Fibrinogen inhibits store-mediated Ca⁺⁺entry.

(A) Fura-2–loaded human platelets suspended in HBS containing 1 mM Ca⁺⁺ were stimulated with TG (1 μM) in the absence (Control) or presence of either fibrinogen (1 mg/mL) (FG) or fibrinogen after the addition of 100 μM RGDS (FG + RGDS). (B) Human platelets were stimulated in a Ca⁺⁺-free medium (100 μM EGTA) with ΤG (200 nM) in the absence (Control) or presence of fibrinogen 1 mg/mL (FG) or fibrinogen after the addition of (100 μM) RGDS (FG + RGDS). Three minutes later, CaCl₂ (final concentration, 300 μM) was added to the medium to initiate Ca⁺⁺ entry. Traces shown are representative of 5 to 6 independent experiments.