Tamoxifen-induced [Ca2+]i rise and apoptosis in corneal epithelial cells

The effect of tamoxifen on cytosolic free Call concentrations ([Ca-i(2+])) and viability has not been explored in corneal epithelial cells. This study examined whether tamoxifen altered [Ca2+](i) and viability in SIRC corneal epithelial cells. Tamoxifen at concentrations >= 1 mu M increased [Ca2+], in a concentration-dependent manner with an EC50 value of 6 mu W. The Ca2+ signal was reduced substantially by removing extracellular Ca2+. Tamoxifen induced Mn2+ quench of fura-2 fluorescence implicating Ca2+ influx. The Call influx was insensitive to Ca2+ entry inhibitors and protein kinase C modulators. After pretreatment with thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor), tamoxifen-induced [Ca2+](i) rises were abolished: conversely, tamoxifen pretreatment abolished thapsigargin-induced [Ca2+](i) rises. Inhibition of phospholipase C with U73122 did not change the [Ca2+](i) rises. At concentrations of 5-30 mu M. tamoxifen killed cells in a concentration-dependent manner. The cytotoxic effect of 15 mu M tamoxifen was not reversed by prechelating cytosolic Ca2+ with BAPTA/AM. Apoptosis was induced by 5-30 mu M tamoxifen. Tamoxifen (30 mu M) did not induce production of reactive oxygen species (ROS). Collectively, in SIRC cells, tamoxifen induced [Ca2+](i) rises by causing Ca2+ release from the endoplasmic reticulum in a phospholipase C-independent manner, and Ca2+ influx via unknown pathways. Tamoxifen-caused cytotoxicity was partly mediated by a Ca2+-independent apoptotic pathway. (C) 2008 Elsevier Ireland Ltd. All rights reserved.