Interaction of dipyridamole, a nucleoside transport inhibitor, with the renal transport of organic cations by LLCPK1 cells.

Dipyridamole is a well-known inhibitor of nucleoside transport by various cell membranes and is frequently used in in vitro studies that characterize nucleoside transport properties. Because interactions between the renal transport of organic cations and nucleosides have previously been suggested, we studied the effect of dipyridamole on the renal transport of the typical organic cations cimetidine and N1-methylnicotinamide by LLCPK1 monolayer cells grown on a permeable support. [14C]Mannitol was used to correct for extracellular flux. Basolateral to apical transcellular flux (transepithelial flux-extracellular flux) of [3H]cimetidine was significantly reduced by the monolayer cells (90%) in the presence of 50 microM dipyridamole. In addition, the effect of dipyridamole on cimetidine renal transport was dose dependent (IC50 = 7.7 microM). The dipyridamole inhibitory effect was nearly comparable with the effect of 1 mM quinine (a typical organic cation transport inhibitor), which led to 95% inhibition of cimetidine renal transport over time. The dipyridamole effect on N1-methylnicotinamide renal transport was less potent. The effect of 1 mM of typical probes of the nucleoside transporters (i.e., thymidine, adenosine, uridine) and the effect of 100 nM of another nucleoside transport inhibitor, dilazep, were also studied on cimetidine transport by LLCPK1 monolayer cells. These compounds did not exert any significant effect. These results suggest that dipyridamole, a widely used nucleoside transport inhibitor, is also an inhibitor of organic cation renal transport and they alert us to possible interactions between the renal transport of nucleosides and organic cations. This finding also has relevance to the interpretation of in vitro studies using this agent as a nucleoside membrane transport inhibitor.