ER stress induces intracellular Ca²⁺ levels after TMZ treatment.

<p>(A) U87 MG cells were treated with 400 µM TMZ or combined with 10 mM 4-PBA or 5 µM BAPTA-AM/2 mM EGTA for the indicated time periods. Then the level of intracellular Ca²⁺ was measured using flow cytometry with Fluo-3 AM staining. U87 MG cells were pretreated with the indicated concentrations of 5 µM BAPTA-AM/2 mM EGTA for 1 h, followed by treatment with 400 µM TMZ for another 72 h to determine percentages of cells undergoing autophagy and apoptosis (B), as well as the cell viability (C) and percent of LDH release (D). (E) Colony formation was measured after TMZ and BAPTA-AM/EGTA co-treatment. Results are presented as the mean ± SD. **<i>p</i><0.01 vs. each respective control. ^##<i>p</i><0.01 vs. each respective TMZ group.