scholarly journals Radial forces within muscle fibers in rigor.

1981 ◽  
Vol 77 (1) ◽  
pp. 49-64 ◽  
Author(s):  
D W Maughan ◽  
R E Godt
Keyword(s):  
Muscle Fibers ◽  
Thick Filament ◽  
Longitudinal Force ◽  
Radial Force ◽  
Bathing Medium ◽  
High Molecular Weight Polymer ◽  
Molecular Weight Polymer ◽  
Cross Bridge ◽  
Radial Forces ◽  
Cross Bridges

Considering the widely accepted cross-bridge model of muscle contraction (Huxley. 1969. Science [Wash. D. C.]. 164:1356-1366), one would expect that attachment of angled cross-bridges would give rise to radial as well as longitudinal forces in the muscle fiber. These forces would tend, in most instances, to draw the myofilaments together and to cause the fiber to decrease in width. Using optical techniques, we have observed significant changes in the width of mechanically skinned frog muscle fibers when the fibers are put into rigor by deleting ATP from the bathing medium. Using a high molecular weight polymer polyvinylpyrrolidone (PVP-40; number average mol. wt. (Mn) = 40,000) in the bathing solution, we were able to estimate the magnitude of the radial forces by shrinking the relaxed fiber to the width observed with rigor induction. With rigor, fiber widths decreased up to approximately 10%, with shrinking being greater at shorter sarcomere spacing and at lower PVP concentrations. At higher PVP concentrations, some fibers actually swelled slightly. Radial pressures seen with rigor in 2 and 4% PVP ranged up to 8.9 x 10(3) N/m2. Upon rigor induction, fibers exerted a longitudinal force of approximately 1 x 10(5) N/m2 that was inhibited by high PVP concentrations (greater than or equal to 13%). In very high PVP concentrations (greater than or equal to 20%), fibers exerted an anomalous force, independent of ATP, which ranged up to 6 x 10(4) N/m2 at 60% PVP. Assuming that all the radial force is the result of cross-bridge attachment, we calculated that rigor cross-bridges exert a radial force of 0.2 x 1.2 x 10(-9) N per thick filament in sarcomeres near rest length. This force is of roughly the same order of magnitude as the longitudinal force per thick filament in rigor contraction or in maximal (calcium-activated) contraction of skinned fibers in ATP-containing solutions. Inasmuch as widths of fibers stretched well beyond overlap of thick and thin filaments decreased with rigor, other radially directed forces may be operating in parallel with cross-bridge forces.

scholarly journals Series-to-parallel transition in the filament lattice of airway smooth muscle

2000 ◽  
Vol 89 (3) ◽  
pp. 869-876 ◽  
Author(s):  
Chun Y. Seow ◽  
Victor R. Pratusevich ◽  
Lincoln E. Ford
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Muscle Length ◽  
Thick Filament ◽  
Cycling Rate ◽  
Cross Bridge ◽  
Parallel Change ◽  
Force Velocity ◽  
Cross Bridges ◽  
Trachealis Muscle

Force-velocity curves measured at different times during tetani of sheep trachealis muscle were analyzed to assess whether velocity slowing could be explained by thick-filament lengthening. Such lengthening increases force by placing more cross bridges in parallel on longer filaments and decreases velocity by reducing the number of filaments spanning muscle length. From 2 s after the onset of stimulation, when force had achieved 42% of it final value, to 28 s, when force had been at its tetanic plateau for ∼15 s, velocity decreases were exactly matched by force increases when force was adjusted for changes in activation, as assessed from the maximum power value in the force-velocity curves. A twofold change in velocity could be quantitatively explained by a series-to-parallel change in the filament lattice without any need to postulate a change in cross-bridge cycling rate.

Effect of Pi on unloaded shortening velocity of slow and fast mammalian muscle fibers

2002 ◽  
Vol 282 (4) ◽  
pp. C647-C653 ◽  
Author(s):  
Jeffrey J. Widrick
Keyword(s):  
Fiber Type ◽  
Muscle Fibers ◽  
Medial Gastrocnemius ◽  
Type I ◽  
Shortening Velocity ◽  
Cross Bridge ◽  
Skinned Muscle ◽  
Specific Effects ◽  
Cross Bridges ◽  
Bridge Models

Chemically skinned muscle fibers, prepared from the rat medial gastrocnemius and soleus, were subjected to four sequential slack tests in Ca2+-activating solutions containing 0, 15, 30, and 0 mM added Pi. Pi (15 and 30 mM) had no effect on the unloaded shortening velocity ( V o) of fibers expressing type IIb myosin heavy chain (MHC). For fibers expressing type I MHC, 15 mM Pi did not alter V o, whereas 30 mM Pireduced V o to 81 ± 1% of the original 0 mM Pi value. This effect was readily reversible when Pi was lowered back to 0 mM. These results are not compatible with current cross-bridge models, developed exclusively from data obtained from fast fibers, in which V o is independent of Pi. The response of the type I fibers at 30 mM Pi is most likely the result of increased internal drag opposing fiber shortening resulting from fiber type-specific effects of Pi on cross bridges, the thin filament, or the rate-limiting step of the cross-bridge cycle.

