Fig. 3. Isolated pancreatic islets and β-cells have an atypical ER leak that is independent of SERCA activity. (A) Curves reflect normalized [Ca²⁺]_ER ratio signals over time measured with the genetically encoded Ca²⁺ probe D1ER in HeLa (blue curve), EA.hy926 (black curve), INS-1 (green curve) and MIN-6 (red curve) cells perfused with experimental buffer containing 2 mM Ca²⁺ for two min before switching to 0 mM Ca²⁺ and EGTA-containing buffer (n ≥ 6). (B) Representative curves for β-cells (depicted INS-1) reflect [Ca²⁺]_ER ratio signals over time in the presence (2 mM Ca²⁺; black curve) or absence (0 mM Ca²⁺; red curve) of Ca²⁺ measured with D1ER. The ER Ca²⁺ store was depleted using carbachol (100 µM) and BHQ (15 µM) in Ca²⁺-free EGTA-buffered solution prior to addition of 2 mM external Ca²⁺ (n ≥ 6).