Influence of retinoic acid (ATRA) on Rh123 efflux from the parental and cells RARα transfected cells. ATRA (5 μM) was added to cell cultures 24 h after seeding for 48 h. Than cells were loaded with 5 μg/ml Rh123 for 10 min at 37°C, than washed twice with cold PBS, and incubated for 30 min in dye-free medium at 37°C. After the completion of incubation, cell were washed twice with cold PBS. Cell fluorescence was measured on a flow cytometer FACScan (Becton Dikinson, USA). Each measurement counted 5000 events. Non-viable cells were gated out of the analysis on the basis of side scatter. This figure is representative of 2 separate experiments.