Econazole-Evoked [Ca2+](i) Rise and Non-Ca2+-Triggered Cell Death in Rabbit Corneal Epithelial Cells (SIRC)

The effects of econazole, an antifungal drug applied for treatment of keratitis and mycotic corneal ulcer, on cytosolic-free Ca2+ concentrations ([Ca2+](i)) and viability of corneal cells was examined by using SIRC rabbit corneal epithelial cells as model. [Ca2+] i and cell viability were measured by using the fluorescent dyes fura-2 and WST-1, respectively. Econazole at concentrations >= 1 mu M increased [Ca2+](i) in a concentration-dependent manner. The Ca2+ signal was reduced partly by removing extracellular Ca2+. The econazole-induced Ca2+ influx was insensitive to L-type Ca2+ channel blockers and protein kinase C modulators. In Ca2+-free medium, after pretreatment with 20 mu M econazole, [Ca2+](i) rises induced by 1 mu M thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor) were abolished. Conversely, thapsigargin pretreatment also abolished econazole-induced [Ca2+](i) rises. Inhibition of phospholipase C with 2 mu M U73122 did not change econazole-induced [Ca2+](i) rises. At concentrations between 10 and 80 mu M, econazole killed cells in a concentration-dependent manner. The cytotoxic effect of 20 mu M econazole was not reversed by prechelating cytosolic Ca2+ with BAPTA. This shows that in SIRC cells econazole induces [Ca2+](i) rises by causing Ca2+ release from the endoplasmic reticulum and Ca2+ influx from unknown pathways. Econazole-caused cytotoxicity was independent from a preceding [Ca2+](i) rise.