Effect of length and cross-bridge attachment on Ca2+ binding to cardiac troponin C

The sensitivity of skinned cardiac muscle bundles to Ca2+ is a function of sarcomere length. Ca2+ sensitivity is increased as fiber length is extended along the ascending limb of the force-length curve and it has been suggested that this phenomenon makes a major contribution to the steep force-length relationship that exists in living cardiac muscle. To gain greater insight into the mechanism behind the length dependence of Ca2+ sensitivity isotopic measurements of Ca2+ binding to detergent-extracted bovine, ventricular muscle bundles were made under conditions in which troponin C was the only major Ca2+ binding species. Experiments were designed to determine whether 1) Ca2+-troponin C affinity varies in the sarcomere length range corresponding to the ascending limb of the force-length curve, and 2) Ca2+ binding correlates with length per se or with changes in the number of length-dependent cross-bridge attachments. Measurements were made of Ca2+ binding in the rigor and relaxed states. The latter state was produced by suppressing actin-myosin interaction with the phosphate analogue, sodium vanadate. After vanadate treatment it is possible to obtain a complete Ca2+ saturation curve in the presence of physiological MgATP concentrations and at constant sarcomere length. The results show that the binding of Ca2+ to the regulatory site of cardiac troponin C is length dependent but this length dependence is actually a dependence on the number of attached cross bridges.

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Coupling calcium binding to troponin C and cross-bridge cycling in skinned cardiac cells

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1994.266.3.h1260 ◽

1994 ◽

Vol 266 (3) ◽

pp. H1260-H1271 ◽

Cited By ~ 22

Author(s):

A. Landesberg ◽

S. Sideman

Keyword(s):

Cardiac Muscle ◽

Calcium Binding ◽

Troponin C ◽

Cardiac Cells ◽

Loose Coupling ◽

Cross Bridge ◽

Length Relationship ◽

Troponin Complex ◽

Cross Bridges

This study examines the coupling of calcium binding to troponin with the force developed by the cross bridges in the skinned cardiac muscle. It emphasizes the key role of the troponin complex in regulating cross-bridge cycling and defines four distinct states of the troponin complex in the single-overlap region. These include a "loose-coupling" state, wherein cross bridges can exist in the strong conformation without having calcium bound to the neighbor troponin C. Published simultaneous measurements of the force and the bound calcium are used to calculate the apparent calcium binding coefficients. The force-length relationships at different free calcium concentrations are used to evaluate the cooperative mechanism. The dependence of the affinity of troponin for calcium on the number of force-generating cross bridges is the dominant cooperative mechanism. The proposed loose-coupling model, with a positive feedback of force on calcium binding, describes the role of calcium in force regulation and the force-length relationship in skinned cardiac muscle. The ability to simulate the rate of force development is demonstrated.

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Regulation of energy consumption in cardiac muscle: analysis of isometric contractions

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1999.276.3.h998 ◽

1999 ◽

Vol 276 (3) ◽

pp. H998-H1011 ◽

Cited By ~ 10

Author(s):

Amir Landesberg ◽

Samuel Sideman

Keyword(s):

Energy Consumption ◽

Cardiac Muscle ◽

Feedback Mechanism ◽

Isometric Contractions ◽

Cross Bridge ◽

Time Integral ◽

Length Relationship ◽

Cross Bridges ◽

Force Time ◽

Force Time Integral

The well-known linear relationship between oxygen consumption and force-length area or the force-time integral is analyzed here for isometric contractions. The analysis, which is based on a biochemical model that couples calcium kinetics with cross-bridge cycling, indicates that the change in the number of force-generating cross bridges with the change in the sarcomere length depends on the force generated by the cross bridges. This positive-feedback phenomenon is consistent with our reported cooperativity mechanism, whereby the affinity of the troponin for calcium and, hence, cross-bridge recruitment depends on the number of force-generating cross bridges. Moreover, it is demonstrated that a model that does not include a feedback mechanism cannot describe the dependence of energy consumption on the loading conditions. The cooperativity mechanism, which has been shown to determine the force-length relationship and the related Frank-Starling law, is shown here to provide the basis for the regulation of energy consumption in the cardiac muscle.

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Dynamic and Structural Allosteric Events between the D/E Linker and N-Domain of Cardiac Troponin C Reveal a Novel Mechanism for Cardiac Muscle Regulation

Biophysical Journal ◽

10.1016/j.bpj.2018.11.2634 ◽

2019 ◽

Vol 116 (3) ◽

pp. 488a

Author(s):

Mayra A. Marques ◽

Guilherme A.P. de Oliveira ◽

Adolfo H. Moraes ◽

Maicom Landim-Vieira ◽

Karissa D. Jones ◽

...

Keyword(s):

Cardiac Muscle ◽

Cardiac Troponin ◽

Troponin C ◽

Muscle Regulation ◽

Cardiac Troponin C ◽

Cardiac Muscle Regulation

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Hypertrophic Cardiomyopathy Cardiac Troponin C Mutations Differentially Affect Slow Skeletal and Cardiac Muscle Regulation

Frontiers in Physiology ◽

10.3389/fphys.2017.00221 ◽

2017 ◽

Vol 8 ◽

Cited By ~ 8

Author(s):

Tiago Veltri ◽

Maicon Landim-Vieira ◽

Michelle S. Parvatiyar ◽

David Gonzalez-Martinez ◽

Karissa M. Dieseldorff Jones ◽

...

