In cell biology, potassium channels are the most common type of ion channel. They form potassium-selective pores that span cell membranes. Potassium channels are found in most cells, and control the electrical excitability of the cell membrane. They shape action potentials and set the resting membrane potential. They regulate cellular processes such as the secretion of hormones and their malfunction can lead to diseases.
Potassium channels open or close in response to the transmembrane voltage, the presence of calcium ions or other signalling molecules. When open, they allow potassium ions to cross the membrane at a rate which is nearly as fast as their diffusion through bulk water. There are over 80 mammalian genes that encode potassium channel subunits. Potassium channels have a tetrameric arrangement. Four subunits are arranged around a central pore. All potassium channel subunits have a distinctive pore-loop structure that lines the top of the pore and is responsible for potassium selectivity.
Potassium channels found in bacteria are amongst the most studied of ion channels, in terms of their molecular structure. Using X-ray crystallography, profound insights have been gained into how potassium ions pass through these channels and why (smaller) sodium ions do not. The 2003 Nobel Prize for Chemistry was awarded to Rod Mackinnon for his pioneering work on this subject.