We found that the induced ciBECs highly expressed polarized efflux transporters, such as PGP, BCRP, and MRPs. To define the biological function of these high expressions, we first examined PGP function using rhodamine-123, a cell-permeable PGP substrate. ECs and HUVEC showed about 1.2-fold increase and hCMEC/D3 about 2-fold increase in rhodamine-123 accumulation in the presence of verapamil, a PGP inhibitor. Notably, cell accumulation of rhodamine-123 in ciBECs was significantly increased approximately 2.5-fold with verapamil, demonstrating the functional PGP efflux activity of ciBECs (Figures 6A and S5A–S5C).
