Ca²⁺-dependent K⁺ (K_Ca) channels are divided according to biophysical properties and gene homology into two main groups. K_Ca 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 BK_Ca or maxiK, encoded by the slo or KCNMA1 gene).