title: Beta1-subunit of MaxiK channel in smooth muscle: a key molecule which tunes muscle mechanical activity.
abstract: The MaxiK channel is the large-conductance, voltage-dependent, and Ca(2+)-activated K(+) channel. This channel is almost ubiquitously distributed among mammalian tissues including smooth muscles. The ability of MaxiK to work as a rheostat fine tuning membrane potential and intracellular Ca(2+) enables it to mediate opposite functions: it facilitates contraction, but also acts as a negative feedback mechanism to restore tone after a contraction cycle. MaxiK activation mediates relaxations to a variety of physiological substances, whereas its inhibition plays a significant role in contractile responses. At the molecular level, MaxiK is a protein complex formed by at least two integral dissimilar membrane subunits, the pore-forming alpha-subunit and a regulatory beta-subunit. In smooth muscles, beta1 is the predominant subunit and most MaxiK seem to be assembled of alpha- and beta1-subunits. The presence of the beta1-subunit confers MaxiK with higher Ca(2+)/voltage sensitivity, which makes this channel an efficient tuner of smooth muscle functions in physiological conditions. The enhanced smooth muscle mechanical activities in mice lacking the beta1-subunit gene support the principal role of this channel molecular component in tissue and whole animal functions. In this review, we discuss MaxiK channel roles as a tuner of smooth muscle contractility, especially focusing attention on the modulatory beta1-subunit.
authors.affiliation: Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Chiba, Japan. yotanaka@phar.toho-u.ac.jp
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Katsuo
authors.initials: K
authors.lastname: Koike
authors.forename: Abderrahmane
authors.initials: A
authors.lastname: Alioua
authors.forename: Koki
authors.initials: K
authors.lastname: Shigenobu
authors.forename: Enrico
authors.initials: E
authors.lastname: Stefani
authors.forename: Ligia
authors.initials: L
authors.lastname: Toro
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D006801:Humans; D015640:Ion Channel Gating; D008564:Membrane Potentials; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology*; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics; D017434:Protein Structure, Tertiary
chemical_list: D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D020033:Protein Isoforms; D002118:Calcium