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 [Ca²⁺]_i in populations of bladder female transitional cancer (BFTC) cells was evaluated by using fura-2 as a Ca²⁺ probe. Fluoxetine increased [Ca²⁺]_i concentration dependently (20-100 μM) with an EC₅₀ value of 30 μM. The response was inhibited by 50-60% on extracellular Ca²⁺ removal. In CA²⁺-free medium, pretreatment with 1 μM thapsigargin (an inhibitor of the endoplasmic reticulum Ca²⁺ pump) abolished 50 μM fluoxetine-induced Ca²⁺ release; whereas pretreatment with fluoxetine did not alter the thapsigargin-induced Ca²⁺ response. Addition of 3 mM Ca²⁺ increased [Ca²⁺]_i after pretreatment with 50 μM fluoxetine in Ca²⁺-free medium, suggestive of fluoxetine-induced capacitative Ca²⁺ entry. Suppression of inositol 1,4,5-trisphosphate formation by 2 μM U73122 (a phospholipase C inhibitor) did not affect 50 μM fluoxetine-induced Ca²⁺ release. Collectively, this study shows that fluoxetine increased [Ca²⁺]_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.