Transport of [3H]MPP+ in an immortalized rat brain microvessel endothelial cell line (RBE 4).

The aim of this study was to characterize the transport of the organic cation 1-methyl-4-phenylpyridinium (MPP+) in an immortalized cell line of rat capillary cerebral endothelial cells (RBE 4). Verapamil (100 microM) and rhodamine 123 (10 microM), and decynium22 (2 microM) and corticosterone (100 microM) reduced cellular accumulation of [3H]MPP+ applied from the luminal and abluminal cell border, respectively. When cells were grown on plastic supports, [3H]MPP+ accumulated in the cells. The kinetic parameters of the saturable component were: Km=25 microM and Vmax=246 pmol per mg protein and 15 min. A selective organic anion transport inhibitor and selective inhibitors of the L- and A-type amino acid transporters did not affect [3H]MPP+ uptake. Uptake of [3H]MPP+ was Na+-independent and metabolic energy-, pH- and potential-dependent. It was inhibited by several organic cations (e.g., verapamil, quinidine, daunomycin, dopamine) but not by others (cimetidine, tetraethylammonium, N-methylnicotinamide). In conclusion, [3H]MPP+ is efficiently transported by RBE 4 cells in both abluminal-to-luminal and luminal-to-abluminal directions. Absorption of [3H]MPP+ seems to occur through a carrier-mediated mechanism belonging to the amphiphilic solute facilitator (ASF) family of transporters, but distinct from the known members of this family.