Trapping the sensor.

Voltage-gated ion channels open in response to a change in membrane potential. The "sensor," or the channel's molecular entity responsible for the detection of voltage change, is formed by a transmembrane element, rich with basic residues, called the "voltage sensor" or the "S4 domain." The movement of the S4 drives a global conformational change leading to the opening of the permeation pathway and ion conduction. In this issue of Neuron, Schönherr and colleagues show that physical constrains of the "gating canal," or the crevice through which the S4 moves, determines whether voltage-gated potassium channels open quickly or slowly.