Weakly attached cross-bridges in relaxed frog muscle fibers

Jung, D. W. G.; Blangé, T.; Graaf, H. de; Treijtel, B. W.

doi:10.1016/s0006-3495(89)82858-9

Cited by 12 publications

(9 citation statements)

References 21 publications

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“…For rabbit psoas muscle fibres in relaxed state 80% of stiffness has been attributed to weakly attached crosdbridges (Chalovich et al, 1991). Based on extrapolation of stiffness measurements at low ionic strength a value of less than 5% of the number of crossbridges in rigor is reported for frog muscle (Jung et al, 1989) at the ionic strength used in this study, but it is not clear if crossbridges at low ionic strength are comparable to weakly bound crossbridges under more physiological conditions (Huxley & Kress, 1985). The result that change of viscosity of the incubation fluid had no effect on Young's modulus in the relaxed state points, even stronger than in the case of rigor, to another mechanism than just elastic structures in combination with fluid friction.…”

Section: Discussionmentioning

confidence: 71%

“…To be able to compare the values of the model parameters obtained from fibres in relaxed and rigor state the interfilament spacing needed adjustment. Rigor filament spacing can be obtained in a relaxed musde fibre by addition of 3% (w/v) Dextran-500 to the relaxation solution (Jung et al, 1989). For a muscle fibre in relaxed state this basically resulted in a scaling towards higher Young's modulus (17% increase in elastic constant).…”

Section: Discussionmentioning

confidence: 99%

“…The difference in interfilament distance of muscle fibres in relaxed and rigor state, as demonstrated by X-ray measurements (Jung et al, 1989), could affect the difference in amplitude of the Young's mod& as a function of frequency. To investigate the effect of interfilament distance, measurements were performed on muscle fibres incubated in a relaxing solution with 3% (w/v) Dextran added.…”

Section: Interfilament Distancementioning

confidence: 99%

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High frequency characteristics of elasticity of skeletal muscle fibres kept in relaxed and rigor state

Winkel

Blangé

Treijtel

1994

J Muscle Res Cell Motil

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The viscoelastic properties of crossbridges in rigor state are studied by means of application of small length changes, completed within 30 microseconds, to isometric skinned fibre segments of the iliofibularis muscle of the frog in relaxed and rigor state and measurement of the tension response. Results are expressed as a complex Young's modulus, the real part of which denotes normalized stiffness, while the imaginary part denotes normalized viscous mechanical impedance. Young's modulus was examined over a wide frequency range varying from 5 Hz up to 50 kHz. Young's modulus can be interpreted in terms of stiffness and viscous friction of the half-sarcomere or in terms of elastic changes in tension and recovery upon a step length change. The viscoelastic properties of half-sarcomeres of muscle fibre segments in rigor state showed strong resemblance to those of activated fibres in that shortening a muscle fibre in rigor state resulted in an immediate drop in tension, after which half of the drop in tension was recovered. The following slower phases of tension recovery--a subsequent drop in tension and slow completion of tension recovery--as seen in the activated state, do not occur in rigor state. The magnitude of Young's moduli of fibres in rigor state generally decreased from a value of 3.12 x 10(7) N m-2 at 40 kHz to 1.61 x 10(7) N m-2 at about 100 Hz. Effects of increased viscosity of the incubation medium, decreased interfilament distance in the relaxed state and variation of rigor tension upon frequency dependence of complex Young's modulus have been investigated. Variation of tension of crossbridges in rigor state influenced to some extent the frequency dependence of the Young's modulus. Recovery in relaxed state is not dependent on the viscosity of the medium. Recovery in rigor is slowed down at raised viscosity of the incubation medium, but less than half the amount expected if viscosity of the medium would be the cause of internal friction of the half-sarcomere. Internal friction of the half-sarcomere in the relaxed fibre at the same interfilament distance as in rigor is different from internal friction in rigor. It will be concluded that time necessary for recovery in rigor cannot be explained by friction due to the incubation medium. Instead, recovery in rigor expressed by the frequency dependence of the Young's modulus has to be due to intrinsic properties of crossbridges. These intrinsic properties can be explained by the occurrence of state transitions of crossbridges in rigor.(ABSTRACT TRUNCATED AT 400 WORDS)

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Section: Discussionmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 99%

Section: Interfilament Distancementioning

confidence: 99%

See 1 more Smart Citation

High frequency characteristics of elasticity of skeletal muscle fibres kept in relaxed and rigor state

