Domain-specific charge neutralizations. (A) Sequence alignments of the S4 voltage-sensing segments from each domain in Nav1.4. Mutations are marked in bold. (B) A representative family of ionic current traces for wild-type and mutant channels in response to 30-ms depolarizing pulses from −110 to 65 mV (10-mV steps), preceded by a 20-ms prepulse to −120 mV from a holding potential of −80 mV. (C) Normalized peak G-V relationship for wild-type and mutant channels. Solid lines are single Boltzmann fits to the mean for each construct (wild type: V_1/2 = −23.8 mV and z = 5.8 e⁻; DI-CN: V_1/2 = −36.5 mV and z = 3.8 e⁻; DII-CN: V_1/2 = −25.1 mV and z = 3.3 e⁻; DIII-CN: V_1/2 = −26.4 mV and z = 3.9 e⁻; DIV-CN: V_1/2 = −23.1 mV and z = 3.8 e⁻).