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

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