Effect of AAPP on [Ca2+]i in the early phase of collagen stimulation. Fura-2 AM-loaded platelets were incubated with 1 mM CaCl2 for 5 minutes. Collagen (0.5 μg/mL) was added after a 60-second incubation with rAAPP (30, 100 or 300 nM), and the fura-2 fluorescence was determined. Tracings are representative results of a typical experiment.