Description: potassium large conductance calcium-activated channel, subfamily M, alpha member 1
Gene: Kcnma1     Synonyms: Slo1, Slo, BKCa, mSlo, MaxiK, mSlo1, kcnma1

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KCNMA1 (also known as SLO; BKTM; SLO1; MaxiK; SAKCA; mSLO1; KCa1.1; MGC71881; SLO-ALPHA; bA205K10.1; DKFZp686K1437) encodes Slo1, a potassium large conductance calcium-activated channel, subfamily M, alpha member 1. MaxiK channels are fundamental to the control of smooth muscle tone and neuronal excitability. MaxiK channels can be formed by 2 subunits: the pore-forming alpha subunit, which is the product of this gene, and the modulatory beta subunit. Intracellular calcium regulates the physical association between the alpha and beta subunits. Alternatively spliced transcript variants encoding different isoforms have been identified.



RGD ID Chromosome Position Species
620715 15 575136-950275 Rat
731982 14 24117983-24823427 Mouse
731981 10 78629359-79397577 Human

Kcnma1 : potassium large conductance calcium-activated channel, subfamily M, alpha member 1



Acc No Sequence Length Source
NM_031828 n/A n/A NCBI
NM_010610 n/A n/A NCBI
NM_002247 n/A n/A NCBI
NM_001161352 n/A n/A NCBI
NM_001161353 n/A n/A NCBI
NM_001014797 n/A n/A NCBI



Accession Name Definition Evidence
GO:0016020 membrane Double layer of lipid molecules that encloses all cells, and, in eukaryotes, many organelles; may be a single or double lipid bilayer; also includes associated proteins. IEA
GO:0016324 apical plasma membrane The region of the plasma membrane located at the apical end of the cell. IEA
GO:0016021 integral to membrane Penetrating at least one phospholipid bilayer of a membrane. May also refer to the state of being buried in the bilayer with no exposure outside the bilayer. When used to describe a protein, indicates that all or part of the peptide sequence is embedded in the membrane. IEA
GO:0005901 caveola A membrane raft that forms small pit, depression, or invagination that communicates with the outside of a cell and extends inward, indenting the cytoplasm and the cell membrane. Examples include any of the minute pits or incuppings of the cell membrane formed during pinocytosis. Such caveolae may be pinched off to form free vesicles within the cytoplasm. IEA
GO:0008076 voltage-gated potassium channel complex A protein complex that forms a transmembrane channel through which potassium ions may cross a cell membrane in response to changes in membrane potential. IEA
GO:0005886 plasma membrane The membrane surrounding a cell that separates the cell from its external environment. It consists of a phospholipid bilayer and associated proteins. IEA
GO:0005783 endoplasmic reticulum The irregular network of unit membranes, visible only by electron microscopy, that occurs in the cytoplasm of many eukaryotic cells. The membranes form a complex meshwork of tubular channels, which are often expanded into slitlike cavities called cisternae. The ER takes two forms, rough (or granular), with ribosomes adhering to the outer surface, and smooth (with no ribosomes attached). IEA
GO:0045211 postsynaptic membrane A specialized area of membrane facing the presynaptic membrane on the tip of the nerve ending and separated from it by a minute cleft (the synaptic cleft). Neurotransmitters across the synaptic cleft and transmit the signal to the postsynaptic membrane. IEA
GO:0009897 external side of plasma membrane The side of the plasma membrane that is opposite to the side that faces the cytoplasm. IEA
GO:0044444 cytoplasmic part Any constituent part of the cytoplasm, all of the contents of a cell excluding the plasma membrane and nucleus, but including other subcellular structures. IEA
GO:0043195 terminal button Terminal inflated portion of the axon, containing the specialized apparatus necessary to release neurotransmitters. The axon terminus is considered to be the whole region of thickening and the terminal button is a specialized region of it. IEA

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Carbon monoxide (CO) is a potent activator of slo1 when heterologously expressed in human embryonic kidney 293 (HEK 293) cells (Jaggar [1123], Williams [1124]) or when natively expressed in vascular myocytes (Jaggar [1125], Wang [1126], Wang [1127]) and carotid body glomus cells (Riesco-Fagundo [1128]).

BK channels are activated by voltage, intracellular Ca2+ and Mg2+ (Fig. 1 a, b in Yang [167], Larorre [1129], Magleby [1130], Hou [1131]).



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Hemoxygenase (hemeoxygenase-2; HO-2) is a protein partner closely associated with the BKCa channel complex (Williams [1124]).

A motif in the S9–S10 part of the C-terminal of Slo1 is essential for CO activation. (Williams [166])

Sequence homology and experimental evidence suggest that the structure of the voltage sensor domain (VSD) in BK channels may resemble that of other Kv channels19, while the cytoplasmic domain of BK channels may adopt a similar structure as that of the MthK channel (Jiang [625], Hou [1131], Shi [1132], Yang [1133], Jiang [625], Fodor [1134]). Previous studies on Mg2+-dependent activation of BK channels have revealed structural details that are important for BK channel function. Particularly, two acidic amino acids (Glu374 and Glu399) in the cytoplasmic RCK1 domain of BK channel may contribute to Mg2+ coordination (Yang [1134], Xiao [1136]). Removal of the side chain carboxylate groups from these two residues completely abolishes Mg2+ sensing. These residues in the cytoplasmic domain are located close to the C-terminus of the transmembrane segment S4, enabling the bound Mg2+ to engage in an electrostatic interaction with the voltage-sensing residue Arg213 at the C-terminus of S414 (Fig. 1c in Yang [167]).





Slo1 is natively expressed in vascular myocytes ( Jaggar [1125], Wang [1126], Wang [1127]) and carotid body glomus cells (Riesco-Fagundo [1128]).



Regulation by CO of BKCa channels is emerging as a widespread and physiologically important phenomenon that is intimately involved in the control of smooth muscle contractility (both systemic and pulmonary) and excitability of neurosecretory and neuronal cell populations. (Williams [166])







Avdonin V et al. Stimulatory action of internal protons on Slo1 BK channels.
Biophys. J., 2003 May , 84 (2969-80).


Mg2+ enhances voltage sensor/gate coupling in BK channels.
J. Gen. Physiol., 2008 Jan , 131 (13-32).

Jaggar JH et al. Heme is a carbon monoxide receptor for large-conductance Ca2+-activated K+ channels.
Circ. Res., 2005 Oct 14 , 97 (805-12).

Williams SE et al. Hemoxygenase-2 is an oxygen sensor for a calcium-sensitive potassium channel.
Science, 2004 Dec 17 , 306 (2093-7).

Magleby KL Gating mechanism of BK (Slo1) channels: so near, yet so far.
J. Gen. Physiol., 2003 Feb , 121 (81-96).


Jiang Y et al. Crystal structure and mechanism of a calcium-gated potassium channel.
Nature, 2002 May 30 , 417 (515-22).

Shi J et al. Mechanism of magnesium activation of calcium-activated potassium channels.
Nature, 2002 Aug 22 , 418 (876-80).

Yang H et al. Mg2+ mediates interaction between the voltage sensor and cytosolic domain to activate BK channels.
Proc. Natl. Acad. Sci. U.S.A., 2007 Nov 13 , 104 (18270-5).

Fodor AA et al. Statistical limits to the identification of ion channel domains by sequence similarity.
J. Gen. Physiol., 2006 Jun , 127 (755-66).

Yang H et al. Tuning magnesium sensitivity of BK channels by mutations.
Biophys. J., 2006 Oct 15 , 91 (2892-900).



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