BK channels (also called Maxi-K or slo1) are potassium ion channels. They are activated by changes in membrane electrical potential and increases in intracellular [Ca2+]. Opening of BK channels results in cell membrane hyperpolarization. BK channels are tetramers of dimer subunits formed by the association of a pore-forming alpha subunit, always derived from the same gene KCNMA1, and a modulatory beta subunit, dervied from one of 4 human genes KCNMB11-4. Intracellular calcium regulates the physical association between the alpha and beta subunits.