Platelet aggregation and secretion responses. Aggregation studies were performed using a whole-blood lumiionized calcium aggregation system (Chrono-Log). Four hundred microliters of washed platelets in Tyrode-HEPES buffer at 2.5 × 108 platelets/mL were added to siliconized glass cuvettes at 37° C with constant stirring at 1000 rpm. CaCl2 was added to a final concentration of 1 mM, and fibrinogen (Sigma Chemical, St Louis, MO) was added to 300 μg/mL. Platelets from the patient or a healthy control subject were stimulated with thrombin receptor activating peptide (TRAP), arachidonic acid (AA), ristocetin (Risto), ADP, collagen, or CRP. Aggregation was monitored by measuring an increase in light transmission. Secretion is shown in green for arachidonic acid and collagen and in black for TRAP and ADP. Note the specific failure of collagen or the GPVI-specific agonist CRP to induce platelet aggregation or secretion (arrows).
