Troponin C modulates the activation of thin filaments by rigor cross-bridges

A relatively simple method is presented for incorporating cross-bridge mechanisms into a muscle model. The method is based on representing force in a half sarcomere as the product of the stiffness of all parallel cross bridges and their average distortion. Differential equations for sarcomeric stiffness are derived from a three-state kinetic scheme for the cross-bridge cycle. Differential equations for average distortion are derived from a distortional balance that accounts for distortion entering and leaving due to cross-bridge cycling and for distortion imposed by shearing motion between thick and thin filaments. The distortion equations are unique and enable sarcomere mechanodynamics to be described by only a few ordinary differential equations. Model predictions of small-amplitude step and sinusoidal responses agreed well with previously described experimental results and allowed unique interpretations to be made of various response components. Similarly good results were obtained for model reproductions of force-velocity and large-amplitude step and ramp responses. The model allowed reasonable predictions of contractile behavior by taking into account what is understood to be basic muscle contractile mechanisms.

Download Full-text

Functional and evolutionary relationships of troponin C

Physiological Genomics ◽

10.1152/physiolgenomics.00197.2007 ◽

2007 ◽

Vol 32 (1) ◽

pp. 16-27 ◽

Cited By ~ 34

Author(s):

Todd E. Gillis ◽

Christian R. Marshall ◽

Glen F. Tibbits

Keyword(s):

Functional Properties ◽

Thin Filament ◽

Troponin I ◽

Striated Muscle ◽

Troponin T ◽

Extensive Study ◽

Troponin C ◽

High Conservation ◽

Cross Bridges ◽

And Function

Striated muscle contraction is initiated when, following membrane depolarization, Ca2+ binds to the low-affinity Ca2+ binding sites of troponin C (TnC). The Ca2+ activation of this protein results in a rearrangement of the components (troponin I, troponin T, and tropomyosin) of the thin filament, resulting in increased interaction between actin and myosin and the formation of cross bridges. The functional properties of this protein are therefore critical in determining the active properties of striated muscle. To date there are 61 known TnCs that have been cloned from 41 vertebrate and invertebrate species. In vertebrate species there are also distinct fast skeletal muscle and cardiac TnC proteins. While there is relatively high conservation of the amino acid sequence of TnC homologs between species and tissue types, there is wide variation in the functional properties of these proteins. To date there has been extensive study of the structure and function of this protein and how differences in these translate into the functional properties of muscles. The purpose of this work is to integrate these studies of TnC with phylogenetic analysis to investigate how changes in the sequence and function of this protein, integrate with the evolution of striated muscle.

Download Full-text

Conformational Changes of Troponin C Within the Thin Filaments Detected by Neutron Scattering

Journal of Molecular Biology ◽

10.1016/j.jmb.2004.07.086 ◽

2004 ◽

Vol 342 (4) ◽

pp. 1209-1221 ◽

Cited By ~ 23

Author(s):

Fumiko Matsumoto ◽

Kouji Makino ◽

Kayo Maeda ◽

Heiko Patzelt ◽

Yuichiro Maéda ◽

...

Keyword(s):

Neutron Scattering ◽

Conformational Changes ◽

Troponin C ◽

Thin Filaments

Download Full-text

Activation Dependence of Stretch Activation in Mouse Skinned Myocardium: Implications for Ventricular Function

The Journal of General Physiology ◽

10.1085/jgp.200509432 ◽

2006 ◽

Vol 127 (2) ◽

pp. 95-107 ◽

Cited By ~ 62

Author(s):

Julian E. Stelzer ◽

Lars Larsson ◽

Daniel P. Fitzsimons ◽

Richard L. Moss

Keyword(s):

Isometric Force ◽

Force Characteristic ◽

Stretch Activation ◽

Thin Filaments ◽

Cross Bridge ◽

Steady Level ◽

Myocardial Stretch ◽

Myosin Subfragment 1 ◽

Activation Response ◽

Cross Bridges

Recent evidence suggests that ventricular ejection is partly powered by a delayed development of force, i.e., stretch activation, in regions of the ventricular wall due to stretch resulting from torsional twist of the ventricle around the apex-to-base axis. Given the potential importance of stretch activation in cardiac function, we characterized the stretch activation response and its Ca2+ dependence in murine skinned myocardium at 22°C in solutions of varying Ca2+ concentrations. Stretch activation was induced by suddenly imposing a stretch of 0.5–2.5% of initial length to the isometrically contracting muscle and then holding the muscle at the new length. The force response to stretch was multiphasic: force initially increased in proportion to the amount of stretch, reached a peak, and then declined to a minimum before redeveloping to a new steady level. This last phase of the response is the delayed force characteristic of myocardial stretch activation and is presumably due to increased attachment of cross-bridges as a consequence of stretch. The amplitude and rate of stretch activation varied with Ca2+ concentration and more specifically with the level of isometric force prior to the stretch. Since myocardial force is regulated both by Ca2+ binding to troponin-C and cross-bridge binding to thin filaments, we explored the role of cross-bridge binding in the stretch activation response using NEM-S1, a strong-binding, non-force–generating derivative of myosin subfragment 1. NEM-S1 treatment at submaximal Ca2+-activated isometric forces significantly accelerated the rate of the stretch activation response and reduced its amplitude. These data show that the rate and amplitude of myocardial stretch activation vary with the level of activation and that stretch activation involves cooperative binding of cross-bridges to the thin filament. Such a mechanism would contribute to increased systolic ejection in response to increased delivery of activator Ca2+ during excitation–contraction coupling.

