Figure 7.

Mutant cycle analysis of mexiletine and pHM binding to the wild-type hNav1.4 channel and its mutants Y1593C and F1586C. Mutant cycle analysis for tonic block considers IC₅₀ values calculated at 0.1 Hz stimulation frequency (A), while IC₅₀ calculated at 10 Hz stimulation frequency allowed mutant cycle analysis for use-dependent block (B). The Xi and Yi values represent the changes in affinity with each mutation, calculated as the ratio of IC₅₀ values. The coupling constant Ω is calculated as the X1 to X2 ratio and the coupling energy ΔG is calculated as RT·lnΩ, where R is the perfect gas constant (8.314 J K mol⁻¹) and T the temperature expressed in Kelvin (295.15 K = 22°C). The calculated ΔG shown in red was converted to kilocalorie per mole.