Myosin heavy chain and cardiac troponin T damage is associated with impaired myofibrillar ATPase activity contributing to sarcomeric dysfunction in Ca 2+ -paradox rat hearts

• Published in: Molecular and cellular biochemistry 2017-06, Vol.430 (1-2), p.57
• Main Authors: Kovács, Árpád, Kalász, Judit, Pásztor, Enikő T, Tóth, Attila, Papp, Zoltán, Dhalla, Naranjan S, Barta, Judit
• Format: Article
• Language: English
• Subjects: Animals; Calcium - metabolism; Male; Myocardial Contraction; Myocardium - metabolism; Myocardium - pathology; Myosin Heavy Chains - metabolism; Rats; Rats, Sprague-Dawley; Sarcomeres - metabolism; Sarcomeres - pathology; Troponin T - metabolism
• ISSN: 1573-4919

This study aimed to explore the potential contribution of myofibrils to contractile dysfunction in Ca -paradox hearts. Isolated rat hearts were perfused with Krebs-Henseleit solution (Control), followed by Ca -depletion, and then Ca -repletion after Ca -depletion (Ca -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 Ca -depletion (9.8 ± 1.3 mmHg) and Ca -paradox (12.9 ± 1.3 mmHg) with similar decline in +dP/dt and -dP/dt. LVEDP was increased in both Ca -depletion and Ca -paradox. Compared to Control, myofibrillar Ca -stimulated ATPase activity was decreased in the Ca -depletion group (12.08 ± 0.57 vs. 8.13 ± 0.19 µmol P /mg protein/h), besides unvarying Mg ATPase activity, while upon Ca -paradox myofibrillar Ca -stimulated ATPase activity was decreased (12.08 ± 0.57 vs. 8.40 ± 0.22 µmol P /mg protein/h), but Mg ATPase activity was increased (3.20 ± 0.25 vs. 7.21 ± 0.36 µmol P /mg protein/h). In force measurements of isolated cardiomyocytes at saturating [Ca ], Ca -depleted cells had lower rate constant of force redevelopment (k , 3.85 ± 0.21) and unchanged active tension, while those in Ca -paradox produced lower active tension (12.12 ± 3.19 kN/m ) and k (3.21 ± 23) than cells of Control group (25.07 ± 3.51 and 4.61 ± 22 kN/m , respectively). In biochemical assays, α-myosin heavy chain and cardiac troponin T presented progressive degradation during Ca -depletion and Ca -paradox. Our results suggest that contractile impairment in Ca -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 Ca -paradoxical hearts is apparently not related to titin, rather explained by the altered myofibrillar ATPase activity.