Keyword(s):

Hypertrophic Cardiomyopathy ◽

Cardiac Muscle ◽

Cardiac Troponin ◽

Troponin C ◽

Muscle Regulation ◽

Cardiac Troponin C ◽

Cardiac Muscle Regulation

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Dynamic relations among length, tension, and intracellular Ca2+ in activated ferret papillary muscles

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1998.275.6.h1957 ◽

1998 ◽

Vol 275 (6) ◽

pp. H1957-H1962 ◽

Cited By ~ 1

Author(s):

Yasutake Saeki ◽

Satoshi Kurihara ◽

Kimiaki Komukai ◽

Tetsuya Ishikawa ◽

Kiyohiro Takigiku

Keyword(s):

Cardiac Troponin ◽

Muscle Length ◽

Length Change ◽

Troponin C ◽

Cardiac Troponin C ◽

Mechanical Constraints ◽

Tension Response ◽

Cardiac Muscles ◽

Length Changes ◽

Cross Bridges

To study the effects of mechanical constraints on the Ca2+ affinity of cardiac troponin C, we analyzed the tension and aequorin light (AL) responses to sinusoidal length changes (5–10% of the initial muscle length) in aequorin-injected, tetanized cardiac muscles. The amplitude of the quasi-sinusoidal tension and AL responses decreased with increasing length-perturbation frequency from 0.5 to 1 Hz at 24°C and from 1 to 3 Hz at 30°C. The increase in AL corresponded well to the decrease in tension; likewise, the decrease in AL to the increase in tension and the tension response lagged behind the length change. A further increase in frequency (>1 Hz at 24°C and >3 Hz at 30°C) markedly increased the amplitude of the tension responses but decreased the amplitude of the AL responses. The increase in AL lagged behind the decrease in tension; likewise, the decrease in AL lagged behind the increase in tension, and the tension response led the length change. From previous mechanistic interpretations of the frequency dependence of the amplitude of tension response, we argue that the Ca2+affinity of cardiac troponin C changes in parallel with the active tension (i.e., the number of active cross bridges) but not with the passive tension produced by the length perturbation-induced cross-bridge strain.

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Familial hypertrophic cardiomyopathy-related cardiac troponin C mutation L29Q affects Ca2+ binding and myofilament contractility

Physiological Genomics ◽

10.1152/physiolgenomics.00154.2007 ◽

2008 ◽

Vol 33 (2) ◽

pp. 257-266 ◽

Cited By ~ 38

Author(s):

Bo Liang ◽

Franca Chung ◽

Yang Qu ◽

Dmitri Pavlov ◽

Todd E. Gillis ◽

...

Keyword(s):

Hypertrophic Cardiomyopathy ◽

Cardiac Myocytes ◽

Cardiac Troponin ◽

Sarcomere Length ◽

Troponin C ◽

Familial Hypertrophic Cardiomyopathy ◽

Force Generation ◽

Binding Characteristics ◽

Cardiac Troponin C ◽

Myocyte Contractility

The cardiac troponin C (cTnC) mutation, L29Q, has been found in a patient with familial hypertrophic cardiomyopathy. We previously showed that L29, together with neighboring residues, Asp2, Val28, and Gly30, plays an important role in determining the Ca2+ affinity of site II, the regulatory site of mammalian cardiac troponin C (McTnC). Here we report on the Ca2+ binding characteristics of L29Q McTnC and D2N/V28I/L29Q/G30D McTnC (NIQD) utilizing the Phe27 → Trp (F27W) substitution, allowing one to monitor Ca2+ binding and release. We also studied the effect of these mutants on Ca2+ activation of force generation in single mouse cardiac myocytes using cTnC replacement, together with sarcomere length (SL) dependence. The Ca2+-binding affinity of site II of L29Q McTnCF27W and NIQD McTnCF27W was ∼1.3- and ∼1.9-fold higher, respectively, than that of McTnCF27W. The Ca2+ disassociation rate from site II of L29Q McTnCF27W and NIQD McTnCF27W was not significantly different than that of control (McTnCF27W). However, the rate of Ca2+ binding to site II was higher in L29Q McTnCF27W and NIQD McTnCF27W relative to control (∼1.5-fold and ∼2.0-fold respectively). The Ca2+ sensitivity of force generation was significantly higher in myocytes reconstituted with L29Q McTnC (∼1.4-fold) and NIQD McTnC (∼2-fold) compared with those reconstituted with McTnC. Interestingly, the change in Ca2+ sensitivity of force generation in response to an SL change (1.9, 2.1, and 2.3 μm) was significantly reduced in myocytes containing L29Q McTnC or NIQD McTnC. These results demonstrate that the L29Q mutation enhances the Ca2+-binding characteristics of cTnC and that when incorporated into cardiac myocytes, this mutant alters myocyte contractility.

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