Myosin MgADP release rate decreases at longer sarcomere length to prolong myosin attachment time in skinned rat myocardium

2015 ◽  
Vol 309 (12) ◽  
pp. H2087-H2097 ◽  
Author(s):  
Bertrand C. W. Tanner ◽  
Jason J. Breithaupt ◽  
Peter O. Awinda
Keyword(s):  
Release Rate ◽  
Thin Filament ◽  
Molecular Mechanisms ◽  
Sarcomere Length ◽  
Cardiac Contractility ◽  
Force Production ◽  
Cross Bridge ◽  
Thin Filament Proteins ◽  
Filament Activation ◽  
Ventricular Filling

Cardiac contractility increases as sarcomere length increases, suggesting that intrinsic molecular mechanisms underlie the Frank-Starling relationship to confer increased cardiac output with greater ventricular filling. The capacity of myosin to bind with actin and generate force in a muscle cell is Ca2+ regulated by thin-filament proteins and spatially regulated by sarcomere length as thick-to-thin filament overlap varies. One mechanism underlying greater cardiac contractility as sarcomere length increases could involve longer myosin attachment time ( t on) due to slowed myosin kinetics at longer sarcomere length. To test this idea, we used stochastic length-perturbation analysis in skinned rat papillary muscle strips to measure t on as [MgATP] varied (0.05–5 mM) at 1.9 and 2.2 μm sarcomere lengths. From this t on-MgATP relationship, we calculated cross-bridge MgADP release rate and MgATP binding rates. As MgATP increased, t on decreased for both sarcomere lengths, but t on was roughly 70% longer for 2.2 vs. 1.9 μm sarcomere length at maximally activated conditions. These t on differences were driven by a slower MgADP release rate at 2.2 μm sarcomere length (41 ± 3 vs. 74 ± 7 s−1), since MgATP binding rate was not different between the two sarcomere lengths. At submaximal activation levels near the pCa50 value of the tension-pCa relationship for each sarcomere length, length-dependent increases in t on were roughly 15% longer for 2.2 vs. 1.9 μm sarcomere length. These changes in cross-bridge kinetics could amplify cooperative cross-bridge contributions to force production and thin-filament activation at longer sarcomere length and suggest that length-dependent changes in myosin MgADP release rate may contribute to the Frank-Starling relationship in the heart.

scholarly journals Effect of Ca2+ binding properties of troponin C on rate of skeletal muscle force redevelopment

2010 ◽  
Vol 299 (5) ◽  
pp. C1091-C1099 ◽  
Author(s):  
Ryan S. Lee ◽  
Svetlana B. Tikunova ◽  
Kristopher P. Kline ◽  
Henry G. Zot ◽  
Javier E. Hasbun ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Muscle Force ◽  
Force Production ◽  
Dissociation Rate ◽  
Wild Type ◽  
Binding Properties ◽  
Cross Bridge ◽  
Skeletal Muscle Contraction ◽  
Filament Activation

To investigate effects of altering troponin (Tn)C Ca2+ binding properties on rate of skeletal muscle contraction, we generated three mutant TnCs with increased or decreased Ca2+ sensitivities. Ca2+ binding properties of the regulatory domain of TnC within the Tn complex were characterized by following the fluorescence of an IAANS probe attached onto the endogenous Cys99 residue of TnC. Compared with IAANS-labeled wild-type Tn complex, V43QTnC, T70DTnC, and I60QTnC exhibited ∼1.9-fold higher, ∼5.0-fold lower, and ∼52-fold lower Ca2+ sensitivity, respectively, and ∼3.6-fold slower, ∼5.7-fold faster, and ∼21-fold faster Ca2+ dissociation rate ( koff), respectively. On the basis of Kd and koff, these results suggest that the Ca2+ association rate to the Tn complex decreased ∼2-fold for I60QTnC and V43QTnC. Constructs were reconstituted into single-skinned rabbit psoas fibers to assess Ca2+ dependence of force development and rate of force redevelopment ( ktr) at 15°C, resulting in sensitization of both force and ktr to Ca2+ for V43QTnC, whereas T70DTnC and I60QTnC desensitized force and ktr to Ca2+, I60QTnC causing a greater desensitization. In addition, T70DTnC and I60QTnC depressed both maximal force (Fmax) and maximal ktr. Although V43QTnC and I60QTnC had drastically different effects on Ca2+ binding properties of TnC, they both exhibited decreases in cooperativity of force production and elevated ktr at force levels <30%Fmax vs. wild-type TnC. However, at matched force levels >30%Fmax ktr was similar for all TnC constructs. These results suggest that the TnC mutants primarily affected ktr through modulating the level of thin filament activation and not by altering intrinsic cross-bridge cycling properties. To corroborate this, NEM-S1, a non-force-generating cross-bridge analog that activates the thin filament, fully recovered maximal ktr for I60QTnC at low Ca2+ concentration. Thus TnC mutants with altered Ca2+ binding properties can control the rate of contraction by modulating thin filament activation without directly affecting intrinsic cross-bridge cycling rates.

