Effect of nortriptyline on cytosolic Ca²⁺ regulation and viability in PC3 human prostate cancer cells

The effect of nortriptyline, a tricyclic antidepressant, on Ca²⁺ regulation and viability in human prostate cancer cells (PC3) is unclear. The present study examined whether nortriptyline altered basal [Ca ²⁺]_i levels in suspended PC3 cells using fura-2 as a Ca²⁺-sensitive fluorescent probe. Nortriptyline (50-500μM) increased [Ca²⁺]_i in a concentration-dependent fashion. The Ca²⁺ signal was partially reduced by removing extracellular Ca²⁺, indicating that Ca²⁺ entry and release both contributed to the [Ca²⁺]_i rise. Nortriptyline induced Mn²⁺ influx, leading to quench of fura-2 fluorescence, suggesting Ca²⁺ influx. This Ca²⁺ influx was inhibited by activation of protein kinase C, but not by inhibition of L-type Ca²⁺ channels. In Ca²⁺-free medium, pretreatment with the endoplasmic reticulum Ca²⁺ pump inhibitor, thapsigargin nearly abolished nortriptyline-induced Ca²⁺ release. Conversely, pretreatment with nortriptyline greatly reduced the inhibitor-induced [Ca²⁺] _i rise, suggesting that nortriptyline released Ca²⁺ from the endoplasmic reticulum. Inhibition of phospholipase C did not change the nortriptyline-induced [Ca²⁺]_i rise. Nortriptyline at a concentration of 10 μM increased viability in a Ca²⁺-independent manner. At 50 μM, nortriptyline killed 45% of cells. Nortriptyline at 10 μM did not induce apoptosis, but at 50 μM induced significant apoptosis measured by propidium iodide staining. Together, in PC3 cells, nortriptyline induced [Ca²⁺]_i rises by causing the phospholipase C-independent Ca²⁺ release from the endoplasmic reticulum and Ca ²⁺ influx via the protein kinase C-sensitive pathway. Nortriptyline also induced both cell proliferation and death in a concentration-dependent manner. Apoptosis was involved in the cell death.