title: Altered contractile phenotypes of intestinal smooth muscle in mice deficient in myosin phosphatase target subunit 1.
abstract: OBJECTIVE
  The regulatory subunit of myosin light chain phosphatase, MYPT1, has been proposed to control smooth muscle contractility by regulating phosphorylation of the Ca(2+)-dependent myosin regulatory light chain. We generated mice with a smooth muscle-specific deletion of MYPT1 to investigate its physiologic role in intestinal smooth muscle contraction.
  
  
  METHODS
  We used the Cre-loxP system to establish Mypt1-floxed mice, with the promoter region and exon 1 of Mypt1 flanked by 2 loxP sites. These mice were crossed with SMA-Cre transgenic mice to generate mice with smooth muscle-specific deletion of MYPT1 (Mypt1(SMKO) mice). The phenotype was assessed by histologic, biochemical, molecular, and physiologic analyses.
  
  
  RESULTS
  Young adult Mypt1(SMKO) mice had normal intestinal motility in vivo, with no histologic abnormalities. On stimulation with KCl or acetylcholine, intestinal smooth muscles isolated from Mypt1(SMKO) mice produced robust and increased sustained force due to increased phosphorylation of the myosin regulatory light chain compared with muscle from control mice. Additional analyses of contractile properties showed reduced rates of force development and relaxation, and decreased shortening velocity, compared with muscle from control mice. Permeable smooth muscle fibers from Mypt1(SMKO) mice had increased sensitivity and contraction in response to Ca(2+).
  
  
  CONCLUSIONS
  MYPT1 is not essential for smooth muscle function in mice but regulates the Ca(2+) sensitivity of force development and contributes to intestinal phasic contractile phenotype. Altered contractile responses in isolated tissues could be compensated by adaptive physiologic responses in vivo, where gut motility is affected by lower intensities of smooth muscle stimulation for myosin phosphorylation and force development.
authors.affiliation: Model Animal Research Center and MOE Key Laboratory of Model Animal for Disease Study, Nanjing University, Nanjing, China.
authors.forename: Wei-Qi
authors.initials: WQ
authors.lastname: He
authors.forename: Yan-Ning
authors.initials: YN
authors.lastname: Qiao
authors.forename: Ya-Jing
authors.initials: YJ
authors.lastname: Peng
authors.forename: Juan-Min
authors.initials: JM
authors.lastname: Zha
authors.forename: Cheng-Hai
authors.initials: CH
authors.lastname: Zhang
authors.forename: Chen
authors.initials: C
authors.lastname: Chen
authors.forename: Cai-Ping
authors.initials: CP
authors.lastname: Chen
authors.forename: Pei
authors.initials: P
authors.lastname: Wang
authors.forename: Xiao
authors.initials: X
authors.lastname: Yang
authors.forename: Chao-Jun
authors.initials: CJ
authors.lastname: Li
authors.forename: Kristine E
authors.initials: KE
authors.lastname: Kamm
authors.forename: James T
authors.initials: JT
authors.lastname: Stull
authors.forename: Min-Sheng
authors.initials: MS
authors.lastname: Zhu
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000235:genetics / Q000502:physiology*; D005260:Female; D005769:Gastrointestinal Motility / Q000235:genetics / Q000502:physiology*; D007422:Intestines / Q000502:physiology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009119:Muscle Contraction / Q000235:genetics / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology*; D009219:Myosin-Light-Chain Kinase / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D043263:Myosin-Light-Chain Phosphatase
chemical_list: D009219:Myosin-Light-Chain Kinase; D043263:Myosin-Light-Chain Phosphatase; C510645:Ppp1r12a protein, mouse; D002118:Calcium