Dipyridamole fluorescence in RBC ghost membranes.

Intact RBCs at 2% hematocrit were exposed to dipyridamole at the indicated nominal concentrations, and sickling-induced Na⁺influx was measured. Remaining cells were washed and ghosts prepared as described in “Materials and methods.” Fluorescence measurements were made at equal concentrations of membrane protein and identical fluorometer settings. Three experiments in different donors are shown as different symbols. (A) Fluorescence measurements (arbitrary units) in RBC ghosts as a function of nominal dipyridamole concentration in RBC incubation. (B) Sickling-induced Na⁺ influx as a function of nominal dipyridamole concentration. (C) Sickling-induced Na⁺ influx as a function of ghost fluorescence. Arrows represent fluorescence in ghosts derived from RBCs of patients taking dipyridamole.