Figure 7.

Thrombin-induced secretion is defective in endobrevin/VAMP-8^−/− platelets. Platelets from wild-type (WT, •) and VAMP-8^−/− (V8^−/−, ○) mice were prepared as described. After adding 0.7 mM CaCl₂, aliquots (50 μl; 2.5 × 10⁸/ml) were incubated with the indicated concentration of thrombin at RT for 1 min (A) or 0.05 U/ml thrombin for the indicated time points (B). Reactions were stopped with hirudin. Release of [³H]5-HT from dense core granules (DC), PF4 from alpha granules (Alpha), and β-hexosaminidase from lysosomes (Lysosome) were measured, and percent secretion was calculated. Each data point represents the mean values of triplicate samples, and the SD is indicated.