Effect of capsazepine on cytosolic Ca(2+) 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 Ca(2+) concentrations (Ca(2+)](i)) and cytotoxicity was investigated by using fura-2 and tetrazolium, respectively. Capsazepine caused a rapid rise in Ca(2+)](i) in a concentration-dependent manner with an EC(50) value of 75 microM. Capsazepine-induced Ca(2+)](i) rise was reduced by 60% by removal of extracellular Ca(2+), suggesting that the capsazepine-induced Ca(2+)](i) rise was contributed by extracellular Ca(2+) influx and intracellular Ca(2+). Consistently, the capsazepine (200 microM)-induced Ca(2+)](i) rise was decreased by La(3+) by half. In Ca(2+)-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca(2+)-ATPase, caused a monophasic Ca(2+)](i) rise, after which the effect of capsazepine on Ca(2+)](i) was inhibited by 80%. Conversely, pretreatment with capsazepine partly reduced thapsigargin-induced Ca(2+)](i) rise. U73122, an inhibitor of phospholipase C, abolished histamine (an inositol 1,4,5-trisphosphate-dependent Ca(2+) mobilizer)-induced, but not capsazepine-induced, Ca(2+)](i) rise. These findings suggest that in human PC3 prostate cancer cells, capsazepine increases Ca(2+)](i) by evoking Ca(2+) influx and releasing Ca(2+) from the endoplasmic reticulum via a phospholiase C-independent manner. Overnight incubation with capsazepine (200 microM) killed 37% of cells, which could not be prevented by chelating intracellular Ca(2+) with BAPTA.