Decreased extracellular**potassium leads to hyperpolarization:**
Lower potassium levels in the extracellular space will cause hyperpolarization of the resting membrane potential. As a result, a greater than normal stimulus is required for depolarization of the membrane in order to initiate an action potential.
The structure of the voltage gated K+ channel is that of six transmembrane helices along the lipid bilayer.
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.