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.

scholarly journals Bridgelike interconnections between thick filaments in stretched skeletal muscle fibers observed by the freeze-fracture method.

1986 ◽  
Vol 102 (3) ◽  
pp. 1093-1098 ◽  
Author(s):  
S Suzuki ◽  
G H Pollack
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibers ◽  
Freeze Fracture ◽  
Thick Filament ◽  
Rapid Freezing ◽  
Semitendinosus Muscle ◽  
Thin Filaments ◽  
Thick Filaments ◽  
Cross Bridges ◽  
Half Length

The ultrastructure of frog semitendinosus muscle was explored using the freeze-fracture, deep-etch, rotary-shadowing technique. Mechanically skinned fibers were stretched to decrease or eliminate the overlap of thick and thin filaments before rapid freezing with liquid propane. In relaxed, contracting, and rigor fibers, a significant number of bridgelike interconnections, distinct from those observed in the M-region, were observed between adjacent thick filaments in the non-overlap region. Their half-length and diameter corresponded approximately to the known dimensions of the cross-bridge (or myosin S-1). The interconnection may thus be formed by the binding of two apposed cross-bridges projecting from adjacent thick filaments. Fixation with 0.5% glutaraldehyde for 5-10 min before freezing effectively preserved these structures. The results indicate that the interconnections are genuine structures that appear commonly in stretched muscle fibers. They may play a role in stabilizing the thick filament lattice, and possibly in the contractile process.

scholarly journals Decreased thin filament density and length in human atrophic soleus muscle fibers after spaceflight

2000 ◽  
Vol 88 (2) ◽  
pp. 567-572 ◽  
Author(s):  
Danny A. Riley ◽  
James L. W. Bain ◽  
Joyce L. Thompson ◽  
Robert H. Fitts ◽  
Jeffrey J. Widrick ◽  
...  
Keyword(s):  
Soleus Muscle ◽  
Thin Filament ◽  
Sarcomere Length ◽  
Muscle Fibers ◽  
Thick Filament ◽  
Thin Filaments ◽  
Contraction Velocity ◽  
Cross Bridge ◽  
Filament Spacing

Soleus muscle fibers were examined electron microscopically from pre- and postflight biopsies of four astronauts orbited for 17 days during the Life and Microgravity Sciences Spacelab Mission (June 1996). Myofilament density and spacing were normalized to a 2.4-μm sarcomere length. Thick filament density (∼1,062 filaments/μm2) and spacing (∼32.5 nm) were unchanged by spaceflight. Preflight thin filament density (2,976/μm2) decreased significantly ( P < 0.01) to 2,215/μm2 in the overlap A band region as a result of a 17% filament loss and a 9% increase in short filaments. Normal fibers had 13% short thin filaments. The 26% decrease in thin filaments is consistent with preliminary findings of a 14% increase in the myosin-to-actin ratio. Lower thin filament density was calculated to increase thick-to-thin filament spacing in vivo from 17 to 23 nm. Decreased density is postulated to promote earlier cross-bridge detachment and faster contraction velocity. Atrophic fibers may be more susceptible to sarcomere reloading damage, because force per thin filament is estimated to increase by 23%.

scholarly journals Suppression of muscle contraction by vanadate. Mechanical and ligand binding studies on glycerol-extracted rabbit fibers.

1985 ◽  
Vol 86 (3) ◽  
pp. 305-327 ◽  
Author(s):  
J A Dantzig ◽  
Y E Goldman
Keyword(s):  
Muscle Fibers ◽  
Adenosine Diphosphate ◽  
Order Rate Constant ◽  
Rabbit Muscle ◽  
Binding Studies ◽  
Tension Development ◽  
Cross Bridge ◽  
Initial Rise ◽  
Cross Bridges ◽  
Myosin X