scholarly journals Kinetics of a Ca(2+)-sensitive cross-bridge state transition in skeletal muscle fibers. Effects due to variations in thin filament activation by extraction of troponin C.

1991 ◽  
Vol 98 (2) ◽  
pp. 233-248 ◽  
Author(s):  
J M Metzger ◽  
R L Moss
Keyword(s):  
Steady State ◽  
Direct Effect ◽  
Thin Filament ◽  
Near Neighbor ◽  
Troponin C ◽  
Isometric Tension ◽  
Cross Bridge ◽  
Filament Activation ◽  
Kinetics Of ◽  
Partial Extraction

The rate constant of tension redevelopment (ktr; 1986. Proc. Natl. Acad. Sci. USA. 83:3542-3546) was determined at various levels of thin filament activation in skinned single fibers from mammalian fast twitch muscles. Activation was altered by (a) varying the concentration of free Ca2+ in the activating solution, or (b) extracting various amounts of troponin C (TnC) from whole troponin complexes while keeping the concentration of Ca2+ constant. TnC was extracted by bathing the fiber in a solution containing 5 mM EDTA, 10 mM HEPES, and 0.5 mM trifluoperazine dihydrochloride. Partial extraction of TnC resulted in a decrease in the Ca2+ sensitivity of isometric tension, presumably due to disruption of near-neighbor molecular cooperativity between functional groups (i.e., seven actin monomers plus associated troponin and tropomyosin) within the thin filament. Altering the level of thin filament activation by partial extraction of TnC while keeping Ca2+ concentration constant tested whether the Ca2+ sensitivity of ktr results from a direct effect of Ca2+ on cross-bridge state transitions or, alternatively, an indirect effect of Ca2+ on these transitions due to varying extents of thin filament activation. Results showed that the ktr-pCa relation was unaffected by partial extraction of TnC, while steady-state isometric tension exhibited the expected reduction in Ca2+ sensitivity. This finding provides evidence for a direct effect of Ca2+ on an apparent rate constant that limits the formation of force-bearing cross-bridge states in muscle fibers. Further, the kinetics of this transition are unaffected by disruption of near-neighbor thin filament cooperativity subsequent to extraction of TnC. Finally, the results support the idea that the steepness of the steady-state isometric tension-calcium relationship is at least in part due to mechanisms involving molecular cooperativity among thin filament regulatory proteins.

scholarly journals Nebulin Alters Cross-bridge Cycling Kinetics and Increases Thin Filament Activation

2009 ◽  
Vol 284 (45) ◽  
pp. 30889-30896 ◽  
Author(s):  
Murali Chandra ◽  
Ranganath Mamidi ◽  
Steven Ford ◽  
Carlos Hidalgo ◽  
Christian Witt ◽  
...  
Keyword(s):  
Thin Filament ◽  
Cross Bridge ◽  
Filament Activation

scholarly journals In Situ Time-Resolved FRET Reveals Effects of Sarcomere Length on Cardiac Thin-Filament Activation

