Effect of bisphenol A on Ca2+ fluxes and viability in Madin-Darby canine renal tubular cells

The effect of the environmental contaminant, bisphenol A, on cytosolic free Ca2+ concentrations ([Ca2+](i)) in Madin-Darby canine kidney (MDCK) cells is unclear. This study explored whether bisphenol A changed basal [Ca2+](i) levels in suspended MDCK cells by using fura-2 as a Ca2+-sensitive fluorescent dye. Bisphenol A, at concentrations between 50 and 300 mu M, increased [Ca2+](i) in a concentration-dependent manner. The Ca2+ signal was reduced, partly, by removing extracellular Ca2+. Bisphenol A induced Mn2+ influx, leading to quenching of fura-2 fluorescence, suggesting Ca2+ influx. This Ca2+ influx was inhibited by phospholipase A2 inhibitor aristolochic acid, store-operated Ca2+ channel blockers nifedipine and SK&F96365, and protein kinase C inhibitor GF109203X. In Ca2+-free medium, pretreatment with the mitochondrial uncoupler, carbonylcyanide m-chlorophenylhydrazone (CCCP), and the endoplasmic reticulum Ca2+ pump inhibitors, thapsigargin or 2,5-di-tert-butylhydroquinone (BHQ), inhibited bisphenol A-induced Ca2+ release. Conversely, pretreatment with bisphenol A abolished thapsigargin (or BHQ)- and CCCP-induced [Ca2+](i) rise. Inhibition of phospholipase C with U73122 abolished bisphenol-induced [Ca2+](i) rise. Bisphenol A caused a concentration-dependent decrease in cell viability via apoptosis in a Ca2+-independent manner. Collectively, in MDCK cells, bisphenol A induced [Ca2+](i) rises by causing phospholipase C-dependent Ca2+ release from the endoplasmic reticulum and mitochondria and Ca2+ influx via phospholipase A2-, protein kinase C-sensitive, store-operated Ca2+ channels.