Transport of [H-3]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 cati on 1-methyl-4-phenylpyridinium (MPP+) in an immortalized cell line of rat c apillary cerebral endothelial cells (RBE 4). Verapamil (100 muM) and rhodam ine123 (10 muM), and decynium22 (2 muM) and corticosterone (100 muM) reduce d cellular accumulation of [H-3]MPP+ applied from the luminal and abluminal cell border, respectively. When cells were grown on plastic supports, [H-3 ]MPP+ accumulated in the cells. The kinetic parameters of the saturable com ponent were: K-m = 25 muM and V-max = 246 pmol per mg protein and 15 min. A selective organic anion transport inhibitor and selective inhibitors of th e L- and A-type amino acid transporters did not affect [H-3]MPP+ uptake. Up take of [H-3]MPP+ was Na+-independent and metabolic energy-, pH- and potent ial-dependent. It was inhibited by several organic cations (e.g., verapamil , quinidine, daunomycin, dopamine) but not by others (cimetidine, tetraethy lammonium, N-methylnicotinamide). In conclusion, [H-3]MPP+ is efficiently t ransported by RBE 4 cells in both abluminal-to-luminal and luminal-to-ablum inal directions. Absorption of [H-3]MPP+ seems to occur through a carrier-m ediated mechanism belonging to the amphiphilic solute facilitator (ASF) fam ily of transporters, but distinct from the known members of this family.