Iso does not modify the latency of the first spontaneous Ca²⁺ release in S2030A^+/+ myocytes. (A) Line-scan images were recorded in the end of a train of electrical stimulations at 1 Hz for 30 s. Each cell was recorded in control and after 3 min of 100 nmol/liter Iso treatment. The figure also shows line profiles of the triggered Ca²⁺ transients and the spontaneous Ca²⁺ releases (ΔF/F₀; black traces for the control and red for Iso). The latency was calculated considering the last electrical stimulus and the first spontaneous Ca²⁺ release (arrows). (B) SCaW latency (17.72 ± 3.42 s vs. 8.08 ± 1.16 s), respectively, for control and after Iso stimulation for WT (18.04 ± 1.95 s for control vs. 14.27 ± 2.51 s for Iso in S2030A^+/+). Latency values were not paired, because not all cells displayed SCaW. (C) Occurrence of spontaneous release (percentage of cells that show at least one Ca²⁺ wave; N = 4, n = 16 for WT; N = 4, n = 15 for S2030A^+/+). (D) Comparison of wave speed (WT: N = 4, n = 11; 78.42 ± 5.05 µm/s [control] vs. 99.31 ± 4.03 µm/s [Iso]); S2030A^+/+: N = 4, n = 15; 83.49 ± 5.56 µm/s [control] vs. 85.40 ± 4.64 µm/s [Iso]). In all experiments shown, the SR Ca²⁺ load was not matched experimentally between control and Iso. *, P < 0.05 versus control; †, P < 0.05 versus WT. The whiskers cover the range from 10% to 90%.