Effects of flouxetine on ATP-induced calcium signaling in PC12 cells

Fluoxetine, a widely used anti-depressant compound, has several additional effects, including blockade of voltage-gated ion channels. We examined whether fluoxetine affects ATP-induced calcium signaling in PC12 cells by using fura-2-based digital calcium imaging and assay for [³H]-inositol phosphates (IPs). Treatment with ATP (100 μM for 2 min induced [Ca²⁺]_i increases. The ATP-induced [Ca²⁺]_i increases were significantly decreased by removal of extracellular Ca²⁺ and treatment with the inhibitor of endoplasmic reticulum Ca²⁺ ATPase thapsigargin (1 μM). Treatment with fluoxetine for 5 min blocked the ATP-induced [Ca²⁺]_i increase concentration-dependently. Treatment with fluoxetine (30 μM) for 5 min blocked the ATP-induced [Ca²⁺]_i increase following removal of extracellular Ca²⁺ and depletion of intracellular Ca²⁺ stores. While treatment with the L-type Ca²⁺ channel antagonist nimodipine for 10 min inhibited the ATP-induced [Ca²⁺]_i increases significantly, treatment with fluoxetine alone blocked the ATP-induced responses. Treatment with fluoxetine also inhibited the 50 mM K⁺-induced [Ca²⁺]_i increases completely. However, treatment with fluoxetine did not inhibit the ATP-induced [³H]-IPs formation. Collectively, we conclude that fluoxetine inhibits ATP-induced [Ca²⁺]ⁱ increases in PC12 cells by inhibiting both an influx of extracellular Ca²⁺ and a release of Ca²⁺ from intracellular stores without affecting IPs formation.