Organic cation transport in rat choroid plexus cells studied by fluorescence microscopy

Quinacrine uptakeand distribution were studied in a primary culture of rat choroidplexus epithelial cells using conventional and confocal fluorescencemicroscopy and image analysis. Quinacrine rapidly accumulated in cells,with steady-state levels being achieved after 10-20 min. Uptakewas reduced by other organic cations, e.g., tetraethylammonium (TEA),and by KCN. Quinacrine fluorescence was distributed in two cytoplasmiccompartments, one diffuse and the other punctate. TEA effluxexperiments indicated that more than one-half of intracellular organiccation was in a slowly emptying compartment. The protonophore monensinboth emptied that TEA compartment and abolished punctate quinacrinefluorescence, suggesting that a large fraction of total intracellularorganic cation was sequestered in acidic vesicles, e.g., endosomes.Finally, quinacrine-loaded vesicles were seen to move within thecytoplasm and to abruptly release their contents at the blood side ofthe cell; the rate of release was greatly reduced by the microtubule disrupter nocodazole.