Effect of bisphenol A on Ca ²⁺ fluxes and viability in Madin-Darby canine renal tubular cells

The effect of the environmental contaminant, bisphenol A, on cytosolic free Ca ²⁺ concentrations ([Ca ²⁺]i) in Madin-Darby canine kidney (MDCK) cells is unclear. This study explored whether bisphenol A changed basal [Ca ²⁺]i levels in suspended MDCK cells by using fura-2 as a Ca ²⁺-sensitive fluorescent dye. Bisphenol A, at concentrations between 50 and 300 M, increased [Ca ²⁺]i in a concentration-dependent manner. The Ca ²⁺ signal was reduced, partly, by removing extracellular Ca ²⁺. Bisphenol A induced Mn ²⁺ influx, leading to quenching of fura-2 fluorescence, suggesting Ca ²⁺ influx. This Ca ²⁺ influx was inhibited by phospholipase A2 inhibitor aristolochic acid, store-operated Ca ²⁺ channel blockers nifedipine and SK&F96365, and protein kinase C inhibitor GF109203X. In Ca ²⁺-free medium, pretreatment with the mitochondrial uncoupler, carbonylcyanide m-chlorophenylhydrazone (CCCP), and the endoplasmic reticulum Ca ²⁺ pump inhibitors, thapsigargin or 2,5-di-tert-butylhydroquinone (BHQ), inhibited bisphenol Ainduced Ca ²⁺ release. Conversely, pretreatment with bisphenol A abolished thapsigargin (or BHQ)-and CCCP-induced [Ca ²⁺]i rise. Inhibition of phospholipase C with U73122 abolished bisphenol-induced [Ca ²⁺]i rise. Bisphenol A caused a concentration-dependent decrease in cell viability via apoptosis in a Ca ²⁺-independent manner. Collectively, in MDCK cells, bisphenol A induced [Ca ²⁺]i rises by causing phospholipase Cdependent Ca ²⁺ release from the endoplasmic reticulum and mitochondria and Ca ²⁺ influx via phospholipase A2, protein kinase Csensitive, store-operated Ca ²⁺ channels.