Effect of capsazepine on cytosolic Ca2+ levels and proliferation of human prostate cancer cells

Capsazepine has been widely used as a selective antagonist of vanilloid type 1 receptors; however, its other in vitro effect on most cell types is unknown. In human PC3 prostate cancer cells, the effect of capsazepine on intracellular Ca2+ concentrations ([Ca2+]i) and cytotoxicity was investigated by using fura-2 and tetrazolium, respectively. Capsazepine caused a rapid rise in [Ca2+]i in a concentration-dependent manner with an EC50 value of 75 μM. Capsazepine-induced [Ca2+]i rise was reduced by 60% by removal of extracellular Ca2+, suggesting that the capsazepine-induced [Ca2+]i rise was contributed by extracellular Ca2+ influx and intracellular Ca2+. Consistently, the capsazepine (200 μM)-induced [Ca2+]i rise was decreased by La3+ by half. In Ca2+-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+-ATPase, caused a monophasic [Ca2+]i rise, after which the effect of capsazepine on [Ca2+]i was inhibited by 80%. Conversely, pretreatment with capsazepine partly reduced thapsigargin-induced [Ca2+]i rise. U73122, an inhibitor of phospholipase C, abolished histamine (an inositol 1,4,5-trisphosphate-dependent Ca2+ mobilizer)-induced, but not capsazepine-induced, [Ca2+]i rise. These findings suggest that in human PC3 prostate cancer cells, capsazepine increases [Ca2+]i by evoking Ca2+ influx and releasing Ca2+ from the endoplasmic reticulum via a phospholiase C-independent manner. Overnight incubation with capsazepine (200 μM) killed 37% of cells, which could not be prevented by chelating intracellular Ca2+ with BAPTA.