RED CELLS Dipyridamole inhibits sickling-induced cation fluxes in sickle red blood cells

Sickling-induced cation fluxes contribute to cellular dehydration of sickle red blood cells (SS RBCs), which in turn potentiates sickling. This study examined the inhibition by dipyridamole of the sicklinginduced fluxes of Na1, K1, and Ca11 in vitro. At 2% hematocrit, 10 mM dipyridamole inhibited 65% of the increase in net fluxes of Na1 and K1 produced by deoxygenation of SS RBCs. Sickle-induced Ca11 influx, assayed as 45Ca11 uptake in quin-2–loaded SS RBCs, was also partially blocked by dipyridamole, with a dose response similar to that of Na1 and K1 fluxes. In addition, dipyridamole inhibited the Ca11-activated K1 flux (via the Gardos pathway) in SS RBCs, measured as net K1 efflux in oxygenated cells exposed to ionophore A23187 in the presence of external Ca11, but this effect resulted from reduced anion conductance, rather than from a direct effect on the K1 channel. The degree of inhibition of sickling-induced fluxes was dependent on hematocrit, and up to 30% of dipyridamole was bound to RBC membranes at 2% hematocrit. RBC membrane content of dipyridamole was measured fluorometrically and correlated with sicklinginduced flux inhibition at various concentrations of drug. Membrane drug content in patients taking dipyridamole for other clinical indications was similar to that producing inhibition of sickling-induced fluxes in vitro. These data suggest that dipyridamole might inhibit sickling-induced fluxes of Na1, K1, and Ca11 in vivo and therefore have potential as a pharmacological agent to reduce SS RBC dehydration. (Blood. 2001;97:3976-3983)