Tamoxifen-induced (Ca(2+))(i) rise and apoptosis in corneal epithelial cells.

摘要

The effect of tamoxifen on cytosolic free Ca(2+) concentrations ([Ca(2+)](i)) and viability has not been explored in corneal epithelial cells. This study examined whether tamoxifen altered [Ca(2+)](i) and viability in SIRC corneal epithelial cells. Tamoxifen at concentrations >/=1muM increased [Ca(2+)](i) in a concentration-dependent manner with an EC(50) value of 6muM. The Ca(2+) signal was reduced substantially by removing extracellular Ca(2+). Tamoxifen induced Mn(2+) quench of fura-2 fluorescence implicating Ca(2+) influx. The Ca(2+) influx was insensitive to Ca(2+) entry inhibitors and protein kinase C modulators. After pretreatment with thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor), tamoxifen-induced [Ca(2+)](i) rises were abolished; conversely, tamoxifen pretreatment abolished thapsigargin-induced [Ca(2+)](i) rises. Inhibition of phospholipase C with U73122 did not change the [Ca(2+)](i) rises. At concentrations of 5-30muM, tamoxifen killed cells in a concentration-dependent manner. The cytotoxic effect of 15muM tamoxifen was not reversed by prechelating cytosolic Ca(2+) with BAPTA/AM. Apoptosis was induced by 5-30muM tamoxifen. Tamoxifen (30muM) did not induce production of reactive oxygen species (ROS). Collectively, in SIRC cells, tamoxifen induced [Ca(2+)](i) rises by causing Ca(2+) release from the endoplasmic reticulum in a phospholipase C-independent manner, and Ca(2+) influx via unknown pathways. Tamoxifen-caused cytotoxicity was partly mediated by a Ca(2+)-independent apoptotic pathway.