More roles for the (passive) giant. Focus on “The increase in non-cross-bridge forces after stretch of activated striated muscle is related to titin isoforms”

Skeletal muscles present a non-cross-bridge increase in sarcomere stiffness and tension on Ca2+ activation, referred to as static stiffness and static tension, respectively. It has been hypothesized that this increase in tension is caused by Ca2+-dependent changes in the properties of titin molecules. To verify this hypothesis, we investigated the static tension in muscles containing different titin isoforms. Permeabilized myofibrils were isolated from the psoas, soleus, and heart ventricle from the rabbit, and tested in pCa 9.0 and pCa 4.5, before and after extraction of troponin C, thin filaments, and treatment with the actomyosin inhibitor blebbistatin. The myofibrils were tested with stretches of different amplitudes in sarcomere lengths varying between 1.93 and 3.37 μm for the psoas, 2.68 and 4.21 μm for the soleus, and 1.51 and 2.86 μm for the ventricle. Using gel electrophoresis, we confirmed that the three muscles tested have different titin isoforms. The static tension was present in psoas and soleus myofibrils, but not in ventricle myofibrils, and higher in psoas myofibrils than in soleus myofibrils. These results suggest that the increase in the static tension is directly associated with Ca2+-dependent change in titin properties and not associated with changes in titin-actin interactions.

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Phosphate has dual roles in cross-bridge kinetics in rabbit psoas single myofibrils

The Journal of General Physiology ◽

10.1085/jgp.202012755 ◽

2021 ◽

Vol 153 (3) ◽

Cited By ~ 1

Author(s):

Masataka Kawai ◽

Robert Stehle ◽

Gabriele Pfitzer ◽

Bogdan Iorga

Keyword(s):

Rate Constants ◽

Striated Muscle ◽

Intrinsic Rate ◽

Isometric Tension ◽

Force Generation ◽

Skinned Fibers ◽

Sinusoidal Analysis ◽

Rabbit Psoas ◽

Cross Bridge

In this study, we aimed to study the role of inorganic phosphate (Pi) in the production of oscillatory work and cross-bridge (CB) kinetics of striated muscle. We applied small-amplitude sinusoidal length oscillations to rabbit psoas single myofibrils and muscle fibers, and the resulting force responses were analyzed during maximal Ca2+ activation (pCa 4.65) at 15°C. Three exponential processes, A, B, and C, were identified from the tension transients, which were studied as functions of Pi concentration ([Pi]). In myofibrils, we found that process C, corresponding to phase 2 of step analysis during isometric contraction, is almost a perfect single exponential function compared with skinned fibers, which exhibit distributed rate constants, as described previously. The [Pi] dependence of the apparent rate constants 2πb and 2πc, and that of isometric tension, was studied to characterize the force generation and Pi release steps in the CB cycle, as well as the inhibitory effect of Pi. In contrast to skinned fibers, Pi does not accumulate in the core of myofibrils, allowing sinusoidal analysis to be performed nearly at [Pi] = 0. Process B disappeared as [Pi] approached 0 mM in myofibrils, indicating the significance of the role of Pi rebinding to CBs in the production of oscillatory work (process B). Our results also suggest that Pi competitively inhibits ATP binding to CBs, with an inhibitory dissociation constant of ∼2.6 mM. Finally, we found that the sinusoidal waveform of tension is mostly distorted by second harmonics and that this distortion is closely correlated with production of oscillatory work, indicating that the mechanism of generating force is intrinsically nonlinear. A nonlinear force generation mechanism suggests that the length-dependent intrinsic rate constant is asymmetric upon stretch and release and that there may be a ratchet mechanism involved in the CB cycle.

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The effects of deuterium oxide on the active cross-bridge motion of thick filaments isolated from striated muscle of Limulus

Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology ◽

10.1016/0167-4838(85)90291-2 ◽

1985 ◽

Vol 830 (3) ◽

pp. 333-336 ◽

Cited By ~ 2

Author(s):

Shih-Fang Fan ◽

M.M. Dewey ◽

D. Colflesh ◽

B. Chu

Keyword(s):

Striated Muscle ◽

Deuterium Oxide ◽

Cross Bridge ◽

Thick Filaments

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The latch-bridge hypothesis of smooth muscle contraction

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y05-090 ◽

2005 ◽

Vol 83 (10) ◽

pp. 857-864 ◽

Cited By ~ 44

Author(s):

