Calcium-activated potassium channels are potassium channels gated by calcium.^[1]. This family of ion channels is, for the most part, activated by intracellular Ca²⁺ and contains 8 members (KCa1.1, KCa2.1, KCa2.2, KCa2.3, KCa3.1, KCa4.1, KCa4.2, KCa5.1) in the human genome.

Knowing the structure of these channels can provide insight into their function and mechanism of gating. They are made up of two different subunits, alpha and beta. The alpha subunit is a tetramer which forms the pore, the voltage sensor, and the calcium sensing region. This subunit of the channel is made up of seven trans-membrane units, and a large intracellular region. The voltage sensor is made by the S4 transmembrane region, which has several Arginine residues which act to 'sense' the changes in charge and move in a very similar way to other voltage gated potassium channels. As they move in response to the voltage changes they open and close the gate. The linker between the S5 and S6 region serves to form the pore of the channel. Inside of the cell, the main portion to note is the calcium bowl. This bowl is thought to be the site of calcium binding ^[2].

Yellow Sphere was 17β-Estradiol binding site (residues W163, and F166) in the voltage- and Ca²⁺-activated K⁺ (BK) channel β1 subunit.^[3].

Radioligand binding experiments showed that this common His residue (H337N) located in the S5-PHelix loop was crucial to the inhibitory interaction of apamin with the channel ^[8]. Paxilline blocked maxi-K channels at a site distinct from the ChTX binding site located near the external entrance to the pore ^[11].

IKCa1 identified Thr250 in the P-region and Val275 in S6 (red sphere) as being critical for TRAM binding ^[4]. White Sphere was magnesium activation of calcium-activated potassium channel binding site (residues E374, E399 and Q397).^[5]. Blue Sphere was Bisphenol A activates BK channels through effects on α and β1 subunits binding site (residues T169, L172, and L173) ^[6]. The PHU-binding pocket includes A477, L480 and V481 of CaMBD, and F19, I27, L32, M51, I52, V55, I63, F68 and M71 of CaM was binding for 1-EBIO and NS309 ^[7]. BK activation by Cym04 occurs in a splice variant-specific manner; it does not occur in such Slo1 BK channels using an alternative neuronal exon 9, which codes for the linker connecting the transmembrane segment S6 and the cytosolic RCK1 domain—the S6/RCK linker ^[10].

Apamin does not behave as a classical pore blocker but blocks using an allosteric mechanism for KCa2 channel ^[9].