Exogenously added α-synuclein has no effect on ionomycin- or thrombin-induced [³H]5-HT release and hexosaminidase release from platelets.

(A) Platelet-rich plasma was incubated with 0.037 MBq (1 μCi) per milliliter [³H]5-HT for 60 minutes at room temperature to enable sufficient uptake. Platelets were resuspended in HEPES-buffered saline containing 0.1% BSA and were stimulated with either 1 μM ionomycin or 1 U/mL thrombin in the presence or absence of 2 μM imipramine, as described in “Materials and methods.” After the platelet stimulation assay, 50 μL supernatant was added to a 5 mL cocktail solution, and the radioactivity was measured using a liquid scintillation counter. (B) α-Synuclein has no effect on ionomycin-induced [³H]5-HT release from the dense granules. (C) α-Synuclein has no effect on thrombin-induced [³H]5-HT release from the dense granules in the presence of 2 μM imipramine. (D) Ionomycin-induced lysosomal granule release was measured by a quantitative β-hexosaminidase assay, as described in “Materials and methods.” (E) Ionomycin-induced hexosaminidase release from lysosomal granules is not affected by exogenously added α-synuclein, GST-α-synuclein, or α-synuclein112.