Figure 2.

Comparison of the Ca²⁺ uniporter models (lines) to the experimental data (points) on the extramatrix Ca²⁺ and ΔΨ-dependencies of mitochondrial Ca²⁺ uptake measured both in the presence and absence of extramatrix Mg²⁺. Shown are the fittings of three different versions of the kinetic model (Model 1, Model 2, and Model 3) to the kinetic data of (A and B) Crompton et al. (9) in which the initial rates of Ca²⁺ influx in response to variations in extramatrix [Ca²⁺] were measured in energized mitochondria of rat hearts suspended (A) in a medium containing 0 mM Mg²⁺ and 0 mM Pi and (B) in a medium containing 0 and 1 mM Mg²⁺ and 1 mM Pi; (C) Bragadin et al. (11) in which the initial rates of Ca²⁺ influx in response to variations in extramatrix [Ca²⁺] were measured in energized mitochondria of rat livers suspended in a medium containing different levels of Mg²⁺ ([Mg²⁺]_e = 0, 2, and 5 mM) and 2 mM Pi; (D) Vinogradov and Scarpa (14) in which the initial rates of Ca²⁺ influx in response to variations in extramatrix [Ca²⁺] were measured in energized mitochondria of rat livers suspended in a medium containing 2 mM Mg²⁺ and 5 mM Pi; (E) Scarpa and Graziotti (15) in which the initial rates of Ca²⁺ influx in response to variations in extramatrix [Ca²⁺] were measured in energized mitochondria of rat hearts suspended in a medium containing 5 mM Mg²⁺ and 2 mM Pi; and (F) Wingrove et al. (16) in which the initial rates of Ca²⁺ influx as a function of ΔΨ were measured in energized mitochondria of rat livers suspended in a medium containing three different levels of Ca²⁺ ([Ca²⁺]_e = 0.5, 1.0, and 1.5 μM), with 0 mM Mg²⁺ and 0.2 mM Pi present in the medium. The models were fitted to these data sets by setting ΔΨ at 140 mV for the data corresponding to 0 mM Pi (A) and 190 mV for the data corresponding to ≥ 1 mM Pi (B–E). Matrix [Ca²⁺] was fixed at 250 nM and matrix [Mg²⁺] was fixed at 0.4 mM.