GSK3β antagonists enhance aggregation to PAR1 agonists. (A) Washed human platelets (2.5 × 10⁸/mL) were incubated for 2 hours with LiCl (20 mM), SB216763 (10 μM), or Tyrode buffer, then stimulated with human TRAP (PAR1 agonist) SFLLRN (5 μM), and aggregation was measured in an optical aggregometer. (B) Aggregation in response to varying concentrations of SFLLRN (1-10 μM) was measured as described in panel A. (WT, ○; LiCl (20 mM), ●; SB216763 (10 μM), ▲.) The results shown are the means (± SD) of 3 to 8 data points. The difference between LiCl and WT, or SB216763 and WT is statistically significant with **P < .01, *P < .05, unpaired Student t test. (C) Aggregation to 7 μM SFLLRN in the presence of the indicated concentrations (M) of LiCl or SB216763 was measured 3 to 16 times for each data point. Results were plotted and analyzed to fit a Sigmoidal dose-response in GraphPad Prizm to obtain the EC50s for each compound.