Effect of capsazepine on [Ca 2+ ] i in MDCK renal tubular cells

The current study explored whether capsazepine changed basal cytosolic free Ca 2+ concentrations ([Ca 2+ ] i ) levels in suspended Madin Darby canine kidney (MDCK) cells cells by using fura‐2 as a Ca 2+ ‐selective fluorescent dye. At concentrations of 10–200 µM, capsazepine increased [Ca 2+ ] i in a concentration‐dependent manner. The Ca 2+ signal was partially reduced by 40% by removing extracellular Ca 2+ . Capsazepine induced Mn 2+ quench of fura‐2 fluorescence, indirectly implicating Ca 2+ entry. Capsazepine‐induced Ca 2+ influx was unchanged by L‐type Ca 2+ entry inhibitors and protein kinase C modulators [phorbol 12‐myristate 13‐acetate (PMA) and GF109203X]. In Ca 2+ ‐free medium, 100 µM capsazepine‐induced Ca 2+ release was substantially suppressed by pretreatment with thapsigargin (an endoplasmic reticulum Ca 2+ pump inhibitor). Pretreatment with capsazepine nearly abolished thapsigargin‐induced Ca 2+ release. Inhibition of phospholipase C with U73122 did not change capsazepine‐induced [Ca 2+ ] i rises. Collectively, in MDCK cells, capsazepine induced [Ca 2+ ] i rises by causing phospholipase C‐independent Ca 2+ release from the endoplasmic reticulum and Ca 2+ influx via non‐L‐type Ca 2+ channels. Drug Dev Res 72: 323–329, 2011. © 2010 Wiley‐Liss, Inc.