Dipyridamole binding to intact RBCs.

Dipyridamole fluorescence at 480 nm with excitation at 293 nm was assayed in supernatants of 2% RBC suspensions after the addition of the indicated concentrations of drug. The standard curve (●) was generated by means of supernatants obtained by centrifugation prior to exposure to drug, with subsequent addition of dipyridamole; this served as a control for possible quenching by small amounts of hemoglobin in the supernatant. Intact RBCs (▪) and red ghosts (▴) removed dipyridamole from the suspensions, as evidenced by reduced fluorescence in supernatants at all dipyridamole concentrations. A single experiment, representative of 2 others, is shown.