title: SMB myosin heavy chain knockout enhances tonic contraction and reduces the rate of force generation in ileum and stomach antrum.
abstract: The role of SMA and SMB smooth muscle myosin heavy chain (MHC) isoforms in tonic and phasic contractions was studied in phasic (longitudinal ileum and stomach circular antrum) and tonic (stomach circular fundus) smooth muscle tissues of SMB knockout mice. Knocking out the SMB MHC gene eliminated SMB MHC protein expression and resulted in upregulation of the SMA MHC protein without altering the total MHC protein level. Switching from SMB to SMA MHC protein expression decreased the rate of the force transient and increased the sustained tonic force in SMB((-/-)) ileum and antrum with high potassium (KPSS) but not with carbachol (CCh) stimulation. The increased tonic contraction under the depolarized condition was not through changes in second messenger signaling pathways (PKC/CPI-17 or Rho/ROCK signaling pathway) or LC(20) phosphorylation. Biochemical analyses showed that the expression of contractile regulatory proteins (MLCK, MLCP, PKCδ, and CPI-17) did not change significantly in tissues tested except for PKCα protein expression being significantly decreased in the SMB((-/-)) antrum. However, specifically activating PKCα with phorbol dibutyrate (PDBu) was not significantly different in knockout and wild-type tissues, with total force being a fraction of the force generation with KPSS or CCh stimulation in SMB((-/-)) ileum and antrum. Taken together, these data show removing the SMB MHC protein expression with a compensatory increase in the SMA MHC protein results in enhanced sustained KPSS-induced tonic contraction with a reduced rate of force generation in these phasic tissues.
authors.affiliation: Department of Biological Sciences, Marquette University, Milwaukee, WI, 53201, USA.
authors.forename: Qian
authors.initials: Q
authors.lastname: Huang
authors.forename: Gopal J
authors.initials: GJ
authors.lastname: Babu
authors.forename: Muthu
authors.initials: M
authors.lastname: Periasamy
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Eddinger
mesh_terms: D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D007082:Ileum / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D053580:Muscle Strength / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010766:Phosphorylation; D011188:Potassium / Q000494:pharmacology; D051571:Protein Kinase C-alpha / Q000096:biosynthesis / Q000502:physiology; D011706:Pyloric Antrum / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D015290:Second Messenger Systems / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D024745:Smooth Muscle Myosins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*
chemical_list: D018679:Cholinergic Agonists; D015240:Phorbol 12,13-Dibutyrate; D002217:Carbachol; D051571:Protein Kinase C-alpha; D024745:Smooth Muscle Myosins; D018995:Myosin Heavy Chains; D011188:Potassium