Fig. 4.

Pgp is functional in hCMEC/D3 cells as indicated by the effect of the Pgp inhibitor tariquidar (TQ; 0.5 µM) in the Rho123 uptake assay, in which alterations in Pgp efflux are indirectly measured by determining intracellular concentrations of the Pgp substrate Rho123. Data are shown as mean ± SEM of six experiments. Significant differences between treatments are indicated by asterisk (P < 0.0001). a Shows data from the Rho123 uptake assay in nontransduced (WT) hCMEC/D3 cells in the absence or presence of doxycycline (Dox). Doxycycline (1 µg/mL) did not alter the functionality of Pgp. Tariquidar significantly increased the uptake of Rho123 in WT cells both in the absence and presence of doxycycline to the same extent. b Shows data from the Rho123 uptake assay in transduced hCMEC/D3-Cldn5-YFP cells in the absence or presence of Dox. Again, Dox (1 µg/mL) did not alter the functionality of Pgp. Tariquidar significantly increased the uptake of Rho123 in the transduced cells both in the absence and presence of Dox to the same extent. Consistent with the similar expression of Pgp in the two cell lines (see Fig. 2i), the functionality of Pgp was comparable in hCMEC/D3-WT and hCMEC/D3-Cldn5-YFP cells