Calcium-activated potassium channel

Calcium-activated potassium channels are divided into BK channels, IK channels, and SK channels based on their conductance (big, intermediate, and small conductance).

This family of ion channels is, for the most part, activated by intracellular Ca2+ and contains 8 members. It should be noted, however, that some of these channels (the KCa4 and KCa5 channels) are responsive instead to intracellular Na+ and Cl-. Furthermore, the KCa1 family is both Ca2+ and voltage activated, further complicating the description of this family. The KCa channel α subunits have six transmembrane segments similar to the KVs, except KCa1, in which the N-terminus makes a seventh pass across the membrane to end up outside the cell. The α subunits make homo- and hetero-tetrameric complexes.

Homology classification
Below is a list of the 8 known calcium-activated potassium channel grouped according to sequence homology of transmembrane hydrophobic cores:

BK channel

 * Kca1.x : Kca1.1

SK channel

 * Kca2.x : Kca2.1, Kca2.2 , Kca2.3
 * Kca3.x: Kca3.1
 * Kca4.x: Kca4.1, Kca4.2

IK channel

 * Kca5.x: Kca5.1