title: Regulation of arterial tone by smooth muscle myosin type II.
abstract: The initiation of contractile force in arterial smooth muscle (SM) is believed to be regulated by the intracellular Ca2+ concentration and SM myosin type II phosphorylation. We tested the hypothesis that SM myosin type II operates as a molecular motor protein in electromechanical, but not in protein kinase C (PKC)-induced, contraction of small resistance-sized cerebral arteries. We utilized a SM type II myosin heavy chain (MHC) knockout mouse model and measured arterial wall Ca2+ concentration ([Ca2+](i)) and the diameter of pressurized cerebral arteries (30-100 microm) by means of digital fluorescence video imaging. Intravasal pressure elevation caused a graded [Ca2+](i) increase and constricted cerebral arteries of neonatal wild-type mice by 20-30%. In contrast, intravasal pressure elevation caused a graded increase of [Ca2+](i) without constriction in (-/-) MHC-deficient arteries. KCl (60 mM) induced a further [Ca2+](i) increase but failed to induce vasoconstriction of (-/-) MHC-deficient cerebral arteries. Activation of PKC by phorbol ester (phorbol 12-myristate 13-acetate, 100 nM) induced a strong, sustained constriction of (-/-) MHC-deficient cerebral arteries without changing [Ca2+](i). These results demonstrate a major role for SM type II myosin in the development of myogenic tone and Ca2+ -dependent constriction of resistance-sized cerebral arteries. In contrast, the sustained contractile response did not depend on myosin and intracellular Ca2+ but instead depended on PKC. We suggest that SM myosin type II operates as a molecular motor protein in the development of myogenic tone but not in pharmacomechanical coupling by PKC in cerebral arteries. Thus PKC-dependent phosphorylation of cytoskeletal proteins may be responsible for sustained contraction in vascular SM.
authors.affiliation: Franz Volhard Clinic and Max Delbrück Center for Molecular Medicine, Charité University Hospital, Humboldt University of Berlin, 13125 Berlin, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Löhn
authors.forename: Dietmar
authors.initials: D
authors.lastname: Kämpf
authors.forename: Chai
authors.initials: C
authors.lastname: Gui-Xuan
authors.forename: Hermann
authors.initials: H
authors.lastname: Haller
authors.forename: Friedrich C
authors.initials: FC
authors.lastname: Luft
authors.forename: Maik
authors.initials: M
authors.lastname: Gollasch
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002273:Carcinogens / Q000494:pharmacology; D002536:Cerebral Arteries / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D020409:Molecular Motor Proteins / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D024462:Myosin Type II / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D013314:Stress, Mechanical; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*
chemical_list: D002273:Carcinogens; D020409:Molecular Motor Proteins; D011493:Protein Kinase C; D024462:Myosin Type II; D013755:Tetradecanoylphorbol Acetate