Figure 8.

Model predictions. (A) Comparison of experimental data and model. Symbols represent mean (± SEM) Ca_T data with (filled circles) and without (open circles) tetracaine. The curves are the best fits of the model to the data points. For the tetracaine case (blue line), the model was fitted by adjusting the values of the t-system Ca²⁺ leak and $K_{\mathrm{D}}^{\mathrm{P}\mathrm{M}\mathrm{C}\mathrm{A}}.$ For the non-tetracaine case (red line), $K_{\mathrm{D}}^{\mathrm{P}\mathrm{M}\mathrm{C}\mathrm{A}}$ was assumed to be the same as in the presence of tetracaine, and the parameters adjusted to obtain the best fit were the rate constants for the t-system leak and RYR leak. The parameter values are given in Table 5. (B) Model-derived time courses of Ca_JS in the presence (+Tet, blue line) and absence (−Tet, red line) of a leak of Ca²⁺ through the RYRs. When there is no RYR Ca²⁺ leak, Ca_JS is maintained by the equilibrium with EGTA and diffusion of Ca²⁺ from the myoplasm. In the presence of a RYR Ca²⁺ leak into the JS (red line), sufficient Ca²⁺ enters the JS to increase the unbound [Ca²⁺]. (C) Model-derived time courses of [Ca²⁺] in the SR and t-system in the presence of RYR Ca²⁺ leak. Most Ca²⁺ entering the SR binds to SR Ca²⁺ buffers (Ca_B, right-hand y scale).