Figure 6.

Characteristics of Ca²⁺ buffers. (A) Ca²⁺–EGTA dissociation curve. Variation of concentrations of bound Ca²⁺ (Ca·EGTA; black line, left y axis) and unbound or free Ca²⁺ (Ca; green line, right y axis) with total Ca²⁺. Note the 10⁶-fold difference in the scales of the y axes. (B) Equilibrium binding curve for SR Ca²⁺ buffers (including Csq). Solid red curve, relationship for the model used in the current study determined from equilibrium solution of Eq. 10 with total buffer Ca²⁺ binding site concentration = 70 mM, $K_{\mathrm{D}}^{\mathrm{B}}$ = 450 μM, and n = 3.5. Black curve, the empirical relationship determined by Manno et al. (2013; from their Fig. 7 A). (C) SR–Ca²⁺ buffer dissociation curve showing variations in bound Ca²⁺ (Ca·B; magenta line, left x axis) and unbound, or free, Ca²⁺ (green line, right x axis) with total SR Ca²⁺ content.