Does the Intracellular Activation Gate Move in Response to Depolarization?
Although channels containing four subunits carrying the W434F mutation do not conduct in the presence of permeant ions, intracellular blockers like tetraethylammonium (TEA) reveal that the intracellular gate still opens and closes in response to changes in membrane voltage. In W434F, intracellular TEA slows the return of OFF gating charge because the blocker binds to the open conformation of the gate and prevents closure, an event that appears to be required for the voltage sensors to return to their resting conformations (Bezanilla et al., 1991; Perozo et al., 1993; Melishchuk and Armstrong, 2001). In effect, the kinetics of the decay of OFF gating current is a sensitive indicator of whether the intracellular gate moves between open and closed conformations even though the channel cannot conduct ions due to structural changes in the external vestibule. To address whether the intracellular activation gate moves in the V478W mutant, we examined the effects of intracellular TEA on the de
