Ion Channel Voltage Sensors: Structure, Function, and Pathophysiology

Voltage-gated ion channels generate electrical signals in species from bacteria to man. Their voltage-sensing modules are responsible for initiation of action potentials and graded membrane potential changes in response to synaptic input and other physiological stimuli. Extensive structure-function studies, structure determination, and molecular modeling are now converging on a sliding-helix mechanism for electromechanical coupling in which outward movement of gating charges in the S4 transmembrane segments catalyzed by sequential formation of ion pairs pulls the S4-S5 linker, bends the S6 segment, and opens the pore. Impairment of voltage-sensor function by mutations in Na+ channels contributes to several ion channelopathies, and gating pore current conducted by mutant voltage sensors in NaV1.4 channels is the primary pathophysiological mechanism in hypokalemic periodic paralysis. The emerging structural model for voltage sensor function opens the way to development of a new generation of ion-channel drugs that act on voltage sensors rather than blocking the pore.