Fig. 5.

A. The total Ca²⁺ buffering capacity, κ, calculated from data as Δ[Ca²⁺]_Total/Δ[Ca²⁺]_Free plotted versus Δ[Ca²⁺]_Free. A1. For exogenous dye alone, the solid curve is κ calculated from Eq. 3. Without endogenous buffer, the fit yielded V_E=−0.52 (as already noted) and the resulting curve fell below the data points. Including dye plus one endogenous buffer (A2) yielded V_E=0.33 and a better fit to the data. B1. 1/κ was plotted versus Δ[Ca²⁺]_Free for the same fit in A1. The solid curve was obtained by inverting Eq. 4. B2. κ_endo was calculated as Δ[Ca²⁺]_Total/Δ[Ca²⁺]_Free−κ_dye, with κ_dye from Eq 4. 1/κ_endo was plotted as a function of Δ[Ca²⁺]_Free. The solid curve is 1/κ_endo from Eq. 4 with K_d,E1 and B_T,E1 from Fig. 3B. Note that in A1 and B1 different values for the dye K_d (278 nM vs. 424 nM) altered the concentration scales from those in A2 and B2.