Inhibitory effects of extracellular Mg~(2+) on intracellular Ca~(2+) dynamic changes and thapsigargin-induced apoptosis in human cancer MCF7 cells

摘要

The effect of extracellular Mg~(2+) on both dynamic changes of [Ca~(2+)]_i and apoptosis rate were analysed. The consequences of spatial and temporal dynamic changes of intracellular Ca~(2+) on apoptosis, in thapsigargin- and the calcium-ionophore 4BrA23187-treated MCF7 cells were first determined. Both 4BrA23187 and thapsigargin induced an instant increase of intracellular Ca~(2+) concentrations ([Ca~(2+)]_i) which remained quite elevated (> 150 nM) and lasted for several hours. [Ca~(2+)]_i increases were equivalent in the cytosol and the nucleus. The treatments that induced apoptosis in MCF7 cells were systematically associated with high and sustained [Ca~(2+)]_i (150 nM) for several hours. The initial [Ca~(2+)]_i increase was not determinant in the events triggering apoptosis. Thapsigargin-mediated apoptosis and [Ca~(2+)]_i rise were abrogated when cells were pretreated with the calcium chelator BAPTA. The role of the extracellular Mg~(2+) concentration has been studied in thapsigargin treated cells. High (10 mM) extracellular Mg~(2+), caused an increase in basal [Mg~(2+)]_i from 0.8 ± 0.3 to 1.6 ±0.5 mM. As compared to 1.4 mM extracellular Mg~(2+), 1 μM thapsigargin induces, in 10 mM Mg~(2+) , a reduced percentage from 22 to 11% of fragmented nuclei, a lower sustained [Ca~(2+)]_i and a lower Ca~(2+) influx through the plasma membrane. In conclusion, the cell death induced by thapsigargin was dependent on high and sustained [Ca~(2+)]_i which was inhibited by high extracellular and intracellular Mg~(2+).