scholarly journals Acceleration of Stretch Activation in Murine Myocardium due to Phosphorylation of Myosin Regulatory Light Chain

2006 ◽  
Vol 128 (3) ◽  
pp. 261-272 ◽  
Author(s):  
Julian E. Stelzer ◽  
Jitandrakumar R. Patel ◽  
Richard L. Moss
Keyword(s):  
Light Chain ◽  
Isometric Force ◽  
Systolic Function ◽  
Muscle Length ◽  
Striated Muscles ◽  
Stretch Activation ◽  
Force Transmission ◽  
Force Development ◽  
Cross Bridge ◽  
Kinetics Of

The regulatory light chains (RLCs) of vertebrate muscle myosins bind to the neck region of the heavy chain domain and are thought to play important structural roles in force transmission between the cross-bridge head and thick filament backbone. In vertebrate striated muscles, the RLCs are reversibly phosphorylated by a specific myosin light chain kinase (MLCK), and while phosphorylation has been shown to accelerate the kinetics of force development in skeletal muscle, the effects of RLC phosphorylation in cardiac muscle are not well understood. Here, we assessed the effects of RLC phosphorylation on force, and the kinetics of force development in myocardium was isolated in the presence of 2,3-butanedione monoxime (BDM) to dephosphorylate RLC, subsequently skinned, and then treated with MLCK to phosphorylate RLC. Since RLC phosphorylation may be an important determinant of stretch activation in myocardium, we recorded the force responses of skinned myocardium to sudden stretches of 1% of muscle length both before and after treatment with MLCK. MLCK increased RLC phosphorylation, increased the Ca2+ sensitivity of isometric force, reduced the steepness of the force–pCa relationship, and increased both Ca2+-activated and Ca2+-independent force. Sudden stretch of myocardium during an otherwise isometric contraction resulted in a concomitant increase in force that quickly decayed to a minimum and was followed by a delayed redevelopment of force, i.e., stretch activation, to levels greater than pre-stretch force. MLCK had profound effects on the stretch activation responses during maximal and submaximal activations: the amplitude and rate of force decay after stretch were significantly reduced, and the rate of delayed force recovery was accelerated and its amplitude reduced. These data show that RLC phosphorylation increases force and the rate of cross-bridge recruitment in murine myocardium, which would increase power generation in vivo and thereby enhance systolic function.

The Frank-Starling mechanism is not mediated by changes in rate of cross-bridge detachment

1997 ◽  
Vol 273 (5) ◽  
pp. H2428-H2435 ◽  
Author(s):  
Thomas Wannenburg ◽  
Paul M. L. Janssen ◽  
Dongsheng Fan ◽  
Pieter P. De Tombe
Keyword(s):  
Cardiac Muscle ◽  
Maximum Rate ◽  
Sarcomere Length ◽  
Myosin Head ◽  
Isometric Force ◽  
Force Development ◽  
Cross Bridge ◽  
Average Slope ◽  
The Cross ◽  
Kinetics Of

We tested the hypothesis that the Frank-Starling relationship is mediated by changes in the rate of cross-bridge detachment in cardiac muscle. We simultaneously measured isometric force development and the rate of ATP consumption at various levels of Ca2+ activation in skinned rat cardiac trabecular muscles at three sarcomere lengths (2.0, 2.1, and 2.2 μm). The maximum rate of ATP consumption was 1.5 nmol ⋅ s−1 ⋅ μl fiber vol−1, which represents an estimated adenosinetriphosphatase (ATPase) rate of ∼10 s−1 per myosin head at 24°C. The rate of ATP consumption was tightly and linearly coupled to the level of isometric force development, and changes in sarcomere length had no effect on the slope of the force-ATPase relationships. The average slope of the force-ATPase relationships was 15.5 pmol ⋅ mN−1 ⋅ mm−1. These results suggest that the mechanisms that underlie the Frank-Starling relationship in cardiac muscle do not involve changes in the kinetics of the apparent detachment step in the cross-bridge cycle.

