title: Synergistic role of ADP and Ca(2+) in diastolic myocardial stiffness.
abstract: Diastolic dysfunction in heart failure patients is evident from stiffening of the passive properties of the ventricular wall. Increased actomyosin interactions may significantly limit diastolic capacity, however, direct evidence is absent. From experiments at the cellular and whole organ level, in humans and rats, we show that actomyosin-related force development contributes significantly to high diastolic stiffness in environments where high ADP and increased diastolic [Ca(2+) ] are present, such as the failing myocardium. Our basal study provides a mechanical mechanism which may partly underlie diastolic dysfunction. Heart failure (HF) with diastolic dysfunction has been attributed to increased myocardial stiffness that limits proper filling of the ventricle. Altered cross-bridge interaction may significantly contribute to high diastolic stiffness, but this has not been shown thus far. Cross-bridge interactions are dependent on cytosolic [Ca(2+) ] and the regeneration of ATP from ADP. Depletion of myocardial energy reserve is a hallmark of HF leading to ADP accumulation and disturbed Ca(2+) handling. Here, we investigated if ADP elevation in concert with increased diastolic [Ca(2+) ] promotes diastolic cross-bridge formation and force generation and thereby increases diastolic stiffness. ADP dose-dependently increased force production in the absence of Ca(2+) in membrane-permeabilized cardiomyocytes from human hearts. Moreover, physiological levels of ADP increased actomyosin force generation in the presence of Ca(2+) both in human and rat membrane-permeabilized cardiomyocytes. Diastolic stress measured at physiological lattice spacing and 37°C in the presence of pathological levels of ADP and diastolic [Ca(2+) ] revealed a 76 ± 1% contribution of cross-bridge interaction to total diastolic stress in rat membrane-permeabilized cardiomyocytes. Inhibition of creatine kinase (CK), which increases cytosolic ADP, in enzyme-isolated intact rat cardiomyocytes impaired diastolic re-lengthening associated with diastolic Ca(2+) overload. In isolated Langendorff-perfused rat hearts, CK inhibition increased ventricular stiffness only in the presence of diastolic [Ca(2+) ]. We propose that elevations of intracellular ADP in specific types of cardiac disease, including those where myocardial energy reserve is limited, contribute to diastolic dysfunction by recruiting cross-bridges, even at low Ca(2+) , and thereby increase myocardial stiffness.
authors.affiliation: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, The Netherlands.
authors.forename: Vasco
authors.initials: V
authors.lastname: Sequeira
authors.affiliation: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, The Netherlands.
authors.forename: Aref
authors.initials: A
authors.lastname: Najafi
authors.affiliation: Sarver Heart Center, University of Arizona, Tucson, AZ, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: McConnell
authors.affiliation: School of Biomedical Sciences, Garstang Building, University of Leeds, Leeds, UK.
authors.forename: Ewan D
authors.initials: ED
authors.lastname: Fowler
authors.affiliation: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, The Netherlands.
authors.forename: Ilse A E
authors.initials: IA
authors.lastname: Bollen
authors.affiliation: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, The Netherlands.
authors.forename: Rob C I
authors.initials: RC
authors.lastname: Wüst
authors.affiliation: Muscle Research Unit, Bosch Institute, University of Sydney, Sydney, Australia.
authors.forename: Cris
authors.initials: C
authors.lastname: dos Remedios
authors.affiliation: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, The Netherlands.
authors.forename: Michiel
authors.initials: M
authors.lastname: Helmes
authors.affiliation: School of Biomedical Sciences, Garstang Building, University of Leeds, Leeds, UK.
authors.forename: Ed
authors.initials: E
authors.lastname: White
authors.affiliation: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, The Netherlands.|Department of Physics and Astronomy, VU University, Amsterdam, The Netherlands.
authors.forename: Ger J M
authors.initials: GJ
authors.lastname: Stienen
authors.affiliation: Sarver Heart Center, University of Arizona, Tucson, AZ, USA.
authors.forename: Jil
authors.initials: J
authors.lastname: Tardiff
authors.affiliation: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, The Netherlands.
authors.forename: Diederik W D
authors.initials: DW
authors.lastname: Kuster
authors.affiliation: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, The Netherlands.|ICIN-Netherlands Heart Institute, Utrecht, The Netherlands.
authors.forename: Jolanda
authors.initials: J
authors.lastname: van der Velden
mesh_terms: D000205:Actomyosin / Q000502:physiology; D000244:Adenosine Diphosphate / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002311:Cardiomyopathy, Dilated / Q000503:physiopathology; D003402:Creatine Kinase / Q000037:antagonists & inhibitors / Q000502:physiology; D003971:Diastole; D006321:Heart / Q000502:physiology*; D006801:Humans; D007460:Iodoacetamide / Q000494:pharmacology; D007537:Isometric Contraction; D008297:Male; D032383:Myocytes, Cardiac / Q000502:physiology; D017208:Rats, Wistar
chemical_list: D000244:Adenosine Diphosphate; D000205:Actomyosin; D003402:Creatine Kinase; D002118:Calcium; D007460:Iodoacetamide