S2030 site ablation limits the Iso-dependent increase in CaSpF. (A) Confocal line-scan images showing Ca²⁺ sparks in intact cells in control and after 3 min of 100 nmol/liter Iso treatment for WT (N = 4, n = 12), S2030A^+/+ (N = 4, n = 13), and S2808A^+/+ (N = 3, n = 10) myocytes. (B) The basal CaSpF (number of sparks per 100 µm/s) was similar among the animal groups; after application of Iso, the CaSpF in S2030A^+/+ myocytes was significantly lower compared with WT and S2808A^+/+ cells. (C) SR Ca²⁺ content was not significantly different between the mouse models. Please note that unlike in the patch-clamp experiments, the SR Ca²⁺ load here was not matched between control and Iso. *, P < 0.05 versus control; †, P < 0.05 versus WT. The whiskers cover the range from 10% to 90%.