Fig. 1

Hypothetical mechanisms for a mobile charged intramembrane voltage sensor. a Voltage-dependent intramembrane charge movement could be generated by positive charges moving outward during depolarization, negative charges moving inward, or dipoles rotating. In each, the charge would return to its starting distribution on membrane repolarization, so the charge moved outward during membrane depolarization must equal the charge moving back on repolarization. b Cartoon illustration of current concept of intramembrane voltage sensors as positively charged amino acid residues on transmembrane alpha helices. As in a, the charge moved outward during depolarization (here on an alpha helix) will equal the charge returning on repolarization