HepG2 cells were pre-incubated with drug-free HBSS or HBSS containing 0.125, 0.25, 0.5, 1, or 2 μM CCCP at 37°C for 20 min, then equal volume of HBSS containing 20 μM berberine or 6 μg/ml Rho123 was added and the cells were further incubated at 37°C for 0.5 h. After incubation, the cells were washed three times with chilled PBS and harvested by trypsinisation. The cells were stored in chilled PBS and the concentration of berberine in the cells was quantified by flow cytometry analysis with excitation at 488 nm and emission at 530 nm. * indicates P<0.05 while ** indicates P<0.01 versus groups that treated without CCCP.