OXA exhibited the highest toxicity and accumulation in MDCK-hOCT2 cells
To confirm the roles of OCT2, OCTN1, and OCTN2 in the uptake of OXA, we compared OXA-induced toxicity in transporter-transfected MDCK cells. Our results revealed that the order of sensitivity to OXA was MDCK-hOCT2 (LD50: 3.3±0.7 μM) < MDCK-hOCTN1 (LD50: 32.5±1.1 μM) < MDCK-hOCTN2 ≈ mock cells (LD50> 100 μM) (Figure 1a ). We further showed that the cellular accumulation of OXA in the MDCK-hOCT2 and MDCK-hOCTN1 cells were 5.4 and 2.0 folds that in the mock cells (Figure 1b ), respectively. The above results imply that OCT2 and OCTN1 but not OCTN2 contribute to the uptake of OXA, and OCT2 plays the most crucial role.