Basal myosin light chain phosphorylation is a determinant of Ca2+ sensitivity of force and activation dependence of the kinetics of myocardial force development

2004 ◽  
Vol 287 (6) ◽  
pp. H2712-H2718 ◽  
Author(s):  
M. Charlotte Olsson ◽  
Jitandrakumar R. Patel ◽  
Daniel P. Fitzsimons ◽  
Jeffery W. Walker ◽  
Richard L. Moss
Keyword(s):  
Light Chain ◽  
Myosin Light Chain ◽  
Isometric Force ◽  
Regulatory Light Chains ◽  
Force Development ◽  
Interaction Kinetics ◽  
Functional Consequences ◽  
Butanedione Monoxime ◽  
Kinetics Of ◽  
Activation Dependence

It is generally recognized that ventricular myosin regulatory light chains (RLC) are ∼40% phosphorylated under basal conditions, and there is little change in RLC phosphorylation with agonist stimulation of myocardium or altered stimulation frequency. To establish the functional consequences of basal RLC phosphorylation in the heart, we measured mechanical properties of rat skinned trabeculae in which ∼7% or ∼58% of total RLC was phosphorylated. The protocol for achieving ∼7% phosphorylation of RLC involved isolating trabeculae in the presence of 2,3-butanedione monoxime (BDM) to dephosphorylate RLC from its baseline level. Subsequent phosphorylation to ∼58% of total was achieved by incubating BDM-treated trabeculae in solution containing smooth muscle myosin light chain kinase, calmodulin, and Ca2+ (i.e., MLCK treatment). After MLCK treatment, Ca2+ sensitivity of force increased by 0.06 pCa units and maximum force increased by 5%. The rate constant of force development ( ktr) increased as a function of Ca2+ concentration in the range between pCa 5.8 and pCa 4.5. When expressed versus pCa, the activation dependence of ktr appeared to be unaffected by MLCK treatment; however, when activation was expressed in terms of isometric force-generating capability (as a fraction of maximum), MLCK treatment slowed ktr at submaximal activations. These results suggest that basal phosphorylation of RLC plays a role in setting the kinetics of force development and Ca2+ sensitivity of force in cardiac muscle. Our results also argue that changes in RLC phosphorylation in the range examined here influence actin-myosin interaction kinetics differently in heart muscle than was previously reported for skeletal muscle.

scholarly journals Characterization of cross-bridge elasticity and kinetics of cross-bridge cycling during force development in single smooth muscle cells.

1988 ◽  
Vol 91 (6) ◽  
pp. 761-779 ◽  
Author(s):  
D M Warshaw ◽  
D D Rees ◽  
F S Fay
Keyword(s):  
Skeletal Muscle ◽  
Smooth Muscle ◽  
Isometric Force ◽  
Force Development ◽  
Cross Bridge ◽  
Tension Recovery ◽  
Length Changes ◽  
Cross Bridges ◽  
Initial Force ◽  
Kinetics Of

Force development in smooth muscle, as in skeletal muscle, is believed to reflect recruitment of force-generating myosin cross-bridges. However, little is known about the events underlying cross-bridge recruitment as the muscle cell approaches peak isometric force and then enters a period of tension maintenance. In the present studies on single smooth muscle cells isolated from the toad (Bufo marinus) stomach muscularis, active muscle stiffness, calculated from the force response to small sinusoidal length changes (0.5% cell length, 250 Hz), was utilized to estimate the relative number of attached cross-bridges. By comparing stiffness during initial force development to stiffness during force redevelopment immediately after a quick release imposed at peak force, we propose that the instantaneous active stiffness of the cell reflects both a linearly elastic cross-bridge element having 1.5 times the compliance of the cross-bridge in frog skeletal muscle and a series elastic component having an exponential length-force relationship. At the onset of force development, the ratio of stiffness to force was 2.5 times greater than at peak isometric force. These data suggest that, upon activation, cross-bridges attach in at least two states (i.e., low-force-producing and high-force-producing) and redistribute to a steady state distribution at peak isometric force. The possibility that the cross-bridge cycling rate was modulated with time was also investigated by analyzing the time course of tension recovery to small, rapid step length changes (0.5% cell length in 2.5 ms) imposed during initial force development, at peak force, and after 15 s of tension maintenance. The rate of tension recovery slowed continuously throughout force development following activation and slowed further as force was maintained. Our results suggest that the kinetics of force production in smooth muscle may involve a redistribution of cross-bridge populations between two attached states and that the average cycling rate of these cross-bridges becomes slower with time during contraction.

