Figure 5.

Ca²⁺ sensitivity analyses in isolated adult cardiomyocytes. (A) Representative Ca²⁺ transient recordings of isolated adult isoproterenol (Iso)- and Iso + NO₂-OA treated cardiomyocytes upon increasing extracellular Ca²⁺ concentrations (0.25 mM–2 mM) stimulated at 1 Hz for 30 s following a non-stimulated period of 20 s in which arrhythmic Ca²⁺ events were recorded (asterisks). (B) Relative Ca²⁺ transient peak height in control- versus Iso- and Iso + NO₂-OA treated cells upon different Ca²⁺ concentrations (Iso vs. Iso + NO₂-OA [∆Fura-2]; 0.25 mM Ca²⁺: 0.71 ± 0.28 vs. 0.6 ± 0.23; 0.5 mM Ca²⁺: 0.73 ± 0.19 vs. 0.71 ± 0.0.28; 1 mM Ca²⁺: 1.01 ± 0.16 vs. 1.05 ± 0.16; 2 mM Ca²⁺: 1.24 ± 0.14 vs. 1.08 ± 0.23). (C) Relative diastolic Ca²⁺ levels measured between the 1 Hz pacing periods (Iso vs. Iso + NO₂-OA [∆Fura-2]; 0.25 mM Ca²⁺: 1.32 ± 0.16 vs. 1.38 ± 0.13; 0.5 mM Ca²⁺: 1.35 ± 0.16 vs. 1.40 ± 0.11; 1 mM Ca²⁺: 1.39 ± 0.16 vs. 1.42 ± 0.11; 2 mM Ca²⁺: 1.45 ± 0.18 vs. 1.45 ± 0.12). (D) Mean number of arrhythmic Ca²⁺ release events within the non-stimulated time period (asterisks, Iso vs. Iso + NO₂-OA [mean number]; 0.25 mM Ca²⁺: 0.5 ± 1.07 vs. 0.0 ± 0.0; 0.5 mM Ca²⁺: 0.22 ± 0.67 vs. 0.0 ± 0.0; 1 mM Ca²⁺: 1.56 ± 4.3 vs. 0.0 ± 0.0; 2 mM Ca²⁺: 2.44 ± 4.82 vs. 0.0 ± 0.0). (B–D) n(cells out of 3 animals) = 9/5 for each concentration. Graphs show Mean ± SEM. Brackets indicate Mean ± SD. * P < 0.05.