Figure 2.

H₂O₂ initially decreases the thresholds for SOICR. HEK293 cells stably expressing RyR2 were transfected with the luminally expressed FRET-based Ca²⁺ indicator; D1ER. The cells were superfused with KRH containing 1 or 2 mM Ca²⁺ and varying concentrations of H₂O₂ (10–1000 μM). At the end of each experiment cells were perfused with 2 mM tetracaine and 20 mM caffeine to determine the maximum and minimum store capacities, respectively. (A–C) Representative traces from cells exposed to 10, 250, and 1000 μM H₂O₂; dashed lines represent the release (before: F_SOICR and after: F_SOICR^∗ H₂O₂) and termination (before: F_Termi and after: F_Termi^∗ H₂O₂) SOICR thresholds or maximum (Max) and minimum (Min) store levels. (D–G) H₂O₂-mediated changes in the SOICR threshold for release, SOICR termination threshold, magnitude of Ca²⁺ release, and max store level and store size, respectively. Control n = 39, 10 μM n = 24, 25 μM n = 28, 50 μM n = 32, 100 μM n = 36, 250 μM n = 40, 500 μM n = 34, and 1000 μM n = 33. Data shown are mean ± SE. ^∗∗p < 0.01; ^∗∗∗∗p < 0.0001; compared to control (no H₂O₂).