Calcium-activated potassium channel

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Calcium-activated potassium channels are potassium channels gated by calcium,^[1] or that are structurally or phylogenetically related to calcium gated channels. They were first discovered in 1958 by Gardos who saw that calcium levels inside of a cell could affect the permeability of potassium through that cell membrane. Then in 1970, Meech was the first to observe that intracellular calcium could trigger potassium currents. In humans they are divided into three subtypes: large conductance or BK channels, which have very high conductance which range from 100 to 300 pS, intermediate conductance or IK channels, with intermediate conductance ranging from 25 to 100 pS, and small conductance or SK channels with small conductances from 2-25 pS.^[2]

This family of ion channels is, for the most part, activated by intracellular Ca²⁺ and contains 8 members in the human genome. However, some of these channels (the K_Ca4 and K_Ca5 channels) are responsive instead to other intracellular ligands, such as Na⁺, Cl⁻, and pH. Furthermore, multiple members of family are both ligand and voltage activated, further complicating the description of this family. The K_Ca channel α subunits have six or seven transmembrane segments, similar to the K_V channels but occasionally with an additional N-terminal transmembrane helix. The α subunits make homo- and hetero-tetrameric complexes. The calcium binding domain may be contained in the α subunit sequence, as in K_Ca1, or may be through an additional calcium binding protein such as calmodulin.