Richard A Murphy ◽

Christopher M Rembold

Keyword(s):

Smooth Muscle ◽

Light Chain ◽

Myosin Light Chain ◽

Striated Muscle ◽

Smooth Muscle Contraction ◽

Myosin Light Chain Phosphatase ◽

Shortening Velocity ◽

General Applicability ◽

Cross Bridge ◽

Mechanical Transduction

In contrast to striated muscle, both normalized force and shortening velocities are regulated functions of cross-bridge phosphorylation in smooth muscle. Physiologically this is manifested as relatively fast rates of contraction associated with transiently high levels of cross-bridge phosphorylation. In sustained contractions, Ca2+, cross-bridge phosphorylation, and ATP consumption rates fall, a phenomenon termed "latch". This review focuses on the Hai and Murphy (1988a) model that predicted the highly non-linear dependence of force on phosphorylation and a directly proportional dependence of shortening velocity on phosphorylation. This model hypothesized that (i) cross-bridge phosphorylation was obligatory for cross-bridge attachment, but also that (ii) dephosphorylation of an attached cross-bridge reduced its detachment rate. The resulting variety of cross-bridge cycles as predicted by the model could explain the observed dependencies of force and velocity on cross-bridge phosphorylation. New evidence supports modifications for more general applicability. First, myosin light chain phosphatase activity is regulated. Activation of myosin phosphatase is best demonstrated with inhibitory regulatory mechanisms acting via nitric oxide. The second modification of the model incorporates cooperativity in cross-bridge attachment to predict improved data on the dependence of force on phosphorylation. The molecular basis for cooperativity is unknown, but may involve thin filament proteins absent in striated muscle.Key words: chemo-mechanical transduction, activation-contraction coupling, cross-bridge, myosin light chain kinase, myosin light chain phosphatase, phosphorylation, cooperativity.

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Three-dimensional stochastic model of actin–myosin binding in the sarcomere lattice

The Journal of General Physiology ◽

10.1085/jgp.201611608 ◽

2016 ◽

Vol 148 (6) ◽

pp. 459-488 ◽

Cited By ~ 32

Author(s):

Srboljub M. Mijailovich ◽

Oliver Kayser-Herold ◽

Boban Stojanovic ◽

Djordje Nedic ◽

Thomas C. Irving ◽

...

Keyword(s):

Kinetic Models ◽

Striated Muscle ◽

Three Dimensional ◽

Limited Range ◽

Mass Action ◽

Myosin Filament ◽

Mass Action Kinetic ◽

Cross Bridge ◽

Myosin Binding ◽

Cross Bridges

The effect of molecule tethering in three-dimensional (3-D) space on bimolecular binding kinetics is rarely addressed and only occasionally incorporated into models of cell motility. The simplest system that can quantitatively determine this effect is the 3-D sarcomere lattice of the striated muscle, where tethered myosin in thick filaments can only bind to a relatively small number of available sites on the actin filament, positioned within a limited range of thermal movement of the myosin head. Here we implement spatially explicit actomyosin interactions into the multiscale Monte Carlo platform MUSICO, specifically defining how geometrical constraints on tethered myosins can modulate state transition rates in the actomyosin cycle. The simulations provide the distribution of myosin bound to sites on actin, ensure conservation of the number of interacting myosins and actin monomers, and most importantly, the departure in behavior of tethered myosin molecules from unconstrained myosin interactions with actin. In addition, MUSICO determines the number of cross-bridges in each actomyosin cycle state, the force and number of attached cross-bridges per myosin filament, the range of cross-bridge forces and accounts for energy consumption. At the macroscopic scale, MUSICO simulations show large differences in predicted force-velocity curves and in the response during early force recovery phase after a step change in length comparing to the two simplest mass action kinetic models. The origin of these differences is rooted in the different fluxes of myosin binding and corresponding instantaneous cross-bridge distributions and quantitatively reflects a major flaw of the mathematical description in all mass action kinetic models. Consequently, this new approach shows that accurate recapitulation of experimental data requires significantly different binding rates, number of actomyosin states, and cross-bridge elasticity than typically used in mass action kinetic models to correctly describe the biochemical reactions of tethered molecules and their interaction energetics.

