| Voltage-gated sodium channels are transmembrane proteins found in excitable tissues that are critical for biological signaling. Cysteine mutagenesis and metal bridging was used to probe for interactions between the positive S4 transmembrane segment residues and surrounding negative residueson S1-S3 in the first domain of human voltage-gated sodium channel (hNaV1.4). Double cysteine mutations (S4 residue and putativecountercharge) were constructed to probe for interaction during activation. Additionally, the DI double mutations were tested for effects on steady-state fast inactivation, a function not generally associated with domain I. All voltage sensor residues had strong interactions during activation with an S2glutamate (E171)in the gating charge transfer centerand displayed weaker interactions with anextracellularS2glutamate (E161) and with anS3 aspartate(D197) in the gating charge transfer center. In addition to activation interactions, DI interactions also produced inactivation effects.Key Words: voltage-gated sodium channel, SCN4A, hNaV1.4, cysteine mutagenesis, G/V, SSFI, domain I, cadmium |