Potassium channels (picture: potassium channels in the bacterium Streptomyces lividans) are channels allowing for fast transport of potassium ions through cell membranes.
Ion channels are found in the cell membrane and are responsible for ion flux, which plays an important role in many biological processes, for example in nerve activity or muscle contraction.
The channels are formed by transmembrane proteins.
Ion channels are highly selective. They contain two parts, which are essential to their role: the selectivity filter and the gate.
The gate determines under which conditions the channel, which is closed and thus impermeable in the resting state, is opened.
The selectivity filter determines which ions are allowed to pass through the channel.