Effect of Nortriptyline on Intracellular Ca2+ Handling and Proliferation in Human Osteosarcoma Cells.

The effect of the antidepressant nortriptyline, on bone cells is unknown. In human osteosarcoma MG63 cells, the effect of nortriptyline on intracellular Ca²⁺ concentration ([Ca²⁺]_i) and proliferation was measured by using fura-2 and tetrazolium, respectively. Nortriptyline (≥10μM) caused a[Ca²⁺]_i rise in a concentration-dependent manner (EC₅₀=200μM). Nortriptyline-induced[Ca²⁺]_i rise was prevented by 60% by removal of extracellular Ca²⁺ but was not altered by voltage-gated Ca²⁺ channel blockers. In Ca²⁺-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca²⁺-ATPase, caused a monophasic[Ca²⁺]_i rise, after which the increasing effect of nortriptyline on[Ca²⁺]_i was abolished; also, pretreatment with nortriptyline abolished thapsigargin-induced[Ca²⁺]_i increase. U73122, an inhibitor of phospholipase C, did not affect nortriptyline-induced[Ca²⁺]_i rise; however, activation of protein kinase C decrease nortriptyline-induced[Ca²⁺]_i rise by 32%. Overnight incubation with 50 and 100μM nortriptyline killed 78% and 97% of cells, respectively; while 10μM nortriptyline had no effect. These data suggest that nortriptyline rapidly increases[Ca²⁺]_i in human osteosarcoma cells by stimulating both extracellular Ca²⁺ influx and intracellular Ca²⁺ release, and is cytotoxic at high concentrations. [ABSTRACT FROM AUTHOR]