Transport Characteristics of Ribavirin in Human Erythrocyte Membrane Vesicles

Abstract

Transport characteristics of ribavirin in human erythrocytes were evaluated using rightside–out membrane vesicles (ROVs) prepared from fresh blood, and compared with those in intact erythrocytes. [3H]Ribavirin uptake by ROVs at 23 ℃ was fairly rapid, and reached equilibrium at about 30 sec. The uptake of [3H]ribavirin by ROVs showed saturation kinetics with the Km value of 1.9 mM. The uptake by ROVs was inhibited by uridine (a typical substrate of equilibrative nucleoside transporter ENT1), S–(4–nitrobenzyl)–6–thioinosine (a specific inhibitor of ENT1), and dipyridamole (an inhibitor of ENT1). These characteristics of [3H]ribavirin transport in ROVs were similar to those observed in intact erythrocytes, though the affinity of [3H]ribavirin to the transport system and sensitivity to various inhibitors were lower in ROVs. Next, the interaction of ribavirin with ATP–dependent efflux transporters was evaluated using inside–out membrane vesicles (IOVs). Ribavirin weakly inhibited ATP–dependent uptake of methotrexate by multidrug resistance-associated protein (MRP) 4, but not the uptake of 5–(and 6)–carboxy–2’, 7’–dichlorofluorescein by MRP5, by IOVs. However, ATP–dependent uptake of [3H]ribavirin by IOVs was not observed. These results suggest that ribavirin is transported by ENT1 across human erythrocyte membranes, while ATP–dependent efflux transporters would not be involved in ribavirin transport.