Dapoxetine induces neuroprotective effects against glutamate-induced neuronal cell death by inhibiting calcium signaling and mitochondrial depolarization in cultured rat hippocampal neurons
Selective serotonin reuptake inhibitors (SSRIs) have an inhibitory effect on various ion channels including Ca2+ channels. We used fluorescent dye-based digital imaging, whole-cell patch clamping and cytotoxicity assays to examine whether dapoxetine, a novel rapid-acting SSRI, affect glutamate-induced calcium signaling, mitochondrial depolarization and neuronal cell death in cultured rat hippocampal neurons. Pretreatment with dapoxetine for 10 min inhibited glutamate-induced intracellular free Ca2+ concentration ([Ca2+]i) increases in a concentration-dependent manner (Half maximal inhibitory concentration=4.79 μM). Dapoxetine (5 μM) markedly inhibited glutamate-induced [Ca2+]i increases, whereas other SSRIs such as fluoxetine and citalopram only slightly inhibited them. Dapoxetine significantly inhibited the glutamate-induced [Ca2+]i responses following depletion of intracellular Ca2+ stores by treatment with thapsigargin. Dapoxetine markedly inhibited the metabotropic glutamate receptor agonist, (S)−3,5-dihydroxyphenylglycine-induced [Ca2+]i increases. Dapoxetine significantly inhibited the glutamate and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-induced [Ca2+]i responses in either the presence or absence of nimodipine. Dapoxetine also significantly inhibited AMPA-evoked currents. However, dapoxetine slightly inhibited N-methyl-D-aspartate (NMDA)-induced [Ca2+]i increases. Dapoxetine markedly inhibited 50 mM K+-induced [Ca2+]i increases. Dapoxetine significantly inhibited glutamate-induced mitochondrial depolarization. In addition, dapoxetine significantly inhibited glutamate-induced neuronal cell death and its neuroprotective effect was significantly greater than fluoxetine. These data suggest that dapoxetine reduces glutamate-induced [Ca2+]i increases by inhibiting multiple pathways mainly through AMPA receptors, voltage-gated L-type Ca2+ channels and metabotropic glutamate receptors, which are involved in neuroprotection against glutamate-induced cell death through mitochondrial depolarization.