Mean TEER values (blue curve) and C
values (black curve) recorded real-time by the CellZscope system of four human brain capillary endothelial cell lines grown on 24-well tissue culture inserts. Black arrows indicate the time when the permeability assay with Na-F was performed (for resulting Papp values see Figures 7A and B). For hCMEC/D3 and TY10, the permeability assay was performed at TEER values in the range of 10 Ωcm2 (hCMEC/D3: *cultured with initial medium (A), **cultured with growth medium 20% FBS (B). For hBMEC, the assay was carried out at TEER values in the range of 30 Ωcm2. TEER values after the assay were in the same range or even higher as before, suggesting that cell layers were robust during the experiment and barrier integrity was maintained (A-D). For each of the three cell lines, CCL values were in the acceptable range of 0.5-5.0 μF/cm2, indicating that cells were confluent. BB19 cell line (E) yielded very low TEER values in the range of 5 Ωcm2. Since CCL values were drastically increasing after 55 h, the experiment was stopped. BB19 cells were not included into permeability studies with Na-F and LY due to their low TEER. All experiments were performed with Greiner Bio-one® inserts (transparent PET membrane, 3.0 μm pore size, 0.6 × 106 pores/cm2, n = 2–5).