Transfection of AQP9 in K562 cells. (A) In MTT assay, K562_EGFP-AQP9 showed an increase in As₂O₃ sensitivity compared with K562_EGFP-C2 cells (Student t test for each of the points analyzed). Note that the difference of As₂O₃ sensitivity between K562_EGFP-AQP9 and K562_EGFP cells widened with an increasing concentration of As₂O₃. NS indicates not significant. (B) In arsenic-uptake assay, K562_EGFP-AQP9 cells accumulated significantly more arsenic than K562_EGFP-C2 cells (Student t test for each of the points analyzed). Both lines showed a time-dependent increase in arsenic uptake.