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

2006 ◽  
Vol 127 (2) ◽  
pp. 95-107 ◽  
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.

scholarly journals Mavacamten Decreases Maximal Force and Ca2+-sensitivity in the N47K-Myosin Regulatory Light Chain Mouse Model of Hypertrophic Cardiomyopathy

2020 ◽  
Author(s):  
Peter O Awinda ◽  
Marissa Watanabe ◽  
Yemeserach M. Bishaw ◽  
Anna M Huckabee ◽  
Keinan B Agonias ◽  
...  
Keyword(s):  
Heart Disease ◽  
Hypertrophic Cardiomyopathy ◽  
Light Chain ◽  
Isometric Force ◽  
Regulatory Light Chain ◽  
Isometric Tension ◽  
Myosin Regulatory Light Chain ◽  
Cardiac Myosin ◽  
Cross Bridge ◽  
Obstructive Hypertrophic Cardiomyopathy

Morbidity and mortality associated with heart disease is a growing threat to the global population and novel therapies are needed. Mavacamten (formerly called MYK-461) is a small molecule that binds to cardiac myosin and inhibits myosin ATPase. Mavacamten is currently in clinical trials for the treatment of obstructive hypertrophic cardiomyopathy (HCM), and it may provide benefits for treating other forms of heart disease. We investigated the effect of mavacamten on cardiac muscle contraction in two transgenic mouse lines expressing the human isoform of cardiac myosin regulatory light chain (RLC) in their hearts. Control mice expressed wild-type RLC (WT-RLC), and HCM mice expressed the N47K RLC mutation. In the absence of mavacamten, skinned papillary muscle strips from WT-RLC mice produced greater isometric force than strips from N47K mice. Adding 0.3 µM mavacamten decreased maximal isometric force and reduced Ca2+-sensitivity of contraction for both genotypes, but this reduction in pCa50 was nearly twice as large for WT-RLC vs. N47K. We also used stochastic length-perturbation analysis to characterize cross-bridge kinetics. The cross-bridge detachment rate was measured as a function of [MgATP] to determine the effect of mavacamten on myosin nucleotide handling rates. Mavacamten increased the MgADP release and MgATP binding rates for both genotypes, thereby contributing to faster cross-bridge detachment, which could speed myocardial relaxation during diastole. Our data suggest that mavacamten reduces isometric tension and Ca2+-sensitivity of contraction via decreased strong cross-bridge binding. Mavacamten may become a useful therapy for patients with heart disease, including some forms of HCM.

scholarly journals A common mechanism for concurrent changes of diastolic muscle length and systolic function in intact hearts

2001 ◽  
Vol 280 (4) ◽  
pp. H1513-H1518 ◽  
Author(s):  
Li Lu ◽  
Ya Xu ◽  
Peili Zhu ◽  
Clifford Greyson ◽  
Gregory G. Schwartz
Keyword(s):  
Diastolic Pressure ◽  
Systolic Function ◽  
Muscle Length ◽  
Left Ventricular ◽  
Segment Length ◽  
Common Mechanism ◽  
External Work ◽  
Cross Bridge ◽  
Cross Bridges

Mechanical properties of the myocardium at end diastole have been thought to be dominated by passive material properties rather than by active sarcomere cross-bridge interactions. This study tested the hypothesis that residual cross-bridges significantly contribute to end-diastolic mechanics in vivo and that changes in end-diastolic cross-bridge interaction parallel concurrent changes in systolic cross-bridge interaction. Open-chest anesthetized pigs were treated with intracoronary verapamil ( n = 7) or 2,3-butanedione monoxime (BDM; n = 8). Regional left ventricular external work and end-diastolic pressure (EDP) versus end-diastolic segment length (EDL) relations were determined in the treated and untreated regions of each heart. Both agents reduced external work of treated regions to 31–38% of baseline and concurrently shifted EDP versus EDL relations to the right (i.e., greater EDL at a given EDP) by an average of 5% ( P < 0.05). During washout of the drugs, EDP versus EDL returned to baseline in parallel with recovery of external work. Sarcomere length, measured by transmission electron microscopy in BDM-treated and untreated regions of the same hearts after diastolic arrest and perfusion fixation, was 8% greater in BDM-treated regions ( P < 0.01). We concluded that residual diastolic cross-bridges significantly and reversibly influence end-diastolic mechanics in vivo. Alterations of end-diastolic and systolic cross-bridge interactions occur in parallel.

