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 (> or = 10 microM) caused a Ca2+]i rise in a concentration-dependent manner (EC50 = 200 microM). 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 100 microM nortriptyline killed 78% and 97% of cells, respectively; while 10 microM 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.