The depletion of ER calcium stores activates two distinct populations of store‐operated calcium channels in SK‐MG‐1 human glioblastoma cell line

Despite intensive research to discover successful therapies for brain tumors, glioblastoma multiforme (GBM), a grade IV glioma, still has an average survival rate of less than 12 months. In non‐excitable cells including astrocytes and gliomas, store‐operated calcium channels (SOCC) are the major Ca 2+ entry pathway. Recently, we have shown that SOCC activity is much larger in human GBM cells and cell lines as compared to normal human astrocytes. In this study, we have characterized SOCC channels in SK‐MG‐1 cells using several SOCC blockers. Using fluorescence spectroscopy we measured intracellular calcium concentration, and Ca 2+ , Ba 2+ , and Sr 2+ entry with Fura‐2. In SK‐MG‐1 glioma cells, thapsigargin (TG), a sarco/endoplasmic reticulum Ca 2+ ATPase inhibitor, increased the Fura‐2 ratio i.e., [Ca 2+ ] I by 1.08 ± 0.3 AU in nominally calcium‐free buffer. This increase was inhibited by SKF 96365 by 20%; Ni 2+ and MRS 1845 had no effect. When 1 mM extracellular calcium was added back after the [Ca 2+ ] I had returned to baseline, the Fura‐2 ratio increased again by 4.83 ± 0.14 AU at a rate of 0.15 ± 0.05 AU/s, consistent with opening of SOCC. This elevation was partially blocked by 2‐APB, SKF 96365, and Ni 2+ , but not by MRS 1845. This TG sensitive channel was also permeable to Sr 2+ . TG increased Ba 2+ entry in SK‐MG‐1 cells by ~10 fold. This Ba 2+ entry pathway was insensitive to 2‐APB, but completely inhibited by Gd 3+ , and La 3+ . These data suggest that ER‐depletion activates at least two types of SOCC channels in SK‐MG‐1 cells. This study was supported by NIH Grant CA101952.