Download Full-text

The off rate of Ca2+ from troponin C is regulated by force-generating cross bridges in skeletal muscle

Journal of Applied Physiology ◽

10.1152/japplphysiol.00376.2001 ◽

2002 ◽

Vol 92 (6) ◽

pp. 2409-2418 ◽

Cited By ~ 29

Author(s):

Ying Wang ◽

W. Glenn L. Kerrick

Keyword(s):

Skeletal Muscle ◽

Troponin C ◽

Transient Increase ◽

Skinned Fibers ◽

Mouse Skeletal Muscle ◽

Actomyosin Atpase ◽

Intact Muscle ◽

Intracellular Ca ◽

Cross Bridges ◽

Fenn Effect

The effects of dissociation of force-generating cross bridges on intracellular Ca2+, pCa-force, and pCa-ATPase relationships were investigated in mouse skeletal muscle. Mechanical length perturbations were used to dissociate force-generating cross bridges in either intact or skinned fibers. In intact muscle, an impulse stretch or release, a continuous length vibration, a nonoverlap stretch, or an unloaded shortening during a twitch caused a transient increase in intracellular Ca2+ compared with that in isometric controls and resulted in deactivation of the muscle. In skinned fibers, sinusoidal length vibrations shifted pCa-force and pCa-actomyosin ATPase rate relationships to higher Ca2+ concentrations and caused actomyosin ATPase rate to decrease at submaximal Ca2+ and increase at maximal Ca2+ activation. These results suggest that dissociation of force-generating cross bridges during a twitch causes the off rate of Ca2+ from troponin C to increase (a decrease in the Ca2+ affinity of troponin C), thus decreasing the Ca2+ sensitivity and resulting in the deactivation of the muscle. The results also suggest that the Fenn effect only exists at maximal but not submaximal force-activating Ca2+ concentrations.

Download Full-text

Troponin and Titin Coordinately Regulate Length-dependent Activation in Skinned Porcine Ventricular Muscle

The Journal of General Physiology ◽

10.1085/jgp.200709895 ◽

2008 ◽

Vol 131 (3) ◽

pp. 275-283 ◽

Cited By ~ 38

Author(s):

Takako Terui ◽

Munguntsetseg Sodnomtseren ◽

Douchi Matsuba ◽

Jun Udaka ◽

Shin'ichi Ishiwata ◽

...

Keyword(s):

Skeletal Muscle ◽

Thin Filament ◽

Left Ventricular ◽

Ventricular Muscle ◽

Passive Force ◽

Active Force ◽

Fast Skeletal Muscle ◽

Thin Filaments ◽

Cross Bridges ◽

Length Dependent Activation

We investigated the molecular mechanism by which troponin (Tn) regulates the Frank-Starling mechanism of the heart. Quasi-complete reconstitution of thin filaments with rabbit fast skeletal Tn (sTn) attenuated length-dependent activation in skinned porcine left ventricular muscle, to a magnitude similar to that observed in rabbit fast skeletal muscle. The rate of force redevelopment increased upon sTn reconstitution at submaximal levels, coupled with an increase in Ca2+ sensitivity of force, suggesting the acceleration of cross-bridge formation and, accordingly, a reduction in the fraction of resting cross-bridges that can potentially produce additional active force. An increase in titin-based passive force, induced by manipulating the prehistory of stretch, enhanced length-dependent activation, in both control and sTn-reconstituted muscles. Furthermore, reconstitution of rabbit fast skeletal muscle with porcine left ventricular Tn enhanced length-dependent activation, accompanied by a decrease in Ca2+ sensitivity of force. These findings demonstrate that Tn plays an important role in the Frank-Starling mechanism of the heart via on–off switching of the thin filament state, in concert with titin-based regulation.

Download Full-text

Polarization of Tryptophan Fluorescence from Single Striated Muscle Fibers

The Journal of General Physiology ◽

10.1085/jgp.59.1.103 ◽

1972 ◽

Vol 59 (1) ◽

pp. 103-120 ◽

Cited By ~ 82

Author(s):

C. G. dos Remedios ◽

R. G. C. Millikan ◽

M. F. Morales

Keyword(s):

