The mitochondrial membrane potential was measured in HK2 cells seeded at a density of 105 cells per well on a 24-well plate, as previously described [29 (link)]. Briefly, tetramethylrhodamine, ethyl ester (TMRE; Abcam, Cambridge, MA, USA) (20 nM) was added to the cells and incubated for 30 minutes. After washing three times with 500 ml of phsphate buffered saline/0.2% fetal bovine serum three-times, the cells were read using a FilterMax F3 multimode microplate reader (Molecular Devices, Sunnyvale, CA, USA) at excitation and emission wavelengths of 549 nm and 575 nm, respectively.