Fig. 6: Ratiometric Ca²⁺ imaging of RBL-1 cells with and without extracellular Ca²⁺ with corresponding TEM micrographs.

a Fura-2 based imaging of cytosolic Ca²⁺ concentration of RBL-1 cells in presence of 2 mM Ca²⁺. Cells were treated with 2 µM TG at the indicated time point (arrow) or left untreated, Ctrl (Ctrl, blue) and Thapsigargin (TG, red). Quantification of (b) basal Ca²⁺ (c) max Ca²⁺ influx and (d) area under the curve (AUC) of traces shown in (a), n = 51–61 cells. e Fura-2 based imaging of cytosolic Ca²⁺ concentration of RBL-1 cells in absence of Ca2+. Cells were treated with 2 µM TG at the indicated time point (arrow) or left untreated, Ctrl (Ctrl, black) and thapsigargin (TG, red). Quantification of (f) basal Ca²⁺ (g) max Ca²⁺ influx and (h) area under the curve (AUC) of traces shown in A, n = 48–54 cells. (i-k) Different cells, intracellular areas and magnifications of 2 µM TG-treated RBL-1 cells (60 min), without extracellular Ca²⁺ as a direct ultrastructural comparison to the Ca²⁺ imaging experiments. Cells show typical autotic hallmarks such as ballooning of the perinuclear space (ps) and vacuolization (v). In addition to that, cells show bloating of the ER (er) and regular mitochondrial (m) morphology.