Figure 3.

Comparison of the 3Na⁺-1Ca²⁺ antiporter models (lines) to the experimental data (points) of Paucek and Jaburek (7) on the kinetics of Na⁺-Ca²⁺ fluxes via the antiporter with fixed external pH. Shown are the best fits of three different kinetic models (Model 1, Model 2, and Model 3) under two different model assumptions (Case 1, (A, C); Case 2, (B, D)) to the kinetic data of Paucek and Jaburek, in which the initial rates of Ca²⁺ influx (Na⁺ efflux) with variations in external [Ca²⁺] ([Na⁺]_x = 25 mM, [Na⁺]_e = 0 mM, [Ca²⁺]_x = 0 μM, pH_x = 7.3, and pH_e = 7.3) (A, B), and the initial rates of Na⁺ influx (Ca²⁺ efflux) with variations in external [Na⁺] ([Na⁺]_x = 0 mM, [Ca²⁺]_x = 10 μM, [Ca²⁺]_e = 0 μM, pH_x = 7.3, and pH_e = 7.3) (C, D) were measured in proteoliposomes reconstituted with purified Na⁺-Ca²⁺ antiporters of beef heart mitochondria. The models were fitted to the data with ΔΨ = 0 mV, in consistence with the experimental protocol. The scaling factor used to scale the model simulated Na⁺ fluxes to match the data on Na⁺ fluxes is 2/n = 2/3 (n = 3 is the stoichiometry in nNa⁺-1Ca²⁺ exchange).