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  • 1
    Electronic Resource
    Electronic Resource
    Changes in the filament lattice of skeletal muscle fibres induced by changes in osmotic pressure, sarcomere length and the number of crossbridges (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 866-873 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Equatorial small-angle X-ray diffraction patterns offer the possibility of obtaining detailed knowledge about interfilament distance and mass distribution of the myofilament lattice of skeletal muscle. These patterns of skinned frog-muscle fibres have been studied as a function of changes in the incubation solution using the Synchrotron Radiation Source in Daresbury (England). The results of these X-ray diffraction measurements and the results of measurements of the elastic properties of single muscle fibres, with microsecond time resolution, enabled an insight to be gained into the mechanism of muscle contraction. Interfilament distance decreased with increasing osmotic pressure in the absence of free calcium, whereas the mass distribution within the filament lattice did not change. Similar changes in the interfilament distance could be obtained either by decreasing the ionic strength in the absence of free calcium or by increasing the concentration of free calcium of the incubation solution. In both cases, however, mass distribution within the filament lattice also changed, which indicates that under these conditions the number of operating actomyosin complexes in the muscle fibre (crossbridges) tends to increase. The changes in interfilament distance and mass distribution that occur which depend on the free calcium concentration can be explained by a changed number of force-generating crossbridges. In the case of changes induced by ionic strength two effects interfere. Only part of the change in lattice spacing can be explained by an increased number of weakly attached crossbridges; the remaining part is caused by a process similar to that in the case of osmotic pressure. The effect of weakly attached crossbridges in the absence of free calcium under normal ionic strength conditions is small. Therefore, the large decrement in interfilament distance due to an increased sarcomere length, in the absence of free calcium, is not caused by weakly attached crossbridges. Changes in sacromere length, in the presence of free calcium, resulted in changes in the number of force-generating crossbridges. However, the observed effect on interfilament distance cannot be explained solely by the variation of the number of force-generating crossbridges. The results of X-ray diffraction patterns and stiffness measurements of fibres in rigor solutions [absence of ATP (adenosine triphosphate) and calcium] and fibres in calcium solutions indicated that the (force-generating) crossbridges in the latter differ from crossbridges in rigor fibres.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891004740
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  • 2
    Electronic Resource
    Electronic Resource
    The insulin-like effects of a glucose metabolite (bis-PEP) from muscle and erythrocytes
    Amsterdam : Elsevier
    FEBS Letters 72 (1976), S. 58-62 
    Details
    ISSN: 0014-5793
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0014-5793(76)80812-5
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  • 3
    Electronic Resource
    Electronic Resource
    Cross-bridge stiffness in Ca2+-activated skinned single muscle fibres (1992)
    Springer
    Pflügers Archiv 420 (1992), S. 434-445 
    Details
    ISSN: 1432-2013
    Keywords: Skeletal muscle ; X-ray ; Tension transients ; Skinned fibres ; Stiffness ; Elastic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Tension transients, in response to small and rapid length changes (completed within 40 μs), 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 (d 10)of Ca2+-activated single frog muscle fibres decreased with increasing isometric force, whereas the intensity ratio (I 11/I10)increased linearly with increasing isometric force. From experiments in which dextran (MW 200000 Da) was added, it followed that such a change in filament spacing would modify passive stiffness. The d 10value of relaxed fibres decreased and stiffness increased with increasing concentrations of the polymer dextran, whereas I 11/I10remained 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 C 1, 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 complicance of activated fibres is located in the crossbridges.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374617
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  • 4
    Electronic Resource
    Electronic Resource
    Tension development and calcium sensitivity in skinned muscle fibres of the frog (1985)
    Springer
    Pflügers Archiv 405 (1985), S. 19-23 
    Details
    ISSN: 1432-2013
    Keywords: Muscle ; Muscle contraction ; Calcium sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Calcium activated isometric tension development was measured in single skinned muscle fibres of the ileofibularis muscle of the frog. The experiments were carried out at 5°C, pH=6.9, 1 mM free Mg2+ and an ionic strength of 160 mM. A Hill curve was fitted to the isometrically developed tension at different Ca2+ concentrations by means of a non-linear least mean square approximation. At a sarcomere length of 2.15 μm, the Ca2+ concentration for half maximum tension (K) was 1.6 μM. This Ca2+ concentration decreased with increasing sarcomere length; at 2.7 μm, K was 1.1 μM and at 3.1 μm, K was 0.9 μM. Therefore, Ca sensitivity is increased at larger sarcomere lengths. Consequently, the optimal sarcomere length for tension development shifted to larger values when the Ca2+ concentration was lowered. Osmotic compression of the fibre at 2.15 μm by means of 5% Dextran also caused an increase in Ca sensitivity (K was 1.0 μM). At 2.7 μm, addition of 5% Dextran hardly affected the Ca sensitivity. The possible role of the interfilament spacing in the explanation of these results discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00591092
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  • 5
    Electronic Resource
    Electronic Resource
    High frequency characteristics of elasticity of skeletal muscle fibres kept in relaxed and rigor state (1994)
    Springer
    Journal of muscle research and cell motility 15 (1994), S. 130-144 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The viscoelastic properties of crossbridges in rigor state are studied by means of application of small length changes, completed within 30 μs, 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 3.12×107 N m-2 at 40 kHz to 1.61×107 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. Similarity of Young's modulus of fibre segments in the activated state and in rigor in the frequency range above 5 kHz strongly suggests that the same state transitions occur in force generating crossbridges in the activated fibre.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00130424
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of actin filament compliance on the interpretation of the elastic properties of skeletal muscle fibres (1997)
    Springer
    Journal of muscle research and cell motility 18 (1997), S. 125-131 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Recently, 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−2. This corresponds to a compliance of 23 pm μm−1 per kN m−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−2 at frequencies below 500 Hz to 55 MN m−2 above 40 kHz
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018649420778
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  • 7
    Electronic Resource
    Electronic Resource
    The complex Young's modulus of skeletal muscle fibre segments in the high frequency range determined from tension transients (1993)
    Springer
    Journal of muscle research and cell motility 14 (1993), S. 302-310 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Stiffness measurements of muscle fibres are often based on application of a length change at one end of the muscle fibre and recording of the following tension change at the other end. In this study a method is developed to determine in the high frequency range (up to 40 kHz) the complex Young's modulus of skeletal muscle fibre as a function of frequency from the tension transient, following a rapid stepwise length change completed within 40 μs. For this purpose both a new mechanical moving part of the displacement generating system and a force transducer with a high natural frequency (70 kHz) had to be developed. In addition to stiffness measurements of a silk fibre to test the displacement generating system and the method of analysis, stiffness of skeletal muscle fibres in relaxed and rigor state have been measured. The complex Young's moduli of relaxed muscle fibres as well as muscle fibres in rigor state are frequency dependent. In both cases the complex Young's modulus increases smoothly with increasing frequency over a range of 250 Hz up to 40 kHz. The phase angles of the responses remained almost constant at a value of 0.3 radians for a fibre in rigor and 0.6 radians for a relaxed fibre. This leads to the conclusion that for muscle fibres in rigor state the recovery in the tension response to a step length change shows a continuous distribution of relaxation times rather than a few discrete ones. Results of our stiffness measurements are compared with results obtained from current viscoelastic models used to describe stiffness of muscle fibre in this frequency range. The frequency dependence of stiffness of muscle fibres in rigor state suggests that the frequency used has to be taken into account while determining the elastic range of a crossbridge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00123095
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