2014 ◽  
Vol 107 (3) ◽  
pp. 682-693 ◽  
Author(s):  
King-Lun Li ◽  
Daniel Rieck ◽  
R. John Solaro ◽  
Wenji Dong
Keyword(s):  
Thin Filament ◽  
Sarcomere Length ◽  
Time Resolved ◽  
Filament Activation

scholarly journals Nebulin stiffens the thin filament and augments cross-bridge interaction in skeletal muscle

2018 ◽  
Vol 115 (41) ◽  
pp. 10369-10374 ◽  
Author(s):  
Balázs Kiss ◽  
Eun-Jeong Lee ◽  
Weikang Ma ◽  
Frank W. Li ◽  
Paola Tonino ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Thick Filament ◽  
Nemaline Myopathy ◽  
Sarcomeric Protein ◽  
Cross Bridge ◽  
Intact Muscle ◽  
Filament Activation ◽  
Muscle Thin Filament ◽  
And Function

Nebulin is a giant sarcomeric protein that spans along the actin filament in skeletal muscle, from the Z-disk to near the thin filament pointed end. Mutations in nebulin cause muscle weakness in nemaline myopathy patients, suggesting that nebulin plays important roles in force generation, yet little is known about nebulin’s influence on thin filament structure and function. Here, we used small-angle X-ray diffraction and compared intact muscle deficient in nebulin (using a conditional nebulin-knockout, Neb cKO) with control (Ctrl) muscle. When muscles were activated, the spacing of the actin subunit repeat (27 Å) increased in both genotypes; when converted to thin filament stiffness, the obtained value was 30 pN/nm in Ctrl muscle and 10 pN/nm in Neb cKO muscle; that is, the thin filament was approximately threefold stiffer when nebulin was present. In contrast, the thick filament stiffness was not different between the genotypes. A significantly shorter left-handed (59 Å) thin filament helical pitch was found in passive and contracting Neb cKO muscles, as well as impaired tropomyosin and troponin movement. Additionally, a reduced myosin mass transfer toward the thin filament in contracting Neb cKO muscle was found, suggesting reduced cross-bridge interaction. We conclude that nebulin is critically important for physiological force levels, as it greatly stiffens the skeletal muscle thin filament and contributes to thin filament activation and cross-bridge recruitment.

scholarly journals Inotropic interventions do not change the resting state of myosin motors during cardiac diastole

2018 ◽  
Vol 151 (1) ◽  
pp. 53-65 ◽  
Author(s):  
Marco Caremani ◽  
Francesca Pinzauti ◽  
Joseph D. Powers ◽  
Serena Governali ◽  
Theyencheri Narayanan ◽  
...  
Keyword(s):  
Protein C ◽  
Thin Filament ◽  
Sarcomere Length ◽  
Binding Protein ◽  
Thick Filament ◽  
Myosin Binding Protein ◽  
Myosin Binding Protein C ◽  
Filament Activation ◽  
Myosin Binding ◽  
Myosin Motors

When striated (skeletal and cardiac) muscle is in its relaxed state, myosin motors are packed in helical tracks on the surface of the thick filament, folded toward the center of the sarcomere, and unable to bind actin or hydrolyze ATP (OFF state). This raises the question of whatthe mechanism is that integrates the Ca2+-dependent thin filament activation, making myosin heads available for interaction with actin. Here we test the interdependency of the thin and thick filament regulatory mechanisms in intact trabeculae from the rat heart. We record the x-ray diffraction signals that mark the state of the thick filament during inotropic interventions (increase in sarcomere length from 1.95 to 2.25 µm and addition of 10−7 M isoprenaline), which potentiate the twitch force developed by an electrically paced trabecula by up to twofold. During diastole, none of the signals related to the OFF state of the thick filament are significantly affected by these interventions, except the intensity of both myosin-binding protein C– and troponin-related meridional reflections, which reduce by 20% in the presence of isoprenaline. These results indicate that recruitment of myosin motors from their OFF state occurs independently and downstream from thin filament activation. This is in agreement with the recently discovered mechanism based on thick filament mechanosensing in which the number of motors available for interaction with actin rapidly adapts to the stress on the thick filament and thus to the loading conditions of the contraction. The gain of this positive feedback may be modulated by both sarcomere length and the degree of phosphorylation of myosin-binding protein C.

