Fig. 6

P-glycoprotein transport function in hCMEC/D3 and RBE4 wildtype and MDR1-EGFP expressing cells by rhodamine 123 uptake assay. Cells were cultured in 6-well plates with or without doxycycline (dox) and intracellular accumulation of rhodamine 123 (Rho123) was assessed and reported as absolute fluorescence per mg protein in the presence or absence of the Pgp inhibitor tariquidar (A, C). Intracellular Rho123 accumulation negatively correlates with Pgp activity. Data are shown as means + SEM of three experiments; significant differences in intracellular Rho123 accumulation between cell types are marked by asterisks (P < 0.05). In B and D, the Pgp function was expressed by calculation of the multidrug resistance activity factor (MAF) according to Huber et al. ([40]; see Methods) as a quantitative measure of multidrug resistance. MAF values are presented as means + SEM of 3 replicates; statistical analysis was performed by one-way ANOVA followed by Bonferroni’s multiple comparisons test; significant differences compared to wildtype control cells (-dox) are indicated by asterisks (P < 0.05)