scholarly journals Sarcomere mechanics in striated muscles: from molecules to sarcomeres to cells

2017 ◽  
Vol 313 (2) ◽  
pp. C134-C145 ◽  
Author(s):  
Dilson E. Rassier
Keyword(s):  
Muscle Contraction ◽  
Sarcomere Length ◽  
Muscle Fibers ◽  
Strong Support ◽  
Common Mechanism ◽  
Striated Muscles ◽  
Cross Bridge ◽  
The Cross ◽  
Sliding Filament Theory ◽  
Permeabilized Fibers

Muscle contraction is commonly associated with the cross-bridge and sliding filament theories, which have received strong support from experiments conducted over the years in different laboratories. However, there are studies that cannot be readily explained by the theories, showing 1) a plateau of the force-length relation extended beyond optimal filament overlap, and forces produced at long sarcomere lengths that are higher than those predicted by the sliding filament theory; 2) passive forces at long sarcomere lengths that can be modulated by activation and Ca2+, which changes the force-length relation; and 3) an unexplained high force produced during and after stretch of activated muscle fibers. Some of these studies even propose “new theories of contraction.” While some of these observations deserve evaluation, many of these studies present data that lack a rigorous control and experiments that cannot be repeated in other laboratories. This article reviews these issues, looking into studies that have used intact and permeabilized fibers, myofibrils, isolated sarcomeres, and half-sarcomeres. A common mechanism associated with sarcomere and half-sarcomere length nonuniformities and a Ca2+-induced increase in the stiffness of titin is proposed to explain observations that derive from these studies.

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.

Effects of blebbistatin and Ca2+ concentration on force produced during stretch of skeletal muscle fibers

2010 ◽  
Vol 299 (5) ◽  
pp. C1127-C1135 ◽  
Author(s):  
Fabio C. Minozzo ◽  
Dilson E. Rassier
Keyword(s):  
Skeletal Muscle ◽  
Sarcomere Length ◽  
Muscle Fibers ◽  
Critical Force ◽  
Power Stroke ◽  
Optimal Length ◽  
Maximal Force ◽  
The Cross ◽  
Cross Bridges ◽  
Two Phases

When activated muscle fibers are stretched at low speeds [≤2 optimal length ( Lo)/s], force increases in two phases, marked by a change in slope [critical force (Pc)] that happens at a critical sarcomere length extension ( Lc). Some studies attribute Pc to the number of attached cross bridges before stretch, while others attribute it to cross bridges in a pre-power-stroke state. In this study, we reinvestigated the mechanisms of forces produced during stretch by altering either the number of cross bridges attached to actin or the cross-bridge state before stretch. Two sets of experiments were performed: 1) activated fibers were stretched by 3% Lo at speeds of 1.0, 2.0, and 3.0 Lo/s in different pCa2+ (4.5, 5.0, 5.5, 6.0), or 2) activated fibers were stretched by 3% Lo at 2 Lo/s in pCa2+ 4.5 containing either 5 μM blebbistatin(+/−) or its inactive isomer (+/+). All stretches started at a sarcomere length (SL) of 2.5 μm. When fibers were activated at a pCa2+ of 4.5, Pc was 2.47 ± 0.11 maximal force developed before stretch (Po) and decreased with lower concentrations of Ca2+. Lc was not Ca2+ dependent; the pooled experiments provided a Lc of 14.34 ± 0.34 nm/half-sarcomere (HS). Pc and Lc did not change with velocities of stretch. Fibers activated in blebbistatin(+/−) showed a higher Pc (2.94 ± 0.17 Po) and Lc (16.30 ± 0.38 nm/HS) than control fibers (Pc 2.31 ± 0.08 Po; Lc 14.05 ± 0.63 nm/HS). The results suggest that forces produced during stretch are caused by both the number of cross bridges attached to actin and the cross bridges in a pre-power-stroke state. Such cross bridges are stretched by large amplitudes before detaching from actin and contribute significantly to the force developed during stretch.

