PN-1 is stored in platelet α-granules. (A) Washed platelets from control donors or patients with a GPS were activated by 50μM PAR1-AP for 30 minutes at 37°C and centrifuged to separate platelet pellets from supernatants. Platelet pellets (cell extracts) and supernatants (secretion products) were analyzed by Western blot for PN-1, GAPDH, and GPIb. (B) Washed platelets from control donor or GPS patients were analyzed by flow cytometry with an FITC-coupled anti–PN-1 IgG. Data are representative of 3 separate experiments from different donors.