Ca2+ dependent K+ (KCa) channels are divided according to biophysical properties and gene homology into two main groups. KCa were first divided according to their single channel conductance, which represents the speed by which the K+ passes via the open channel. The first group consists of small and intermediate conductance channels (SK and IK respectively, the KCNN gene family). The second group is comprised of large/big conductance channels (called BKCa or maxiK, encoded by the slo or KCNMA1 gene).