Mathematical aspects of the cross-bridge mechanism in muscle contraction

1983 ◽  
Vol 7 (6) ◽  
pp. 661-683 ◽  
Author(s):  
Valeriano Comincioli ◽  
Alessandro Torelli
Keyword(s):  
Muscle Contraction ◽  
Cross Bridge ◽  
The Cross ◽  
Cross Bridge Mechanism

BDM affects nucleotide binding and force generation steps of the cross-bridge cycle in rabbit psoas muscle fibers

1994 ◽  
Vol 266 (2) ◽  
pp. C437-C447 ◽  
Author(s):  
Y. Zhao ◽  
M. Kawai
Keyword(s):  
Equilibrium Constants ◽  
Muscle Fibers ◽  
Psoas Muscle ◽  
Isometric Tension ◽  
Activation Mechanism ◽  
Phosphate Binding ◽  
Rabbit Psoas ◽  
Cross Bridge ◽  
The Cross ◽  
Cross Bridges

The effect of 2,3-butanedione monoxime (BDM) on elementary steps of the cross-bridge cycle was studied with the sinusoidal analysis technique in skinned rabbit psoas muscle fibers. Our results showed that isometric tension and stiffness decreased progressively with an increase in the BDM concentration. The MgATP and MgADP binding constants increased 27 and 6 times, respectively, when BDM was increased from 0 to 18 mM, whereas the phosphate binding constant did not change significantly. The equilibrium constants of the ATP isomerization and detachment step were not sensitive to BDM, whereas the equilibrium constant of the attachment (power stroke) step decreased with BDM. Thus, in the presence of BDM, the number of attached cross bridges decreases; more cross bridges accumulate in the detached state, causing isometric tension and stiffness to decline. However, our detailed analysis shows that the decrease in the number of attached cross bridges is approximately 40%, which is not adequate to account for the 84% decrease in the isometric tension when 18 mM BDM was present. Therefore we suggest that a thin-filament activation mechanism is also affected by BDM.

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

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

Length dependence of active force production in skeletal muscle

1999 ◽  
Vol 86 (5) ◽  
pp. 1445-1457 ◽  
Author(s):  
D. E. Rassier ◽  
B. R. MacIntosh ◽  
W. Herzog
Keyword(s):  
Skeletal Muscle ◽  
Muscle Contraction ◽  
Sarcomere Length ◽  
Length Change ◽  
In Vivo Studies ◽  
Active Force ◽  
Moment Arm ◽  
Cross Bridge ◽  
Length Relationship

The sliding filament and cross-bridge theories of muscle contraction provide discrete predictions of the tetanic force-length relationship of skeletal muscle that have been tested experimentally. The active force generated by a maximally activated single fiber (with sarcomere length control) is maximal when the filament overlap is optimized and is proportionally decreased when overlap is diminished. The force-length relationship is a static property of skeletal muscle and, therefore, it does not predict the consequences of dynamic contractions. Changes in sarcomere length during muscle contraction result in modulation of the active force that is not necessarily predicted by the cross-bridge theory. The results of in vivo studies of the force-length relationship suggest that muscles that operate on the ascending limb of the force-length relationship typically function in stretch-shortening cycle contractions, and muscles that operate on the descending limb typically function in shorten-stretch cycle contractions. The joint moments produced by a muscle depend on the moment arm and the sarcomere length of the muscle. Moment arm magnitude also affects the excursion (length change) of a muscle for a given change in joint angle, and the number of sarcomeres arranged in series within a muscle fiber determines the sarcomere length change associated with a given excursion.

scholarly journals Contraction transients of skinned muscle fibers: effects of calcium and ionic strength.

1978 ◽  
Vol 72 (5) ◽  
pp. 701-715 ◽  
Author(s):  
J Gulati ◽  
R J Podolsky
Keyword(s):  
Ionic Strength ◽  
Muscle Fibers ◽  
Kinetic Properties ◽  
Cross Bridge ◽  
Skinned Muscle ◽  
The Cross ◽  
Cross Bridge Mechanism ◽  
Low Ionic Strength ◽  
Bridge Number ◽  
Steady Force

Calcium and ionic strength are both known to modify the force developed by skinned frog muscle fibers. To determine how these parameters affect the cross-bridge contraction mechanism, the isotonic velocity transients following step changes in load were studied in solutions in which calcium concentration and ionic strength were varied. Analysis of the motion showed that calcium has no effect on either the null time or the amplitude of the transients. In contrast, the transient amplitude was increased in high ionic strength and was suppressed in low ionic strength. These results are consistent with the idea that calcium affects force in skeletal muscle by modulating the number of force generators in a simple switchlike "on-off" manner and that the steady force at a given calcium level is proportional to cross-bridge number. On the other hand, the effect of ionic strength on force is associated with changes in the kinetic properties of the cross-bridge mechanism.

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