Anti–syntaxin 2 antibody inhibits [³H]5-HT release.

(A) The permeabilized platelet exocytosis assay was performed in the presence of increasing amounts of anti–syntaxin 2 (▪), 4 (•), and 7 (▴) antibodies and rabbit IgG (⋄ (0-0.18 mg/mL). After stimulation with Ca⁺⁺ (10 μmol/L), [³H]5-HT release was measured and normalized as a percentage of control release. (B) [³H]5-HT secretion stimulated by 10 μmol/L Ca⁺⁺ was analyzed in the presence of anti–syntaxin 2 antibody (20 μg/mL), anti–syntaxin 2 antibody (20 μg/mL) preincubated with His₆–syntaxin 2 (0.24 mg/mL), His₆–syntaxin 2 alone (0.24 mg/mL), anti–syntaxin 2 antibody (0.02 mg/mL) preincubated with His₆–syntaxin 4 (0.24 mg/mL), and IgG purified from preimmune sera (20 μg/mL). The [³H]5-HT release was measured and normalized as a percentage of control release (n = 9).