Figure 4. Na⁺_c dependence of Ca²⁺ efflux via forward mode of NCX_mito.

A, time course of Ca²⁺_mito decrease. The myocytes were preloaded with 300 nm Ca²⁺_c and Ca²⁺ efflux via forward mode of NCX_mito was induced by applying the bath solution with no Ca²⁺ and various Na⁺_c as denoted on the right of graph. CGP-37157 (30 μm) was added to the solution with 6 mm Na⁺ (•). The Rhod-2 fluorescence was normalized to that before changing the solution. B, Na⁺_c dependence of initial decay velocity of Ca²⁺ efflux. The initial decay velocity of Ca²⁺ efflux (2.1 ± 0.4, 3.1 ± 1.3, 13.3 ± 7.1, 39.7 ± 5.9, 76.2 ± 13.9 and 56.5 ± 13.9% min⁻¹ in the presence of 0, 0.3, 0.6, 1, 6 and 20 mm Na⁺_c, respectively) was fitted by a Hill equation: 2.2 + 64.2/(1 + (0.9/Na⁺_c)^3.8). n = 4–7.