GSAO rapidly enters the activated platelet subpopulation via an organic anion-transporting polypeptide. (A) The kinetics of labeling of stimulated platelets with GSAO-AF647 was measured by time-lapse flow cytometry. Flow plots are representative of n ≥ 3 separate experiments, and bars and data points are from n ≥ 3 separate experiments. *P < .05; ****P < .0001. (B-C) Washed human platelets were stimulated with thrombin (0.1 U/mL) and collagen (5 µg/mL), incubated with 0 to 200 µM DIDS for 10 minutes, and then exposure of P-selectin and labeling with GSAO-AF647 were measured by flow cytometry. DIDS inhibited labeling of P-selectin⁺ activated platelets at a half-maximal concentration of ∼30 µM. The data points and errors are the mean ± range of 1 to 5 experiments.