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Multi-scale striated muscle contraction model linking sarcomere length-dependent cross-bridge kinetics to macroscopic deformation

Journal of Computational Science ◽

10.1016/j.jocs.2019.101062 ◽

2020 ◽

Vol 39 ◽

pp. 101062

Author(s):

Boban Stojanovic ◽

Marina Svicevic ◽

Ana Kaplarevic-Malisic ◽

Richard J. Gilbert ◽

Srboljub M. Mijailovich

Keyword(s):

Muscle Contraction ◽

Sarcomere Length ◽

Striated Muscle ◽

Multi Scale ◽

Cross Bridge ◽

Macroscopic Deformation

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Regulation of Contraction in Striated Muscle

Physiological Reviews ◽

10.1152/physrev.2000.80.2.853 ◽

2000 ◽

Vol 80 (2) ◽

pp. 853-924 ◽

Cited By ~ 1129

Author(s):

A. M. Gordon ◽

E. Homsher ◽

M. Regnier

Keyword(s):

Binding Sites ◽

Thin Filament ◽

Striated Muscle ◽

Force Development ◽

Cross Bridge ◽

Hydrolysis Products ◽

Strong Binding ◽

Regulation Of Contraction ◽

Myosin Binding ◽

Cross Bridges

Ca2+ regulation of contraction in vertebrate striated muscle is exerted primarily through effects on the thin filament, which regulate strong cross-bridge binding to actin. Structural and biochemical studies suggest that the position of tropomyosin (Tm) and troponin (Tn) on the thin filament determines the interaction of myosin with the binding sites on actin. These binding sites can be characterized as blocked (unable to bind to cross bridges), closed (able to weakly bind cross bridges), or open (able to bind cross bridges so that they subsequently isomerize to become strongly bound and release ATP hydrolysis products). Flexibility of the Tm may allow variability in actin (A) affinity for myosin along the thin filament other than through a single 7 actin:1 tropomyosin:1 troponin (A7TmTn) regulatory unit. Tm position on the actin filament is regulated by the occupancy of NH-terminal Ca2+binding sites on TnC, conformational changes resulting from Ca2+ binding, and changes in the interactions among Tn, Tm, and actin and as well as by strong S1 binding to actin. Ca2+ binding to TnC enhances TnC-TnI interaction, weakens TnI attachment to its binding sites on 1–2 actins of the regulatory unit, increases Tm movement over the actin surface, and exposes myosin-binding sites on actin previously blocked by Tm. Adjacent Tm are coupled in their overlap regions where Tm movement is also controlled by interactions with TnT. TnT also interacts with TnC-TnI in a Ca2+-dependent manner. All these interactions may vary with the different protein isoforms. The movement of Tm over the actin surface increases the “open” probability of myosin binding sites on actins so that some are in the open configuration available for myosin binding and cross-bridge isomerization to strong binding, force-producing states. In skeletal muscle, strong binding of cycling cross bridges promotes additional Tm movement. This movement effectively stabilizes Tm in the open position and allows cooperative activation of additional actins in that and possibly neighboring A7TmTn regulatory units. The structural and biochemical findings support the physiological observations of steady-state and transient mechanical behavior. Physiological studies suggest the following. 1) Ca2+ binding to Tn/Tm exposes sites on actin to which myosin can bind. 2) Ca2+ regulates the strong binding of M·ADP·Pi to actin, which precedes the production of force (and/or shortening) and release of hydrolysis products. 3) The initial rate of force development depends mostly on the extent of Ca2+ activation of the thin filament and myosin kinetic properties but depends little on the initial force level. 4) A small number of strongly attached cross bridges within an A7TmTn regulatory unit can activate the actins in one unit and perhaps those in neighboring units. This results in additional myosin binding and isomerization to strongly bound states and force production. 5) The rates of the product release steps per se (as indicated by the unloaded shortening velocity) early in shortening are largely independent of the extent of thin filament activation ([Ca2+]) beyond a given baseline level. However, with a greater extent of shortening, the rates depend on the activation level. 6) The cooperativity between neighboring regulatory units contributes to the activation by strong cross bridges of steady-state force but does not affect the rate of force development. 7) Strongly attached, cycling cross bridges can delay relaxation in skeletal muscle in a cooperative manner. 8) Strongly attached and cycling cross bridges can enhance Ca2+ binding to cardiac TnC, but influence skeletal TnC to a lesser extent. 9) Different Tn subunit isoforms can modulate the cross-bridge detachment rate as shown by studies with mutant regulatory proteins in myotubes and in in vitro motility assays. These results and conclusions suggest possible explanations for differences between skeletal and cardiac muscle regulation and delineate the paths future research may take toward a better understanding of striated muscle regulation.

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