Dual Roles of Quercetin in Platelets: Phosphoinositide-3-Kinase and MAP Kinases Inhibition, and cAMP-Dependent Vasodilator-Stimulated Phosphoprotein Stimulation

Figure 2

Quercetin influences collagen-activated granule secretions. Platelets were preincubated with quercetin and stirred in an aggregometer for 2 min before collagen or thrombin stimulation for 5 min and the reaction was terminated followed by granule secretion assay. ((a) and (b)) Effect of quercetin on collagen-induced P-selectin expression. (a) Panels ((A) and (B)) represent untreated and collagen stimulated, and ((C)–(F)) represent quercetin dose-dependent effects. (b) The bar graph shows summary of 4 independent experiments. (c) ATP release in response to agonist stimulation was performed as described in the “Materials and Methods.” (d) Platelets (3 × 10⁸/mL) were loaded with Fura-2/AM and preincubated with or without quercetin in the presence of 1 mM CaCl₂ for 2 min followed by thrombin (0.1 U/mL) stimulation for 5 min at 37°C and [Ca²⁺]_i levels were determined. Bar graphs show mean ± SEM of at least 4 independent experiments performed. *𝑃<0.05, **𝑃<0.01 or ***𝑃<0.001 versus agonist-activated control.