Maximum speed of shortening and ATPase activity in atrial and ventricular myocardia of hyperthyroid rats

Bottinelli, Roberto; Canepari, Monica; Cappelli, V.; Reggiani, Carlo

doi:10.1152/ajpcell.1995.269.3.c785

Cited by 34 publications

(15 citation statements)

References 27 publications

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“…In this study, we altered the ventricular expression of MHC, which is the molecular motor that largely determines myocyte contractile behavior, such that rat ventricles only expressed the slow ␤-MHC isoform. Consistent with previous studies (1,8,18,26), we showed that increased ␤-MHC expression significantly slowed V o and slowed the rates of cross-bridge cycling in the skinned myocardium (Figs. 3 and 4).…”

Section: Dependence Of Global LV Mechanical Performance On Mhc Isoforsupporting

confidence: 92%

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Altered in vivo left ventricular torsion and principal strains in hypothyroid rats

Chen

Somji²,

Yu³

et al. 2010

American Journal of Physiology-Heart and Circulatory Physiology

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Altered in vivo left ventricular torsion and principal strains in hypothyroid rats. Am J Physiol Heart Circ Physiol 299: H1577-H1587, 2010. First published August 20, 2010 doi:10.1152/ajpheart.00406.2010.-The twisting and untwisting motions of the left ventricle (LV) lead to efficient ejection of blood during systole and filling of the ventricle during diastole. Global LV mechanical performance is dependent on the contractile properties of cardiac myocytes; however, it is not known how changes in contractile protein expression affect the pattern and timing of LV rotation. At the myofilament level, contractile performance is largely dependent on the isoforms of myosin heavy chain (MHC) that are expressed. Therefore, in this study, we used MRI to examine the in vivo mechanical consequences of altered MHC isoform expression by comparing the contractile properties of hypothyroid rats, which expressed only the slow ␤-MHC isoform, and euthyroid rats, which predominantly expressed the fast ␣-MHC isoform. Unloaded shortening velocity (Vo) and apparent rate constants of force development (ktr) were measured in the skinned ventricular myocardium isolated from euthyroid and hypothyroid hearts. Increased expression of ␤-MHC reduced LV torsion and fiber strain and delayed the development of peak torsion and strain during systole. Depressed in vivo mechanical performance in hypothyroid rats was related to slowed cross-bridge performance, as indicated by significantly slower Vo and ktr, compared with euthyroid rats. Dobutamine infusion in hypothyroid hearts produced smaller increases in torsion and strain and aberrant transmural torsion patterns, suggesting that the myocardial response to ␤-adrenergic stress is compromised. Thus, increased expression of ␤-MHC alters the pattern and decreases the magnitude of LV rotation, contributing to reduced mechanical performance during systole, especially in conditions of increased workload. magnetic resonance imaging; myosin heavy chain; myocardial contractility; dobutamine; cardiac muscle contraction DURING THE EARLY PHASE of isovolumic contraction, the ventricular apex and base initially rotate in a counterclockwise direction when viewed from the apex to base (55), and later in systole, the base rotates in a clockwise direction, whereas the apex continues to rotate in a counterclockwise direction (36). Toward the end of systole and early diastole, the direction of torsion is reversed as the ventricle untwists (51, 56). The systolic twisting and diastolic untwisting of the left ventricle (LV) optimize the ejection of blood and the filling of the chamber during systole and diastole, respectively. The pattern of ventricular rotation during systole and diastole is facilitated by the architectural design of the LV, in which the subendocardial fibers are oriented in a right-handed helix and the epicardial fibers in an opposing left-handed helix (64), creating the torsion associated with the wringing and unwringing motions of the heart. The sequence of electromechanical activation occurs in ...

