Figure 6.

PLCγ2 tyrosine phosphorylation is inhibited with highest potency by flavonoids with planar, hydroxylated C rings (quercetin) and metabolites with methylated B rings (tamarixetin). Washed human platelets (8 × 10⁸ cells·mL⁻¹) treated with 1 mM EGTA were incubated for 5 min with flavonoids (quercetin: A, B and apigenin: D), metabolites [tamarixetin: B, quercetin-3′-sulphate (Q-3′-S): C and quercetin-3-glucuronide (Q-3-G): C] or solvent control (DMSO 0.2% v/v). Platelets were stimulated with 25 µg·mL⁻¹ collagen for 90 s. PLCγ2 phosphotyrosine residues were detected before equivalent protein loading was verified by reprobing for PLCγ2. Tyrosine phosphorylation was expressed as a percentage of the DMSO-treated, collagen-stimulated control (100%). The bars represent the mean (n= 3) tyrosine phosphorylation for each treatment (±SEM). *P≤ 0.05, **P≤ 0.01 and ***P≤ 0.001 compared with the control (DMSO-treated, collagen-stimulated platelets).