Fendiline-evoked [Ca2+]i rises and non-Ca2+-triggered cell death in human oral cancer cells

The effect of fendiline on cytosolic free Ca2+ concentrations ([Ca2+](i)) and proliferation has not been explored in human oral cancer cells. This study examined whether fendiline altered Ca2+ levels and caused cell death in OC2 human oral cancer cells. [Ca2+](i) and cell viability were measured using the fluorescent dyes fura-2 and WST-1, respectively. Fendiline at concentrations above 10 mu M increased [Ca2+](i) in a concentration-dependent manner. The Ca2+ signal was reduced partly by removing extracellular Ca2+. The fendiline-induced Ca2+ influx was sensitive to blockade of L-type Ca2+ channel blockers. In Ca2+-free medium, after pretreatment with 50 mu M fendiline, 1 mu M thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor)-induced [Ca2+](i) rises were inhibited; and conversely, thapsigargin pretreatment nearly abolished fendiline-induced [Ca2+](i) rises. Inhibition of phospholipase C with 2 mu M U73122 did not change fendiline-induced [Ca2+](i) rises. At concentrations between 5 and 25 mu M, fendiline killed cells in a concentration-dependent manner. The cytotoxic effect of 15 mu M fendiline was not reversed by prechelating cytosolic Ca2+ with BAPTA/AM. Collectively, in OC2 cells, fendiline induced [Ca2+](i) rises by causing Ca2+ release from the endoplasmic reticulum and Ca2+ influx from L-type Ca2+ channels. Furthermore, fendiline-caused cytotoxicity was not via a preceding [Ca2+](i) rise.