Amitriptyline modulated Ca2+ signaling and induced Ca2+-independent cell viability in human osteosarcoma cells

Amitriptyline is a widely used tricyclic antidepressant, which acts primarily as a serotonin-norepinephrine reuptake inhibitor. This study examined the effect of amitriptyline on Ca2+ homeostasis and its related mechanism in MG63 human osteosarcoma cells. Amitriptyline evoked cytosolic-free Ca2+ concentrations ([Ca2+](i)) rises concentration dependently. Amitriptyline-evoked Ca2+ entry was confirmed by Mn2+-induced quench of fura-2 fluorescence. This entry was inhibited by Ca2+ entry modulators nifedipine, econazole, SKF96365, the protein kinase C (PKC) activator phorbol 12-myristate 13 acetate but was not affected by the PKC inhibitor GF109203X. In Ca2+-free medium, treatment with the endoplasmic reticulum Ca2+ pump inhibitor thapsigargin (TG) inhibited amitriptyline-evoked [Ca2+](i) rises by 95%. Conversely, treatment with amitriptyline abolished TG-evoked [Ca2+](i) rises. Inhibition of phospholipase C (PLC) with U73122 inhibited amitriptyline-evoked [Ca2+](i) rises by 70%. Amitriptyline killed cells at 200-500 M in a concentration-dependent fashion. Chelating cytosolic Ca2+ with 1,2-bis(2-aminophenoxy)ethane-N, N, N, N-tetraacetic acid/AM did not reverse amitriptyline-induced cytotoxicity. Collectively, our data suggest that in MG63 cells, amitriptyline induced [Ca2+](i) rises by evoking PLC-dependent Ca2+ release from the endoplasmic reticulum and Ca2+ entry via PKC-regulated store-operated Ca2+ entry. Amitriptyline also induced Ca2+-disassociated cell death.