scholarly journals Nebulin and titin modulate cross-bridge cycling and length-dependent calcium sensitivity

2019 ◽  
Vol 151 (5) ◽  
pp. 680-704 ◽  
Author(s):  
Srboljub M. Mijailovich ◽  
Boban Stojanovic ◽  
Djordje Nedic ◽  
Marina Svicevic ◽  
Michael A. Geeves ◽  
...  
Keyword(s):  
Muscle Function ◽  
Thin Filament ◽  
Structural Changes ◽  
Sarcomere Length ◽  
Muscle Force ◽  
Calcium Sensitivity ◽  
Filament Length ◽  
Simulation Code ◽  
Cross Bridge ◽  
Myosin Binding

Various mutations in the structural proteins nebulin and titin that are present in human disease are known to affect the contractility of striated muscle. Loss of nebulin is associated with reduced actin filament length and impairment of myosin binding to actin, whereas titin is thought to regulate muscle passive elasticity and is likely involved in length-dependent activation. Here, we sought to assess the modulation of muscle function by these sarcomeric proteins by using the computational platform muscle simulation code (MUSICO) to quantitatively separate the effects of structural changes, kinetics of cross-bridge cycling, and calcium sensitivity of the thin filaments. The simulations show that variation in thin filament length cannot by itself account for experimental observations of the contractility in nebulin-deficient muscle, but instead must be accompanied by a decreased myosin binding rate. Additionally, to match the observed calcium sensitivity, the rate of TnI detachment from actin needed to be increased. Simulations for cardiac muscle provided quantitative estimates of the effects of different titin-based passive elasticities on muscle force and activation in response to changes in sarcomere length and interfilament lattice spacing. Predicted force–pCa relations showed a decrease in both active tension and sensitivity to calcium with a decrease in passive tension and sarcomere length. We conclude that this behavior is caused by partial redistribution of the muscle load between active muscle force and titin-dependent passive force, and also by redistribution of stretch along the thin filament, which together modulate the release of TnI from actin. These data help advance understanding of how nebulin and titin mutations affect muscle function.

scholarly journals Comparison of putative cooperative mechanisms in cardiac muscle: length dependence and dynamic responses

1999 ◽  
Vol 276 (5) ◽  
pp. H1734-H1754 ◽  
Author(s):  
J. Jeremy Rice ◽  
Raimond L. Winslow ◽  
William C. Hunter
Keyword(s):  
Steady State ◽  
Thin Filament ◽  
Sarcomere Length ◽  
Isometric Force ◽  
Muscle Length ◽  
Dynamic Responses ◽  
Force Generation ◽  
Cross Bridge ◽  
Multiple Cross ◽  
Cross Bridges

Length-dependent steady-state and dynamic responses of five models of isometric force generation in cardiac myofilaments were compared with similar experimental data from the literature. The models were constructed by assuming different subsets of three putative cooperative mechanisms. Cooperative mechanism 1 holds that cross-bridge binding increases the affinity of troponin for Ca2+. In the models, cooperative mechanism 1can produce steep force-Ca2+(F-Ca) relations, but apparent cooperativity is highest at midlevel Ca2+ concentrations. During twitches, cooperative mechanism 1 has the effect of increasing latency to peak as the magnitude of force increases, an effect not seen experimentally. Cooperative mechanism 2 holds that the binding of a cross bridge increases the rate of formation of neighboring cross bridges and that multiple cross bridges can maintain activation of the thin filament in the absence of Ca2+. Only cooperative mechanism 2 can produce sarcomere length (SL)-dependent prolongation of twitches, but this mechanism has little effect on steady-state F-Ca relations. Cooperativity mechanism 3 is designed to simulate end-to-end interactions between adjacent troponin and tropomyosin. This mechanism can produce steep F-Ca relations with appropriate SL-dependent changes in Ca2+ sensitivity. With the assumption that tropomyosin shifting is faster than cross-bridge cycling, cooperative mechanism 3produces twitches where latency to peak is independent of the magnitude of force, as seen experimentally.

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