scholarly journals Cardiac Thin Filament-Mediated Calcium Sensitization Modulates Cross-Bridge Kinetics

2018 ◽  
Vol 114 (3) ◽  
pp. 315a-316a
Author(s):  
Maicon Landim-Vieira ◽  
David Gonzalez-Martinez ◽  
Jamie R. Johnston ◽  
Weikang Ma ◽  
Olga Antipova ◽  
...  
Keyword(s):  
Thin Filament ◽  
Calcium Sensitization ◽  
Cross Bridge

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 Ca2+ Regulation of Rabbit Skeletal Muscle Thin Filament Sliding: Role of Cross-Bridge Number

2003 ◽  
Vol 85 (3) ◽  
pp. 1775-1786 ◽  
Author(s):  
Bo Liang ◽  
Ying Chen ◽  
Chien-Kao Wang ◽  
Zhaoxiong Luo ◽  
Michael Regnier ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Rabbit Skeletal Muscle ◽  
Cross Bridge ◽  
Muscle Thin Filament ◽  
Bridge Number

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 Three-dimensional image reconstruction of insect flight muscle. I. The rigor myac layer.

1989 ◽  
Vol 109 (3) ◽  
pp. 1085-1102 ◽  
Author(s):  
K A Taylor ◽  
M C Reedy ◽  
L Córdova ◽  
M K Reedy
Keyword(s):  
Thin Filament ◽  
Flight Muscle ◽  
Insect Flight ◽  
Three Dimensional ◽  
Bridge Structure ◽  
Insect Flight Muscle ◽  
Single Filament ◽  
Cross Bridge ◽  
Cross Bridges

We have obtained detailed three-dimensional images of in situ cross-bridge structure in insect flight muscle by electron microscopy of multiple tilt views of single filament layers in ultrathin sections, supplemented with data from thick sections. In this report, we describe the images obtained of the myac layer, a 25-nm longitudinal section containing a single layer of alternating myosin and actin filaments. The reconstruction reveals averaged rigor cross-bridges that clearly separate into two classes constituting lead and rear chevrons within each 38.7-nm axial repeat. These two classes differ in tilt angle, size and shape, density, and slew. This new reconstruction confirms our earlier interpretation of the lead bridge as a two-headed cross-bridge and the rear bridge as a single-headed cross-bridge. The importance of complementing tilt series with additional projections outside the goniometer tilt range is demonstrated by comparison with our earlier myac layer reconstruction. Incorporation of this additional data reveals new details of rigor cross-bridge structure in situ which include clear delineation of (a) a triangular shape for the lead bridge, (b) a smaller size for the rear bridge, and (c) density continuity across the thin filament in the lead bridge. Within actin's regular 38.7-nm helical repeat, local twist variations in the thin filament that correlate with the two cross-bridge classes persist in this new reconstruction. These observations show that in situ rigor cross-bridges are not uniform, and suggest three different myosin head conformations in rigor.

scholarly journals Nebulin increases thin filament stiffness and force per cross-bridge in slow-twitch soleus muscle fibers

2018 ◽  
Vol 150 (11) ◽  
pp. 1510-1522 ◽  
Author(s):  
Masataka Kawai ◽  
Tarek S. Karam ◽  
Justin Kolb ◽  
Li Wang ◽  
Henk L. Granzier
Keyword(s):  
Soleus Muscle ◽  
Thin Filament ◽  
Muscle Fibers ◽  
Force Generation ◽  
Filament Length ◽  
Wild Type ◽  
Sinusoidal Analysis ◽  
Cross Bridge ◽  
Significant Difference ◽  
Slow Twitch

Nebulin (Neb) is associated with the thin filament in skeletal muscle cells, but its functions are not well understood. For this goal, we study skinned slow-twitch soleus muscle fibers from wild-type (Neb+) and conditional Neb knockout (Neb−) mice. We characterize cross-bridge (CB) kinetics and the elementary steps of the CB cycle by sinusoidal analysis during full Ca2+ activation and observe that Neb increases active tension 1.9-fold, active stiffness 2.7-fold, and rigor stiffness 3.0-fold. The ratio of stiffness during activation and rigor states is 62% in Neb+ fibers and 68% in Neb− fibers. These are approximately proportionate to the number of strongly attached CBs during activation. Because the thin filament length is 15% shorter in Neb− fibers than in Neb+ fibers, the increase in force per CB in the presence of Neb is ∼1.5 fold. The equilibrium constant of the CB detachment step (K2), its rate (k2), and the rate of the reverse force generation step (k−4) are larger in Neb+ fibers than in Neb− fibers. The rates of the force generation step (k4) and the reversal detachment step (k−2) change in the opposite direction. These effects can be explained by Le Chatelier’s principle: Increased CB strain promotes less force-generating state(s) and/or detached state(s). Further, when CB distributions among the six states are calculated, there is no significant difference in the number of strongly attached CBs between fibers with and without Neb. These results demonstrate that Neb increases force per CB. We also confirm that force is generated by isomerization of actomyosin (AM) from the AM.ADP.Pi state (ADP, adenosine diphophate; Pi, phosphate) to the AM*ADP.Pi state, where the same force is maintained after Pi release to result in the AM*ADP state. We propose that Neb changes the actin (and myosin) conformation for better ionic and hydrophobic/stereospecific AM interaction, and that the effect of Neb is similar to that of tropomyosin.

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

Regulation of Contraction in Striated Muscle

2000 ◽  
Vol 80 (2) ◽  
pp. 853-924 ◽  
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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