Maprotiline-induced Ca²⁺ fluxes and apoptosis in human osteosarcoma cells

The effect of maprotiline on cytosolic free Ca²⁺ concentrations ([Ca²⁺]_i) and cell viability was explored in human osteosarcoma cells (MG63), using the fluorescent dyes fura-2 and WST-1, respectively. Maprotiline at concentrations of ≥20 μM increased [Ca ²⁺]_i in a concentration-dependent manner. The Ca2+ signal was reduced partly by removing extracellular Ca²⁺. The maprotiline-induced Ca²⁺ influx was sensitive to inhibition by aristolochic acid (a phospholipase A₂ inhibitor). In Ca ²⁺-free medium, after treatment with 1 μM thapsigargin (an endoplasmic reticulum Ca²⁺ pump inhibitor), 200 μM maprotiline failed to induce a [Ca²⁺]_i rise. At concentrations of 50-100 μM maprotiline killed cells in a concentration-dependent manner. The cytotoxic effect of 60 μM maprotiline was slightly enhanced by prechelating cytosolic Ca²⁺ with 1,2-bis(2aminophenoxy)ethane-N,N,N′, N′-tetraacetic acid (BAPTA). Propidium iodide staining data suggested that maprotiline induced apoptosis between concentrations of 60-70 mμM, which was enhanced by BAPTA. Collectively, in MG63 cells, maprotiline induced [Ca ²⁺]_i rises by causing Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ influx from phospholipase A ₂-regulated Ca²⁺ channels. Furthermore, maprotiline caused apoptosis that was regulated by Ca²⁺.