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

Abstract

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 µM, 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.

Keywords::

• Bisphenol A
• Ca²⁺
• MDCK
• renal cells