Abstract

The objective of this study was to develop and evaluate a primary culture system for choroid plexus epithelial cells as an in vitro model for studying organic cation transport. Cells were dispersed from choroid plexus of neonatal rats by enzymatic digestion and grew as differentiated monolayers when plated on solid or permeable support. Electron microscopy showed that cultured cells were morphologically similar to intact choroid plexus epithelium, having apical tight junctions between cells, numerous mitochondria, basal nuclei and apical microvilli and cilia. As previously demonstrated for intact choroid plexus, immunocytochemistry showed that Na⁺,K⁺-ATPase was localized to the apical membrane, and GLUT-1, the facilitative glucose transporter, was localized to the basolateral membrane of cultured cells. Apical transport of l-proline by cultured cells was mediated by a sodium-dependent, electrogenic process, as in whole tissue.¹⁴C-Tetraethylammonium (TEA), a prototypic organic cation, was accumulated by isolated choroid plexus in a time-dependent manner; uptake was inhibited by tetrapentyl-ammonium (TePA). In cultured cells, apical TEA transport was mediated by a saturable process coupled to cellular metabolism. Unlabeled TEA and other organic cations (TePA, N¹-methylnicotinamide and mepiperphenidol) inhibited TEA transport; the organic anion, p-aminohippurate, had no effect. Finally, TePA-sensitive transport of ¹⁴C-TEA was stimulated after preloading the cells with unlabeled TEA. Based on the morphological, biochemical and functional properties of these cultured cells, we conclude that this primary culture system should be an excellent in vitro model for experimental characterization of choroid plexus function.