Effect of Fluoxetine on [Ca2+]i and Cell Viability in OC2 Human Oral Cancer Cells

Fluoxetine is a serotonin-specific reuptake inhibitor that has been used as an antidepressant. This study examined the effect of fluoxetine on cytosolic free Ca2+ concentrations ([Ca2+](i)) and viability in OC2 human oral cancer cells. The Ca2+-sensitive fluorescent dye fura-2 was used to measure [Ca2+](i), and the water soluble tetrazolium (WST-1) regent was used to measure viability. Fluoxetine-induced [Ca2+](i) rises concentration-dependently. The response was reduced by half by removing extracellular Ca2+. Fluoxetine-induced Ca2+ entry was enhanced by activation of protein kinase C (PKC) with phorbol 12-myristate 13 acetate (PMA) but was inhibited by inhibition of the enzyme with GF109203X. In Ca2+-free medium, treatment with the endoplasmic reticulum Ca2+ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) or thapsigargin abolished fluoxetine-evoked [Ca2+](i) rise. Conversely, treatment with fluoxetine inhibited BHQ/thapsigargin-evoked [Ca2+](i) rise. Inhibition of phospholipase C (PLC) with U73122 abolished fluoxetine-induced [Ca2+](i) rise. At 20-80 mu M, fluoxetine decreased cell viability concentration-dependently, which was not altered by chelating cytosolic Ca2+ with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA/AM). At 20-60 mu M, fluoxetine induced apoptosis as detected by annexin V/propidium iodide (PI) staining. Together, in OC2 cells, fluoxetine induced [Ca2+](i) rises by evoking PLC-dependent Ca2+ release from the endoplasmic reticulum and Ca2+ entry via PKC-regulated mechanisms. Fluoxetine also caused Ca2+-independent apoptosis.