Estimating jSR Ca²⁺ depletion and RyR gating time course by flux reconstructions. (A) The 3-D model of Ca²⁺ reactions, diffusion, and microscope blurring shown in Fig. 2 generates a Ca²⁺ spark record, which is fitted to experimental data by varying a basis function for the jSR permeability time course (Kong et al., 2013). (B) Although not fitted, the model can also calculate the corresponding SR Ca²⁺ depletion signals, which are similar to those recorded experimentally (Brochet et al., 2005). (C) From the calculated release flux (red) and the jSR Ca²⁺ levels, the jSR permeability time course was derived (normalized flux in red and normalized nP_o [number of open channels] in blue). (D) Normalized release flux (red) and permeability (blue) changes from the induction decay model of Cannell et al. (2013). Note the concordance of flux estimates by both models, although the permeability time course is dependent on species-dependent RyR Ca²⁺ sensitivity.