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Section: Dependence Of Global LV Mechanical Performance On Mhc Isoforsupporting

confidence: 92%

“…Consistent with previous findings (1,8,18,26), we found that decreased expression of ␣-MHC significantly reduced V o , as values were approximately twofold slower in the hypothyroid myocardium compared with the euthyroid myocardium (Fig. 4).…”

Section: Effects Of Altered Mhc Expression On Mechanical Properties Osupporting

confidence: 92%

Altered in vivo left ventricular torsion and principal strains in hypothyroid rats

Chen

Somji²,

Yu³

et al. 2010

American Journal of Physiology-Heart and Circulatory Physiology

View full text Add to dashboard Cite

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“…Tension was normalized by cross-sectional area. The unloaded maximum velocity of shortening (V max ) was extrapolated from zero loading condition according to the Maxwell model of muscle (32).…”

Section: Methodsmentioning

confidence: 99%

A Proteolytic NH2-terminal Truncation of Cardiac Troponin I That Is Up-regulated in Simulated Microgravity

Zhang

Jin

2001

Journal of Biological Chemistry

108

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In a tail suspension rat model, we investigated changes in myofilament protein during cardiac adaptation in simulated microgravity. Contractile force and velocity of cardiac muscle were decreased in the tail suspension rats as compared with the control. Ca 2؉ -dependent actomyosin ATPase activity was also decreased; however, sensitivity of cardiac muscle to Ca 2؉ activation was unchanged. There was no change in expression of myosin heavy chain, tropomyosin, troponin T, or troponin I isoforms in hearts of tail suspension rats. A novel finding is a fragment of cardiac troponin I (cTnI) that had increased amounts in the heart of tail suspension rats. Binding of this cTnI fragment by a monoclonal antibody that specifically recognizes the COOH terminus indicates an intact COOH terminus.

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“…Ventricular MLC isoforms are associated with 1.2-1.8 times slower shortening velocities than atrial MLC isoforms in mouse [9,41], rat [6], and human [32]. In contrast, no clear dependence of ATPase activity on MLC isoforms was observed [6,21,41].…”

Section: Introductionmentioning

confidence: 91%

Fine-tuning of cross-bridge kinetics in cardiac muscle of rat and mouse by myosin light chain isoforms

Andruchov

Andruchova

Galler

2006

Pflugers Arch - Eur J Physiol

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Cross-bridge kinetics underlying stretch-induced force transients was studied in cardiac muscle strips with different myosin heavy chain (MHC) and myosin light chain (MLC) isoforms. The force transients were induced by stepwise stretches of maximally Ca(2+)-activated skinned muscle strips. The MHC and MLC isoforms were analyzed by electrophoreses after the mechanical experiments. Muscle strips of euthyroid rats and mice exclusively containing alpha-MHC were used. In addition, muscle strips of hyper- and hypothyroid rats containing different combinations of MHC and MLC isoforms were used. The thyroid hormone is known to alter the expression of MHC but not of MLC isoforms. In muscle strips containing exclusively alpha-MHC, atrial MLC isoforms (all atria of rats and mice) were associated with about 30% faster kinetics than ventricular MLC isoforms (ventricles of hyperthyroid rats and some muscle strips of ventricles of euthyroid rats and mice). On the other hand, in muscle strips containing exclusively ventricular MLC isoforms, alpha-MHC (ventricles of hyperthyroid rats) was associated with about 2.6 times faster kinetics than beta-MHC (ventricles of hypothyroid rats). We conclude that the MLC isoforms fine-tune cross-bridge kinetics, which underlies stretch-induced force transients, whereas the MHC isoforms mainly determine this kinetics. The effect of MLC isoforms on the cross-bridge kinetics may partially contribute to the faster twitch contraction in atria than in ventricles. Furthermore, it may play a role in various cardiomyopathies where atrial MLC isoforms are partially expressed in ventricles or ventricular MLC isoforms are partially expressed in atria.

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Maximum speed of shortening and ATPase activity in atrial and ventricular myocardia of hyperthyroid rats

Cited by 34 publications

References 27 publications

Altered in vivo left ventricular torsion and principal strains in hypothyroid rats

Altered in vivo left ventricular torsion and principal strains in hypothyroid rats

A Proteolytic NH2-terminal Truncation of Cardiac Troponin I That Is Up-regulated in Simulated Microgravity

Fine-tuning of cross-bridge kinetics in cardiac muscle of rat and mouse by myosin light chain isoforms

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