Figure 3. Predicted sensitivities (color maps) of mitochondrial Ca²⁺ uptake as functions of extra-matrix [Ca²⁺] and ΔΨ in response to variation in matrix [Ca²⁺] using our present alternate model of mitochondrial Ca²⁺ uniporter and their comparisons to the available experimental data (points).

Simulations and fittings are shown only for Model 1 under Case 1 with the biophysical parameters β _e and β _x as functions of ΔΨ. Plot A shows the model simulations and fittings to the kinetic data of Scarpa and Graziotti [12] in which the initial rates of Ca²⁺ uptake were measured in respiring mitochondria isolated from rat hearts with varying levels of extra-matrix Ca²⁺. Plot B shows the model simulations and fittings to the kinetic data of Vinogradov and Scarpa [13] in which the initial rates of Ca²⁺ uptake were measured in respiring mitochondria isolated from rat livers with varying levels of extra-matrix Ca²⁺. For these analyses, ΔΨ was fixed at 190 mV, corresponding to state 2 respiration. Plot C shows the model simulations and fittings to the kinetic data of Wingrove et al. [16] in which the initial rates of Ca²⁺ uptake were measured as a function of ΔΨ in respiring mitochondria isolated from rat livers with three different levels of extra-matrix Ca²⁺ ([Ca²⁺]_e = 0.5 µM, 1.0 µM, and 1.5 µM). For sensitivity color maps, matrix [Ca²⁺] was varied from 100 nM to 500 nM. The black lines corresponding to the model fittings to the data are based on 250 nM of matrix [Ca²⁺]. The model uses the parameter values estimated based on the present uniporter model (Table 2).