Evaluation of SNAP-23, syntaxin-2, and VAMP-3 on the extracellular surface of activated platelets exposed to trypsin. One set of platelets (BEFORE TRYPSIN) was exposed to either buffer alone, SFLLRN, or PMA and subsequently stained with (A) anti–SNAP-23 IgG, (B) anti–syntaxin-2 IgG, or (C) anti-VAMP-3 IgG. A second set of platelets (AFTER TRYPSIN) exposed to buffer alone, SFLLRN, or PMA was incubated with 5 μg/mL trypsin. Following a 60-minute incubation, trypsin was neutralized using an inhibitor cocktail and platelets were stained with (A) anti–SNAP-23 IgG, (B) anti–syntaxin-2 IgG, or (C) anti-VAMP-3 IgG. Values are reported as percent of control compared with signal detected in unstimulated samples exposed to nonimmune antibodies. Error bars represent the standard deviation of 3 to 6 independent experiments.