scholarly journals 2-Deoxyadenosine triphosphate restores the contractile function of cardiac myofibril from adult dogs with naturally occurring dilated cardiomyopathy

2016 ◽  
Vol 310 (1) ◽  
pp. H80-H91 ◽  
Author(s):  
Yuanhua Cheng ◽  
Kaley A. Hogarth ◽  
M. Lynne O'Sullivan ◽  
Michael Regnier ◽  
W. Glen Pyle
Keyword(s):  
Dilated Cardiomyopathy ◽  
Contractile Function ◽  
Systolic Function ◽  
Major Type ◽  
Slow Phase ◽  
Phase Relaxation ◽  
Cross Bridge ◽  
Naturally Occurring ◽  
Deoxyadenosine Triphosphate ◽  
Kinetics Of

Dilated cardiomyopathy (DCM) is a major type of heart failure resulting from loss of systolic function. Naturally occurring canine DCM is a widely accepted experimental paradigm for studying human DCM. 2-Deoxyadenosine triphosphate (dATP) can be used by myosin and is a superior energy substrate over ATP for cross-bridge formation and increased systolic function. The objective of this study was to evaluate the beneficial effect of dATP on contractile function of cardiac myofibrils from dogs with naturally occurring DCM. We measured actomyosin NTPase activity and contraction/relaxation properties of isolated myofibrils from nonfailing (NF) and DCM canine hearts. NTPase assays indicated replacement of ATP with dATP significantly increased myofilament activity in both NF and DCM samples. dATP significantly improved maximal tension of DCM myofibrils to the NF sample level. dATP also restored Ca2+ sensitivity of tension that was reduced in DCM samples. Similarly, dATP increased the kinetics of contractile activation (kACT), with no impact on the rate of cross-bridge tension redevelopment (kTR). Thus, the activation kinetics (kACT/kTR) that were reduced in DCM samples were restored for dATP to NF sample levels. dATP had little effect on relaxation. The rate of early slow-phase relaxation was slightly reduced with dATP, but its duration was not, nor was the fast-phase relaxation or times to 50 and 90% relaxation. Our findings suggest that myosin utilization of dATP improves cardiac myofibril contractile properties of naturally occurring DCM canine samples, restoring them to NF levels, without compromising relaxation. This suggests elevation of cardiac dATP is a promising approach for the treatment of DCM.

scholarly journals Cooperative Mechanisms in the Activation Dependence of the Rate of Force Development in Rabbit Skinned Skeletal Muscle Fibers

2001 ◽  
Vol 117 (2) ◽  
pp. 133-148 ◽  
Author(s):  
Daniel P. Fitzsimons ◽  
Jitandrakumar R. Patel ◽  
Kenneth S. Campbell ◽  
Richard L. Moss
Keyword(s):  
Skeletal Muscle ◽  
Force Development ◽  
Cross Bridge ◽  
Strong Binding ◽  
Regulation Of Contraction ◽  
Cooperative Process ◽  
Cross Bridges ◽  
Kinetics Of ◽  
Partial Extraction ◽  
Activation Dependence

Regulation of contraction in skeletal muscle is a highly cooperative process involving Ca2+ binding to troponin C (TnC) and strong binding of myosin cross-bridges to actin. To further investigate the role(s) of cooperation in activating the kinetics of cross-bridge cycling, we measured the Ca2+ dependence of the rate constant of force redevelopment (ktr) in skinned single fibers in which cross-bridge and Ca2+ binding were also perturbed. Ca2+ sensitivity of tension, the steepness of the force-pCa relationship, and Ca2+ dependence of ktr were measured in skinned fibers that were (1) treated with NEM-S1, a strong-binding, non–force-generating derivative of myosin subfragment 1, to promote cooperative strong binding of endogenous cross-bridges to actin; (2) subjected to partial extraction of TnC to disrupt the spread of activation along the thin filament; or (3) both, partial extraction of TnC and treatment with NEM-S1. The steepness of the force-pCa relationship was consistently reduced by treatment with NEM-S1, by partial extraction of TnC, or by a combination of TnC extraction and NEM-S1, indicating a decrease in the apparent cooperativity of activation. Partial extraction of TnC or NEM-S1 treatment accelerated the rate of force redevelopment at each submaximal force, but had no effect on kinetics of force development in maximally activated preparations. At low levels of Ca2+, 3 μM NEM-S1 increased ktr to maximal values, and higher concentrations of NEM-S1 (6 or 10 μM) increased ktr to greater than maximal values. NEM-S1 also accelerated ktr at intermediate levels of activation, but to values that were submaximal. However, the combination of partial TnC extraction and 6 μM NEM-S1 increased ktr to virtually identical supramaximal values at all levels of activation, thus, completely eliminating the activation dependence of ktr. These results show that ktr is not maximal in control fibers, even at saturating [Ca2+], and suggest that activation dependence of ktr is due to the combined activating effects of Ca2+ binding to TnC and cross-bridge binding to actin.

