A Potassium ion channel is a transmembrane protein that allows for the selective movement of potassium ions (K+).
There are 13 classes of potassium channels.
At a resting potential in neurons, potassium channels are leaky - they are open, but potassium ions do not flow, through because of the electrochemical equlibrium. At threshold potential, potassium channels close, but at the center of an action potential, at the top of the overshoot, voltage-gated potassium ion channels open, and allow potassium ions to enter and bring the neuron to threshold. Then, a second type of potassium channels open, hyperpolarizing the neuron beyond the threshold - undershoot. Eventually, the neuron returns to resting potential.
Mechanically-gated potassium channels also exist. Mechanically-gated potassium channels are present in the pseudocilia of hair cells in the cochlea. The deflection of the basalar membrane forces the hair cells to shift, and depending on the new positions of the hair cells, potassium channels can open from the mechanical displacement, and repolarize the hair cell.