Cytotoxicity study
MDCK-hOCTN1, MDCK-hOCTN2, MDCK-hOCT2, MDCK-hMRP2 and mock cells in the logarithmic growth phase were digested and collected. The cells were resuspended in fresh medium, adjusted to a cell density of 4.0 × 104 /mL, and seeded in 96-well cell plates at 0.2 mL /well. After the above cells and primary DRG cells were cultured for 24 h, the cells were treated with 40 μM OXA in the absence or presence of L-THP for another 48 h, a part of the medium was collected for the measurement of lactate dehydrogenase (LDH) activity using the LDH assay kit, and the cell viability was evaluated by the MTT assay (Tu & Li et al., 2014; Li & Song et al., 2016).