Potassium channels play a key role in the transmission of information within the neuromuscular system by translating ionic fluxes across cellular membrane into electrical impulses and by interconverting and transducing electrical and chemical signals. Among this class of polypeptides, K+ channels represent the most extensive and diverse group. While all K+ channels are alike in their selective permeability to K+ over other monovalent ions, they can be subdivided into 2 distinct types: voltage-activated K+ channels, which respond to changes in membrane potential, and Ca(2+)-activated K+ channels, which respond primarily to increases in intracellular calcium ion concentrations. The first structural gene of a calcium-activated potassium channel was isolated through study of mutations of the Drosophila 'slowpoke' (slo) locus, which were found specifically to eliminate a fast, calcium-activated potassium current in adult and larval muscles and in larval neurons. The large conductance, calcium-activated potassium (BK) channel is a member of the Shaker-related 6-transmembrane domain potassium channel superfamily that is sensitive to voltage and calcium. BK channels are composed of a pore-forming alpha subunit (KCNMA1, or HSLO; OMIM 600150) and, in some tissues, a beta subunit.
NCBI Summary:
MaxiK channels are large conductance, voltage and calcium-sensitive potassium channels which 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. At least two transcript variants encoding different isoforms have been found for this gene, but the full-length nature of only one of them has been described.
General function
Channel/transport protein
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Cellular localization
Plasma membrane
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Ovarian function
Luteinization
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Expression regulated by
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Ovarian localization
Granulosa, Luteal cells
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Kunz L, et al reported
Ca2+-activated, large conductance K+ channel in the
ovary: identification, characterization, and functional
involvement in steroidogenesis.
Progesterone production by the corpus luteum is a process vital for
reproduction. In humans its secretion is stimulated by the placental
hormone human chorionic gonadotropin (hCG), and this stimulatory
action can also be observed in cultured human luteinized granulosa cells
(GCs). The authors provide evidence that opening of a Ca(2+)-activated
K(+) channel, the BK(Ca), is crucially involved in this process.
Immunohistochemistry and RT-PCR revealed the presence of the
pore-forming alpha-subunit in human luteinized GCs and in luteal cells of
human, macaque, and rat, implying that BK(Ca) channels are important
throughout species. Blocking of BK(Ca) channels by iberiotoxin
attenuated hCG-induced progesterone secretion. The inhibitory action of
iberiotoxin suggests that BK(Ca) channels are activated in the course of
hCG-induced steroidogenesis. Electrophysiological approach precludes a direct
regulation of channel activity by hCG or GC-derived steroids
(progesterone and 17beta-estradiol). Instead, the peptide hormone
oxytocin and an acetylcholine (ACh) agonist, carbachol, evoked transient
BK(Ca) currents and membrane hyperpolarization. These two molecules
are both secreted by GCs and act via raised intracellular Ca(2+) levels.
The release of oxytocin is stimulated by hCG, and a similar mechanism is
likely in the case of ACh. It was concluded that BK(Ca) channel activity in
GCs is mediated by components of the intraovarian signaling system,
thereby interlinking a systemic hormonal and a local neuroendocrine
system in control of steroidogenesis.