Figure 1.

Ca²⁺ dependence of channel open probability of the three RyR isoforms. Ca²⁺ dependence measured by ryanodine binding to rabbit muscle preparations. (A) Data and fits by Eq. 2 in the absence of extracellular-side Mg²⁺. (B) Best fits in 1 mM Mg²⁺. Data from Murayama and Kurebayashi (2011); fit parameters listed with their Fig. 2. The dashed curve in B represents the best fit to rate constants of Ca²⁺ release from cardiac SR vesicles, measured with stopped-flow mixing by Sánchez et al. (2003) in the absence of Mg²⁺. The equation is

$$k=k_{\max }\frac{{[{\mathrm{Ca}}^{2+}]}^{n_a}{K}_i{}_{}^{n_i}}{K_a{}^{n_a}{K}_i{}^{n_i}+{[{\mathrm{Ca}}^{2+}]}^{n_a}{K}_i{}^{n_i}+{[{\mathrm{Ca}}^{2+}]}^{n_i}{K}_a{}^{n_a}},$$

with parameter values given in their Fig. 5.