Ca2+ Signaling and Cell Death Induced by Protriptyline in HepG2 Human Hepatoma Cells

The effect of protriptyline on Ca2+ physiology in human hepatoma is unclear. This study explored the effect of protriptyline on [Ca2+](i) and cytotoxicity in HepG2 human hepatoma cells. Protriptyline (50-150M) evoked [Ca2+](i) rises. The Ca2+ entry was inhibited by removal of Ca2+. Protriptyline-induced Ca2+ entry was confirmed by Mn2+-induced quench of fura-2 fluorescence. Except nifedipine, econazole, SKF96365, GF109203X, and phorbol 12-myristate 13 acetate did not inhibit Ca2+ entry. Treatment with the endoplasmic reticulum Ca2+ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) inhibited 40% of protriptyline-induced response. Treatment with protriptyline abolished BHQ-induced response. Inhibition of phospholipase C (PLC) suppressed protriptyline-evoked response by 70%. At 20-40M, protriptyline killed cells which was not reversed by the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid-acetoxymethyl ester (BAPTA/AM). Together, in HepG2 cells, protriptyline induced [Ca2+](i) rises that involved Ca2+ entry through nifedipine-sensitive Ca2+ channels and PLC-dependent Ca2+ release from endoplasmic reticulum. Protriptyline induced Ca2+-independent cell death.