Efffects of Fluoxetine on ATP-induced Calcium Signaling in PC12 Cells

Efffects of Fluoxetine 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 [<SUP>3</SUP>H]-inositol phosphates (IPs). Treatment with ATP (100μM) for 2 min induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increases. The ATP-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increases were significantly decreased by removal of extracellular Ca<SUP>2&#8290;</SUP> and treatment with the inhibitor of endoplasmic reticulum Ca<SUP>2&#8290;</SUP> ATPase thapsigargin (1μM). Treatment with fluoxetine for 5 min blocked the ATP-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increase concentration-dependently. Treatment with fluoxetine (30μM) for 5 min blocked the ATP-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increase following removal of extracellular Ca<SUP>2&#8290;</SUP> and depletion of intracellular Ca<SUP>2&#8290;</SUP> stores. While treatment with the L-type Ca<SUP>2&#8290;</SUP> channel antagonist nimodipine for 10 min inhibited the ATP-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increases significantly, treatment with fluoxetine alone blocked the ATP-induced responses. Treatment with fluoxetine also inhibited the 50 mM K<SUP>&#8290;</SUP>-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increases completely. However, treatment with fluoxetine did not inhibit the ATP-induced [<SUP>3</SUP>H]-IPs formation. Collectively, we conclude that fluoxetine inhibits ATP-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increases in PC12 cells by inhibiting both an influx of extracellular Ca<SUP>2&#8290;</SUP> and a release of Ca<SUP>2&#8290;</SUP> from intracellular stores without affecting IPs formation.