The suppression of tension development by orthovanadate (Vi) was studied in mechanical experiments and by measuring the binding of radioactive Vi and nucleotides to glycerol-extracted rabbit muscle fibers. During active contractions, Vi bound to the cross-bridges and suppressed tension with an apparent second-order rate constant of 1.34 X 10(3) M-1s-1. The half-saturation concentration for tension suppression was 94 microM Vi. The incubation of fibers in Vi relaxing or rigor solutions prior to initiation of active contractions had little effect on the initial rise of active tension. The addition of adenosine diphosphate (ADP) and Vi to fibers in rigor did not cause relaxation. Suppression of tension only developed during cross-bridge cycling. After slow relaxation from rigor in 1 mM Vi and low (50 microM) MgATP concentration (0 Ca2+), radioactive Vi and ADP were trapped within the fiber. This finding indicated the formation of a stable myosin X ADP X Vi complex, as has been reported in biochemical experiments with isolated myosin. Vi and ADP trapped within the fibers were released only by subsequent cross-bridge attachment. Vi and ADP were preferentially trapped under conditions of cross-bridge cycling in the presence of ATP rather than in relaxed fibers or in rigor with ADP. These results indicate that in the normal cross-bridge cycle, inorganic phosphate (Pi) is released from actomyosin before ADP. The resulting actomyosin X ADP intermediate can bind Vi and Pi. This intermediate probably supports force. Vi behaves as a close analogue of Pi in muscle fibers, as it does with isolated actomyosin.

Viscoelastic properties of cross bridges in cardiac muscle

1995 ◽  
Vol 268 (3) ◽  
pp. H987-H998
Author(s):  
M. E. De Winkel ◽  
T. Blange ◽  
B. W. Treijtel
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibers ◽  
Ventricular Myocardium ◽  
Partial Recovery ◽  
Cross Bridge ◽  
Skeletal Muscle Fibers ◽  
Freeze Dried ◽  
Length Changes ◽  
Cross Bridges ◽  
Ventricular Trabeculae

Tension responses of rat right ventricular trabeculae to fast length changes are measured with microsecond resolution to obtain information about elastic properties of ventricular myocardium. Responses of these isometrically mounted trabeculae at 22 degrees C to fast length changes completed within 30 microseconds at 22 degrees C to fast length changes completed within 30 microseconds were similar in shape to those of skeletal muscle fibers. Results of quantitative evaluation of responses are interpreted in terms of cross-bridge properties. An upper bound for the elastic range of cross bridges in trabeculae, derived from the maximal developed force during Ca2+ activation and from stiffness in rigor, has been estimated as 8.4 +/- 2.2 nm. Their working stroke, estimated from the tension loss in the rigor state due to a shortening and from tension remaining after (partial) recovery, was 20 +/- 4 nm. The estimated working stroke of cross bridges is about three times larger in trabeculae than in freeze-dried skeletal muscle fibers of the frog at 4 degrees C, which points to important differences between cross-bridge mechanisms of contraction in cardiac and skeletal muscle.

scholarly journals Measuring myosin cross-bridge attachment time in activated muscle fibers using stochastic vs. sinusoidal length perturbation analysis

2011 ◽  
Vol 110 (4) ◽  
pp. 1101-1108 ◽  
Author(s):  
Bertrand C. W. Tanner ◽  
Yuan Wang ◽  
David W. Maughan ◽  
Bradley M. Palmer
Keyword(s):  
White Noise ◽  
Striated Muscle ◽  
Flight Muscle ◽  
Noise Analysis ◽  
Muscle Fibers ◽  
White Noise Analysis ◽  
Sinusoidal Analysis ◽  
Cross Bridge ◽  
Cross Bridges ◽  
Time Required

The average time myosin cross bridges remain bound to actin ( ton) can be measured by sinusoidal length perturbations (sinusoidal analysis) of striated muscle fibers using recently developed analytic methods. This approach allows measurements of ton in preparations possessing a physiologically relevant myofilament lattice. In this study, we developed an approach to measure ton in 5–10% of the time required for sinusoidal analysis by using stochastic length perturbations (white noise analysis). To compare these methods, we measured the influence of MgATP concentration ([MgATP]) on ton in demembranated myocardial strips from mice, sampling muscle behavior from 0.125 to 200 Hz with a 20-s burst of white noise vs. a 300-s series of sinusoids. Both methods detected a similar >300% increase in ton as [MgATP] decreased from 5 to 0.25 mM, differing by only 3–14% at any [MgATP]. Additional experiments with Drosophila indirect flight muscle fibers demonstrated that faster cross-bridge cycling kinetics permit further reducing of the perturbation time required to measure ton. This reduced sampling time allowed strain-dependent measurements of ton in flight muscle fibers by combining 10-s bursts of white noise during periods of linear shortening and lengthening. Analyses revealed longer ton values during shortening and shorter ton values during lengthening. This asymmetry may provide a mechanism that contributes to oscillatory energy transfer between the flight muscles and thoracic cuticle to power flight. This study demonstrates that white noise analysis can detect underlying molecular processes associated with dynamic muscle contraction comparable to sinusoidal analysis, but in a fraction of the time.

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