title: Myosin heavy chain and cardiac troponin T damage is associated with impaired myofibrillar ATPase activity contributing to sarcomeric dysfunction in Ca2+-paradox rat hearts.
abstract: This study aimed to explore the potential contribution of myofibrils to contractile dysfunction in Ca2+-paradox hearts. Isolated rat hearts were perfused with Krebs-Henseleit solution (Control), followed by Ca2+-depletion, and then Ca2+-repletion after Ca2+-depletion (Ca2+-paradox) by Langendorff method. During heart perfusion left ventricular developed pressure (LVDP), end-diastolic pressure (LVEDP), rate of pressure development (+ dP/dt), and pressure decay (-dP/dt) were registered. Control LVDP (127.4 ± 6.1 mmHg) was reduced during Ca2+-depletion (9.8 ± 1.3 mmHg) and Ca2+-paradox (12.9 ± 1.3 mmHg) with similar decline in +dP/dt and -dP/dt. LVEDP was increased in both Ca2+-depletion and Ca2+-paradox. Compared to Control, myofibrillar Ca2+-stimulated ATPase activity was decreased in the Ca2+-depletion group (12.08 ± 0.57 vs. 8.13 ± 0.19 µmol Pi/mg protein/h), besides unvarying Mg2+ATPase activity, while upon Ca2+-paradox myofibrillar Ca2+-stimulated ATPase activity was decreased (12.08 ± 0.57 vs. 8.40 ± 0.22 µmol Pi/mg protein/h), but Mg2+ATPase activity was increased (3.20 ± 0.25 vs. 7.21 ± 0.36 µmol Pi/mg protein/h). In force measurements of isolated cardiomyocytes at saturating [Ca2+], Ca2+-depleted cells had lower rate constant of force redevelopment (ktr,max, 3.85 ± 0.21) and unchanged active tension, while those in Ca2+-paradox produced lower active tension (12.12 ± 3.19 kN/m2) and ktr,max(3.21 ± 23) than cells of Control group (25.07 ± 3.51 and 4.61 ± 22 kN/m2, respectively). In biochemical assays, α-myosin heavy chain and cardiac troponin T presented progressive degradation during Ca2+-depletion and Ca2+-paradox. Our results suggest that contractile impairment in Ca2+-paradox partially resides in deranged sarcomeric function and compromised myofibrillar ATPase activity as a result of myofilament protein degradation, such as α-myosin heavy chain and cardiac troponin T. Impaired relaxation seen in Ca2+-paradoxical hearts is apparently not related to titin, rather explained by the altered myofibrillar ATPase activity.
authors.affiliation: Division of Clinical Physiology, Institute of Cardiology, Faculty of Medicine, University of Debrecen, Debrecen, 4032, Hungary.
authors.forename: Árpád
authors.initials: Á
authors.lastname: Kovács
authors.affiliation: Division of Clinical Physiology, Institute of Cardiology, Faculty of Medicine, University of Debrecen, Debrecen, 4032, Hungary.
authors.forename: Judit
authors.initials: J
authors.lastname: Kalász
authors.affiliation: Division of Clinical Physiology, Institute of Cardiology, Faculty of Medicine, University of Debrecen, Debrecen, 4032, Hungary.
authors.forename: Enikő T
authors.initials: ET
authors.lastname: Pásztor
authors.affiliation: Division of Clinical Physiology, Institute of Cardiology, Faculty of Medicine, University of Debrecen, Debrecen, 4032, Hungary.|Research Centre for Molecular Medicine, Faculty of Medicine, University of Debrecen, Debrecen, 4032, Hungary.
authors.forename: Attila
authors.initials: A
authors.lastname: Tóth
authors.affiliation: Division of Clinical Physiology, Institute of Cardiology, Faculty of Medicine, University of Debrecen, Debrecen, 4032, Hungary.|Research Centre for Molecular Medicine, Faculty of Medicine, University of Debrecen, Debrecen, 4032, Hungary.
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Papp
authors.affiliation: Department of Physiology and Pathophysiology, Faculty of Health Sciences, St. Boniface Hospital Albrechtsen Research Centre, Institute of Cardiovascular Sciences, College of Medicine, University of Manitoba, 351 Tache Avenue, Winnipeg, MB, R2H 2A6, Canada.
authors.forename: Naranjan S
authors.initials: NS
authors.lastname: Dhalla
authors.affiliation: Department of Physiology and Pathophysiology, Faculty of Health Sciences, St. Boniface Hospital Albrechtsen Research Centre, Institute of Cardiovascular Sciences, College of Medicine, University of Manitoba, 351 Tache Avenue, Winnipeg, MB, R2H 2A6, Canada. bartajud@gmail.com.|Department of Cardiology, Institute of Cardiology, Faculty of Medicine, University of Debrecen, 22 Móricz Zs krt., Debrecen, 4032, Hungary. bartajud@gmail.com.
authors.forename: Judit
authors.identifier: http://orcid.org/0000-0002-3010-7373
authors.initials: J
authors.lastname: Barta
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D008297:Male; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D018995:Myosin Heavy Chains / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012518:Sarcomeres / Q000378:metabolism* / Q000473:pathology; D020107:Troponin T / Q000378:metabolism*
chemical_list: D020107:Troponin T; D018995:Myosin Heavy Chains; D002118:Calcium
keywords: Calcium paradox; Isolated cardiomyocytes; Myofibrillar ATPase activity; Myofilament protein degradation