Winkel

Blangé

Treijtel

1994

J Muscle Res Cell Motil

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“…However, a closer inspection of the relaxed state shows that the apparent elastic constants for relaxed muscle fibres increase substantially when the ionic strength is decreased (Jung et al, 1989). This is commonly associated with an increase in the number of weakly bound cross-bridges.…”

Section: Discussionmentioning

confidence: 99%

“…As the number of weakly bound crossbridges is very small (Jung et al, 1989), we ignore a possible reduction of weakly bound bridges upon activation. Based on the elastic constant Z 4 , corresponding to the Young's modulus around 100 Hz, we find that the filament Young's modulus must be larger than 33 MN m ÿ 2 .…”

Section: Partially Activated Muscle Fibresmentioning

confidence: 99%

Untitled

Blangé

Heide

Treijtel

et al. 1997

Journal of Muscle Research and Cell Motility

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The effect of actin filament compliance on the interpretation of the elastic properties of skeletal muscle fibres Blange, T.; van der Heide, U.A.; Treijtel, B.W.; de Beer, E.L. Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. SummaryRecently, X-ray diffraction studies provided direct evidence for an appreciable length change in the actin filament upon activation. This finding has profound implications on the interpretation of the elastic properties of skeletal muscle fibre.In this study we determined the compliance of the actin filament during activation, using the data obtained previously from quick stretch and release experiments on skeletal muscle fibres of the frog. The effects of filament compliance are demonstrated clearly in the elastic properties of partially activated fibres. The low-frequency elasticity increases linearly with tension, reflecting an increase in the number of force-producing cross-bridges. At higher frequencies, this linearity is lost. In this study we describe the data consistently in terms of a cross-bridge stiffness increasing linearly with tension and a constant Young's modulus for the actin filament of 44 MN m per kN m ÿ 2 tension developed. Using this value for the actin filament Young's modulus, its contribution to the elastic properties of skeletal muscle fibre of the frog is considered in rigor and relaxation. The filament compliance hardly affects the overall elasticity of the musle fibre in relaxation. In contrast, it contributes to a large extent to the overall elasticity in rigor. Taking account of the filament compliance, we find that the Young's modulus in rigor exhibits an increase from 14 MN m ÿ 2 at frequencies below 500 Hz to 55 MN m ÿ 2 above 40 kHz.

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Cross-bridge stiffness in Ca2+-activated skinned single muscle fibres

et al. 1992

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Tension transients, in response to small and rapid length changes (completed within 40 microseconds), were obtained from skinned single frog muscle fibres incubated in activating solutions with varying concentrations of Ca2+. The first 2 ms of these transients were described by a linear model in which the fibre is regarded as a rod composed of infinitesimally small, identical segments containing a mass, one undamped elastic element and in the case of relaxed fibres two damped elastic elements in series, or in the case of activated fibres three such elastic elements in series. The stiffness of activated fibres, expressed in elastic constants or apparent elastic constants, increased with increasing concentrations of Ca2+. All the damped elastic constants that were necessary to describe the tension responses of activated fibres were proportional to isometric tension. However, the undamped elastic constant did not increase linearly with increasing isometric tension. Equatorial X-ray diffraction patterns were obtained from single frog muscle fibres under similar conditions as under which the tension transients were obtained. The filament spacing (d10) of Ca(2+)-activated single frog muscle fibres decreased with increasing isometric force, whereas the intensity ratio (I11/I10) increased linearly with increasing isometric force. From experiments in which dextran (MW 200,000 Da) was added, it followed that such a change in filament spacing would modify passive stiffness. The d10 value of relaxed fibres decreased and stiffness increased with increasing concentrations of the polymer dextran, whereas I11/I10 remained constant. The relation of stiffness and filament spacing with concentration of dextran was used to eliminate the effect of decreased filament spacing on stiffness of activated fibres. After correction for changes in filament spacing the undamped complicance C1, normalized to tension, was not constant, but increased with increasing isometric tension. If we assume that isometric tension is proportional to the number of force generating cross-bridges, this means that only part of the undamped compliance of activated fibres is located in the cross-bridges.

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Weakly attached cross-bridges in relaxed frog muscle fibers

Cited by 12 publications

References 21 publications

High frequency characteristics of elasticity of skeletal muscle fibres kept in relaxed and rigor state

High frequency characteristics of elasticity of skeletal muscle fibres kept in relaxed and rigor state

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Cross-bridge stiffness in Ca2+-activated skinned single muscle fibres

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