Pretreatment with 100 µM TMP or 10 mM NAC efficiently reversed arsenic-induced mitochondrial dysfunction in HK-2 cells. a, b Arsenic decreased mitochondrial membrane potential in HK-2 cells, while TMP and NAC prevented such a down-regulation. c, d Arsenic-induced mitochondrial dysfunction was verified by a decreased cytochrome c oxidase (Cox) histochemical staining. e, f Succinate dehydrogenase histochemical staining. Values are mean ± SD (n = 3), *p < 0.05 versus Con, **p < 0.01 versus Con