Fig 4. SR-Ca²⁺ dependence of SRF distribution parameters.

A–The Dynamic Fit SRF parameters: summary data (points) and the fit from the relevant functions (lines) for the three Ca²⁺ handling conditions (purple–control; blue–CRU-CRU coupling enhancement; orange–SERCA upregulation and NCX downregulation model) against SR-Ca²⁺ for: i) probability of whole-cell SCRE; ii) initiation time corresponding to the separation point, t_i; iii) the normalised cumulative frequency at this point, CF_ti,Sep = F(_ti)|_{ti = ti,Sep}; iv) the k parameter for F₁(t_i) and (v) for F₂(t_i); (vi) the median duration, MD. B–The General Dynamic SRF parameters: i) Illustration of the curve for probability of SCRE and its relation to the user defined parameters (CaSR_thresdhold, CaSR_{P_range}) and derived parameters (CaSR_min). ii) Illustration of the function form describing t_i,Sep and median duration (MD) (purple line) and its relation to CaSR_min, CaSR_max, t_i,Sep^min, t_i,Sep^max, MD^min, MD^max, and how the range of the distributions varies with SR-Ca²⁺ (shaded regions) at two different non-linearity factors (H_width = 0.75, blue; = 2.5, orange).