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

Abstract: 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 (≥10 μM) caused a [Ca2+]i rise in a concentration‐dependent manner (EC50=200 μM). 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 μM nortriptyline killed 78% and 97% of cells, respectively; while 10 μM 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.