scholarly journals A myosin-based mechanism for stretch activation and its possible role revealed by varying phosphate concentration in fast and slow mouse skeletal muscle fibers

2019 ◽  
Vol 317 (6) ◽  
pp. C1143-C1152 ◽  
Author(s):  
Chad R. Straight ◽  
Kaylyn M. Bell ◽  
Jared N. Slosberg ◽  
Mark S. Miller ◽  
Douglas M. Swank
Keyword(s):  
Skeletal Muscle ◽  
Isometric Force ◽  
Muscle Fibers ◽  
Muscle Length ◽  
Power Stroke ◽  
Mammalian Skeletal Muscle ◽  
Stretch Activation ◽  
Force Ratio ◽  
Slow Twitch ◽  
Fast Twitch

Stretch activation (SA) is a delayed increase in force following a rapid muscle length increase. SA is best known for its role in asynchronous insect flight muscle, where it has replaced calcium’s typical role of modulating muscle force levels during a contraction cycle. SA also occurs in mammalian skeletal muscle but has previously been thought to be too low in magnitude, relative to calcium-activated (CA) force, to be a significant contributor to force generation during locomotion. To test this supposition, we compared SA and CA force at different Pi concentrations (0–16 mM) in skinned mouse soleus (slow-twitch) and extensor digitorum longus (EDL; fast-twitch) muscle fibers. CA isometric force decreased similarly in both muscles with increasing Pi, as expected. SA force decreased with Pi in EDL (40%), leaving the SA to CA force ratio relatively constant across Pi concentrations (17–25%). In contrast, SA force increased in soleus (42%), causing a quadrupling of the SA to CA force ratio, from 11% at 0 mM Pi to 43% at 16 mM Pi, showing that SA is a significant force modulator in slow-twitch mammalian fibers. This modulation would be most prominent during prolonged muscle use, which increases Pi concentration and impairs calcium cycling. Based upon our previous Drosophila myosin isoform studies and this work, we propose that in slow-twitch fibers a rapid stretch in the presence of Pi reverses myosin’s power stroke, enabling quick rebinding to actin and enhanced force production, while in fast-twitch fibers, stretch and Pi cause myosin to detach from actin.

scholarly journals Current Understanding of Residual Force Enhancement: Cross-Bridge Component and Non-Cross-Bridge Component

2019 ◽  
Vol 20 (21) ◽  
pp. 5479 ◽  
Author(s):  
Atsuki Fukutani ◽  
Walter Herzog
Keyword(s):  
Isometric Force ◽  
Muscle Length ◽  
Eccentric Contraction ◽  
Force Enhancement ◽  
Mechanical Responses ◽  
Cross Bridge ◽  
Myosin Filaments ◽  
Residual Force ◽  
Residual Force Enhancement ◽  
The Cross

Muscle contraction is initiated by the interaction between actin and myosin filaments. The sliding of actin filaments relative to myosin filaments is produced by cross-bridge cycling, which is governed by the theoretical framework of the cross-bridge theory. The cross-bridge theory explains well a number of mechanical responses, such as isometric and concentric contractions. However, some experimental observations cannot be explained with the cross-bridge theory; for example, the increased isometric force after eccentric contractions. The steady-state, isometric force after an eccentric contraction is greater than that attained in a purely isometric contraction at the same muscle length and same activation level. This well-acknowledged and universally observed property is referred to as residual force enhancement (rFE). Since rFE cannot be explained by the cross-bridge theory, alternative mechanisms for explaining this force response have been proposed. In this review, we introduce the basic concepts of sarcomere length non-uniformity and titin elasticity, which are the primary candidates that have been used for explaining rFE, and discuss unresolved problems regarding these mechanisms, and how to proceed with future experiments in this exciting area of research.

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