title: Increased passive stiffness of cardiomyocytes in the transverse direction and residual actin and myosin cross-bridge formation in hypertrophied rat hearts induced by chronic β-adrenergic stimulation.
abstract: BACKGROUND
  Left ventricular (LV) hypertrophy is often present in patients with diastolic heart failure. However, stiffness of hypertrophied cardiomyocytes in the transverse direction has not been fully elucidated. The aim of this study was to assess passive cardiomyocyte stiffness of hypertrophied hearts in the transverse direction and the influence of actin-myosin cross-bridge formation on the stiffness.
  
  
  RESULTS
  Wistar rats received a vehicle (control) or isoproterenol (ISO) subcutaneously. After 7 days, compared with the controls, ISO administration had significantly increased heart weight and LV wall thickness and had decreased peak early annular relaxation velocity (e') assessed by echocardiography. Elastic modulus of living cardiomyocytes in the transverse direction assessed by an atomic force microscope was significantly higher in the ISO group than in controls. We added butanedione monoxime (BDM), an inhibitor of actin-myosin interaction, and blebbistatin, a specific myosin II inhibitor, to the medium. BDM and blebbistatin significantly reduced the elastic modulus of cardiomyocytes in the ISO group. X-ray diffraction analysis showed that the reflection intensity ratio (I((1,0))/I((1,1))) at diastole was not different before and after treatment with BDM, which induces complete relaxation, in control hearts, but that I((1,0))/I((1,1)) was significantly increased after BDM treatment in the ISO group, indicating residual cross-bridge formation in hypertrophied hearts.
  
  
  CONCLUSIONS
  Passive cardiomyocyte stiffness in the transverse direction is increased in hearts with ISO-induced hypertrophy and this is caused by residual actin-myosin cross-bridge formation.
authors.affiliation: Department of Cardiovascular Medicine, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan.
authors.forename: Wakako
authors.initials: W
authors.lastname: Sumita Yoshikawa
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Nakamura
authors.forename: Daiji
authors.initials: D
authors.lastname: Miura
authors.forename: Juichiro
authors.initials: J
authors.lastname: Shimizu
authors.forename: Ken
authors.initials: K
authors.lastname: Hashimoto
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Kataoka
authors.forename: Hiroko
authors.initials: H
authors.lastname: Toyota
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Okuyama
authors.forename: Toru
authors.initials: T
authors.lastname: Miyoshi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Morita
authors.forename: Kengo
authors.initials: K
authors.lastname: Fukushima Kusano
authors.forename: Tatsuhito
authors.initials: T
authors.lastname: Matsuo
authors.forename: Miyako
authors.initials: M
authors.lastname: Takaki
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Kajiya
authors.forename: Naoto
authors.initials: N
authors.lastname: Yagi
authors.forename: Tohru
authors.initials: T
authors.lastname: Ohe
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ito
mesh_terms: D000199:Actins / Q000378:metabolism*; D000318:Adrenergic beta-Agonists / Q000009:adverse effects* / Q000494:pharmacology; D000818:Animals; D006332:Cardiomegaly / Q000139:chemically induced* / Q000473:pathology / Q000503:physiopathology; D002478:Cells, Cultured; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D004195:Disease Models, Animal; D004548:Elasticity / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology; D017379:Hypertrophy, Left Ventricular / Q000139:chemically induced* / Q000473:pathology / Q000503:physiopathology; D007545:Isoproterenol / Q000009:adverse effects / Q000494:pharmacology; D008297:Male; D018625:Microscopy, Atomic Force; D032383:Myocytes, Cardiac / Q000000981:diagnostic imaging / Q000473:pathology* / Q000502:physiology; D009218:Myosins / Q000378:metabolism*; D009929:Organ Size / Q000187:drug effects; D010210:Papillary Muscles / Q000000981:diagnostic imaging / Q000187:drug effects / Q000473:pathology; D011859:Radiography; D051381:Rats; D017208:Rats, Wistar; D014463:Ultrasonography
chemical_list: D000199:Actins; D000318:Adrenergic beta-Agonists; D004791:Enzyme Inhibitors; D006576:Heterocyclic Compounds, 4 or More Rings; C004717:diacetylmonoxime; C472645:blebbistatin; D009218:Myosins; D003931:Diacetyl; D007545:Isoproterenol