of a selective pharmacological blocker for voltage gated K+ channels. The lack of repolarization means that neuron stays at a high voltage, which slows sodium channel deinactivation to a point where there is not enough inwards Na+ current to depolarize and sustain firing. Voltage gated K+ mechanisms The structure of the voltage gated K+ channel is that of six transmembrane helices along the lipid bilayer. The selectivity of this channel to voltage is mediated by four of these transmembrane domains (S1–S4) – the voltage sensing domain. The other two domains (S5, S6) form the pore by which ions traverse. Activation and deactivation of the voltage gated K+ channel is triggered by conformational changes in the voltage sensing domain. Specifically, the S4 domain moves such that it activates and deactivates the pore. During activation, there is outward S4 motion, causing tighter VSD-pore linkage. Deactivation is characterized by inward S4 motion. The switch from depolarization into repolarization is dependent on the kinetic mechanisms of both voltage gated K+ and Na+ channels. Although both voltage gated Na+ and K+ channels activate at roughly the same voltage (−50 mV), Na+ channels have faster kinetics and activate/deinactivate much more quickly. Repolarization occurs as the influx of Na+ decreases (channels deinactivate) and the efflux of K+ ions increases as its channels open. The decreased conductance of sodium ions and increased conductance of potassium ions cause the cell's membrane potential to very quickly return to, and past the resting membrane potential, which causes the hyperpolarization due to the potassium channels closing slowly, allowing more potassium to flow through after the resting membrane potential has been reached. Type of K+ channels in repolarization Following the action potential, characteristically generated by the influx of Na+ through voltage gated Na+ channels, there is a period of repolarization in which the Na+ channels are inactivated while K+ channels are activated. Further study of K+ channels shows that there are four types which influence the repolarization of the cell membrane to re-establish the resting potential. The four types are Kv1, Kv2, Kv3 and Kv4. The Kv1 channel primarily influences the repolarization of the axon. The Kv2 channel is characteristically activated slower. The Kv4 channels are characteristically activated rapidly. When Kv2 and Kv4 channels are blocked, the action potential predictably widens. The Kv3 channels open at a more positive membrane potential and deactivate 10 times faster than the other Kv channels. These properties