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 (50-150 μM) 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 20-40 μM, 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.