Extended Data Fig. 7: Quantitative analysis of Ca²⁺ release sites, assuming looser RyR packing.

Data are presented as in Fig. 4, but with estimates of RyR number based on packing density reported from DNA-PAINT studies¹⁰. We note that this is a scalar adjustment, and thus proportional differences between groups remained similar. (a) Nearest RyR cluster sizes for single-release (blue) and multirelease sparks (orange), compared to the overall distribution of RyR cluster sizes (pink). (b) Mean estimates of RyR configurations underlying Ca²⁺ sparks. Please refer to Extended Data Fig. 9 for evidence that there was no apparent density shift in RyR packing for single- and multirelease sparks. Data are presented as mean ± SEM. Differences between groups were tested with two-tailed linear mixed models with Tukey post hoc correction for multiple comparisons. *** = P < 0.001. P values: cluster size: 4.57x10^-5, local RyR density: 4.3x10^-4, local cluster count: 0.1748. For n values, see Supplementary Table 3, middle column. (c) Mathematical modeling prediction of maximal spark amplitude based on the underlying RyR cluster arrangement, with experimental data superimposed. (d) Estimated number of peak open RyRs for each recorded Ca²⁺ spark. (e) Estimated RyR open probability.