Effects of CSE on ABC efflux transporter expression and functionality in hCMEC/D3 cell line. Cells were exposed to nicotine (100 ng/mL) or CSE derived from 3R4F or ULN cigarettes. a P-gp efflux activity was determined by intracellular accumulation of rhodamine123 (a P-gp substrate) efflux, as an indirect correlate of P-gp activity n = 3/condition and replicated twice. b Transcriptome analysis of ABC efflux transporters, ABCB1 (P-gp) and ABCC4 (MRP4) following treatment (n = 6 biological replicates); c RT-PCR analysis of mRNA expression of P-gp and ABCC4 in hCMEC/D3 cells (n = 6 biological replicates); western blot analysis of transporter protein expression (n = 6 biological replicates). Representative western blots were shown with actin as a loading control. Data were expressed as mean ± SEM (fold change over control). *p < 0.05, **p < 0.01, vs. control.