Sarcomere Length ◽

Striated Muscle ◽

Muscle Fibers ◽

Tryptophan Fluorescence ◽

Thin Filaments ◽

A Value ◽

Striated Muscle Fibers ◽

Types Of Muscle Fibers ◽

Cross Bridges ◽

Contraction And Relaxation

Instrumentation has been developed to detect rapidly the polarization of tryptophan fluorescence from single muscle fibers in rigor, relaxation, and contraction. The polarization parameter (P⊥) obtained by exiciting the muscle tryptophans with light polarized perpendicular to the long axis of the muscle fiber had a magnitude P⊥ (relaxation) > P⊥ (contraction) > P⊥ (rigor) for the three types of muscle fibers examined (glycerinated rabbit psoas, glycerinated dorsal longitudinal flight muscle of Lethocerus americanus, and live semitendinosus of Rana pipiens). P⊥ from single psoas fibers in rigor was found to increase as the sarcomere length increased but in relaxed fibers P⊥ was independent of sarcomere length. After rigor, pyrophosphate produced little or no change in P⊥, but following an adenosine triphosphate (ATP)-containing solution, pyrophosphate produced a value of P⊥ that fell between the contraction and relaxation values. Sinusoidal or square wave oscillations of the muscle of amplitude 0.5–2.0% of the sarcomere length and frequency 1, 2, or 5 Hz were applied in rigor when the myosin cross-bridges are considered to be firmly attached to the thin filaments. No significant changes in P⊥ were observed in either rigor or relaxation. The preceding results together with our present knowledge of tryptophan distribution in the contractile proteins has led us to the conclusion that the parameter P⊥ is a probe of the contractile state of myosin which is probably sensitive to the orientation of the myosin S1 subfragment.

Download Full-text

Analysis of myofibrillar structure and assembly using fluorescently labeled contractile proteins.

The Journal of Cell Biology ◽

10.1083/jcb.98.3.825 ◽

1984 ◽

Vol 98 (3) ◽

pp. 825-833 ◽

Cited By ~ 65

Author(s):

J W Sanger ◽

B Mittal ◽

J M Sanger

Keyword(s):

Actin Filaments ◽

Striated Muscle ◽

Contractile Proteins ◽

Actin Binding ◽

Thin Filaments ◽

In Vitro System ◽

Self Association ◽

Cross Bridges

To study how contractile proteins become organized into sarcomeric units in striated muscle, we have exposed glycerinated myofibrils to fluorescently labeled actin, alpha-actinin, and tropomyosin. In this in vitro system, alpha-actinin bound to the Z-bands and the binding could not be saturated by prior addition of excess unlabeled alpha-actinin. Conditions known to prevent self-association of alpha-actinin, however, blocked the binding of fluorescently labeled alpha-actinin to Z-bands. When tropomyosin was removed from the myofibrils, alpha-actinin then added to the thin filaments as well as the Z-bands. Actin bound in a doublet pattern to the regions of the myosin filaments where there were free cross-bridges i.e., in that part of the A-band free of interdigitating native thin filaments but not in the center of the A-band which lacks cross-bridges. In the presence of 0.1-0.2 mM ATP, no actin binding occurred. When unlabeled alpha-actinin was added first to myofibrils and then labeled actin was added fluorescence occurred not in a doublet pattern but along the entire length of the myofibril. Tropomyosin did not bind to myofibrils unless the existing tropomyosin was first removed, in which case it added to the thin filaments in the l-band. Tropomyosin did bind, however, to the exogenously added tropomyosin-free actin that localizes as a doublet in the A-band. These results indicate that the alpha-actinin present in Z-bands of myofibrils is fully complexed with actin, but can bind exogenous alpha-actinin and, if actin is added subsequently, the exogenous alpha-actinin in the Z-band will bind the newly formed fluorescent actin filaments. Myofibrillar actin filaments did not increase in length when G-actin was present under polymerizing conditions, nor did they bind any added tropomyosin. These observations are discussed in terms of the structure and in vivo assembly of myofibrils.

Download Full-text

Looking for Targets to Restore the Contractile Function in Congenital Myopathy Caused by Gln147Pro Tropomyosin

International Journal of Molecular Sciences ◽

10.3390/ijms21207590 ◽

2020 ◽

Vol 21 (20) ◽

pp. 7590

Author(s):

Olga E. Karpicheva ◽

Armen O. Simonyan ◽

Nikita A. Rysev ◽

Charles S. Redwood ◽

Yurii S. Borovikov

Keyword(s):

Atp Hydrolysis ◽

Contractile Function ◽

Congenital Myopathy ◽

Muscle Disease ◽

Fluorescence Probes ◽

Single Muscle ◽

Angular Orientation ◽

Thin Filaments ◽

Cross Bridges ◽

Insight Into

We have used the technique of polarized microfluorimetry to obtain new insight into the pathogenesis of skeletal muscle disease caused by the Gln147Pro substitution in β-tropomyosin (Tpm2.2). The spatial rearrangements of actin, myosin and tropomyosin in the single muscle fiber containing reconstituted thin filaments were studied during simulation of several stages of ATP hydrolysis cycle. The angular orientation of the fluorescence probes bound to tropomyosin was found to be changed by the substitution and was characteristic for a shift of tropomyosin strands closer to the inner actin domains. It was observed both in the absence and in the presence of troponin, Ca2+ and myosin heads at all simulated stages of the ATPase cycle. The mutant showed higher flexibility. Moreover, the Gln147Pro substitution disrupted the myosin-induced displacement of tropomyosin over actin. The irregular positioning of the mutant tropomyosin caused premature activation of actin monomers and a tendency to increase the number of myosin cross-bridges in a state of strong binding with actin at low Ca2+.

Download Full-text