium probe Fluo-4-AM (Thermo Fisher Scientific, USA). The stock solution (1 mM) of Fluo-4-AM was diluted 62.5 times in phosphate buffered saline (PBS) and mixed 1:1 with blood plasma. After incubation for 30 minutes in the dark, the sample was 10 times diluted in PBS with or without compound 2a or 2b, placed in a well of 96-well plate and allowed to rest for another 30 minutes before experiments. Calcium signaling in individual platelets was recorded using CarlZeiss AxioVert.A1 fluorescence microscope with 20x objective.