Effect of fluoxetine on intracellular Ca2+ levels in bladder female transitional carcinoma (BFTC) cells

The effect of the antidepressant fluoxetine on Ca2+ signaling in cultured cells was largely unknown. The effect of various concentrations of fluoxetine on [Ca 2+] i in populations of bladder female transitional cancer (BFTC) cells was evaluated by using fura-2 as a Ca2+ probe. Fluoxetine increased [Ca 2+] i concentration dependently (20-100 microM) with an EC50 value of 30 microM. The response was inhibited by 50-60% on extracellular Ca2+ removal. In Ca2+ -free medium, pretreatment with 1 microM thapsigargin (an inhibitor of the endoplasmic reticulum Ca2+ pump) abolished 50 microM fluoxetine-induced Ca2+ release; whereas pretreatment with fluoxetine did not alter the thapsigargin-induced Ca2+ response. Addition of 3 mM Ca2+ increased [Ca 2+] i after pretreatment with 50 microM fluoxetine in Ca2+ -free medium, suggestive of fluoxetine-induced capacitative Ca2+ entry. Suppression of inositol 1,4,5-trisphosphate formation by 2 microM U73122 (a phospholipase C inhibitor) did not affect 50 microM fluoxetine-induced Ca2+ release. Collectively, this study shows that fluoxetine increased [Ca 2+] i in bladder cancer cells in a concentration-dependent fashion, by releasing Ca2+ from thapsigargin-sensitive Ca2+ stores in an IP3-independent manner, and by inducing Ca2+ influx from extracellular medium.