Porcine choroid plexus cells in culture: expression of polarized phenotype, maintenance of barrier properties and apical secretion of CSF-components.

We have successfully cultured choroid plexus epithelial cells from porcine brain in pure form by the addition of cytosine arabinoside to the culture medium which prevented growth of other contaminating cells. We characterized the cells in culture by the presence of desmoplakin, fibronectin, thrombospondin, and the zonula occludens protein ZO-1 in comparison to frozen fractions of the isolated choroid plexus tissue. The cells in culture express those marker proteins and moreover exhibit a polarized phenotype which was expected from the presence of tight junction strands that correlate to an electrical resistance of 120 Ohm.cm2 measured across the cell monolayer on a permeable support. Permeability studies with fluorescein-labeled dextrans also indicate a biochemical tightness. The polarity of the cells is demonstrated by the presence of microvilli and cilia on the surface of the cultured cells as well as by the laser scanning microscopic determination of the apical localization of the ZO-1-protein and the Na+K(+)-ATPase. Thrombospondin and fibronectin were found to be localized at the basolateral membrane side. The cells in culture secrete medium containing prealbumin predominantly into the apical compartment which demonstrates that they are able to release medium containing CSF-proteins and therefore verifies the usefulness of this in vitro model.