Figure 1. Voltage-dependent modification of Na_v1.4 by MTS reagent.

The chemical modification reactions for the two states (inside at negative and outside at positive voltages) are designated, ρ_mod- and ρ_mod+ and lead to two corresponding modified cysteine states, Cys_V- ^Mod and Cys_V+ ^Mod. The rates of movements of the voltage sensor are denoted by voltage dependent rate constants α(V) and β(V) for unmodified channels and α’(V) and β’(V) for modified channels.