Effects of activation inhibitors on Ca²⁺ responses of single platelets bound to collagen. Fura-2–loaded platelets were treated with the indicated drugs and allowed to adhere to collagen in the presence of 2 mmol/L CaCl₂ and FITC-labeled annexin V during 15 minutes. Changes in fura-2 fluorescence ratio and FITC-annexin V fluorescence intensity were recorded from one microscopic field as described in Materials and Methods. Shown are typical Ca²⁺ response patterns of single platelets, representative of 36 to 76 cells, for the following conditions: control (A); CaCl₂ replaced by 1 mmol/L EGTA (B); platelets pretreated with 100 μmol/L aspirin (C) or dimethyl BAPTA (E) while loading with fura-2; platelets incubated with 5 μmol/L prostaglandin E₁ for 5 minutes (D), with 100 μmol/L genistein for 30 minutes (F ), with 20 μmol/L U73343 for 5 minutes (G), or with 10 μmol/L wortmannin for 5 minutes (H).