Potassium channel activated by both membrane depolarization or increase in cytosolic Ca(2+) that mediates export of K(+). It is also activated by the concentration of cytosolic Mg(2+). Its activation dampens the excitatory events that elevate the cytosolic Ca(2+) concentration and/or depolarize the cell membrane. It therefore contributes to repolarization of the membrane potential. Plays a key role in controlling excitability in a number of systems, such as regulation of the contraction of smooth muscle, the tuning of hair cells in the cochlea, regulation of transmitter release, and innate immunity. In smooth muscles, its activation by high level of Ca(2+), caused by ryanodine receptors in the sarcoplasmic reticulum, regulates the membrane potential. In cochlea cells, its number and kinetic properties partly determine the characteristic frequency of each hair cell and thereby helps to establish a tonotopic map. Highly sensitive to both iberiotoxin (IbTx) and charybdotoxin (CTX) (By similarity). Ethanol and carbon monoxide-bound heme increase channel activation. Heme inhibits channel activation (By similarity). Homotetramer; which constitutes the calcium-activated potassium channel. Additional isoforms seem to exist. Expressed in both the somites and neural tube of 1 day embryos. Within the nervous system, it is restricted to dorsal parts, and expressed centrally in regions dedicated to processing of sensory information. Six hours later, it is expressed segmentally within the somites. At this time, it is expressed in a primary sensory organ, the trigeminal ganglion. By 2 days, it is also expressed in other primary sensory organs, such as the otic vesicle, and the eye. Within the retina, it is expressed to an internal layer. In the developing otic vesicle, it is abundantly expressed near the apical surface. Isoform 3 is neural-specific, and is only expressed during late stages of neuronal differentiation. Expressed during embryogenesis before differentiation of excitable tissues. The S0 segment is essential for the modulation by the accessory beta subunits. The S4 segment, which is characterized by a series of positively charged amino acids at every third position, is part of the voltage-sensor. The pore-forming domain (also referred as P region) is imbedded into the membrane, and forms the selectivity filter of the pore. It contains the signature sequence of potassium channels that displays selectivity to potassium (By similarity). The RCK N-terminal domain mediates the homotetramerization, thereby promoting the assembly of monomers into functional potassium channel. It includes binding sites for Ca(2+) and Mg(2+) (By similarity). The calcium bowl constitutes one of the Ca(2+) sensors and probably acts as a Ca(2+)-binding site. There are however other Ca(2+) sensors regions required for activation of the channel (By similarity). The heme-binding motif mediates inhibition of channel activation by heme. Carbon monoxide-bound heme leads to increased channel activation (By similarity). The protein was initially thought to contain two functionally distinct parts: The core channel (from the N-terminus to the S9 segment) that mediates the channel activity, and the cytoplasmic tail (from the S9 segment to the C-terminus) that mediates the calcium sensing. The situation is however more complex, since the core channel contains binding sites for Ca(2+) and Mg(2+). Belongs to the potassium channel family. Calcium-activated (TC 1.A.1.3) subfamily. KCa1.1/KCNMA1 sub-subfamily. It is uncertain whether Met-1 is the initiator or if the sequence starts further upstream.