Untitled

Abstract

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.

Viscoelasticity-based MR elastography of skeletal muscle

“…We can therefore speculate about the superposition of changes in both geometry and hierarchy that takes place while the muscle is activated. Attempting to address the complex interplay between macro-and micro-mechanical constituents in muscle by scaling, one may regard cross-bridges between myosin and actin filaments as additional spring elements that are established by activation (Blange et al 1997) and thus change the degree of freedom in the mechanical network of muscle. It was therefore stimulating to observe, in analogy to this microscopic picture, an increasing slope α in our macroscopic G * values upon contraction.…”

Fibrin gels and their clinical and bioengineering applications

“…The softness of the fibrin strand (1.5 to 10 MPa) is evident by comparison of its Young's modulus with that of actin filaments (44 MPa; Blange et al 1997) and microtubules (100-1000 MPa; Mizushima-Sugano et al 1983;Gittes et al 1993). In terms of persistence length, fibrin protofibrils are similar to intermediate filaments (l p Z0.2-1 mm) but much more flexible than either F-actin (l p Z17 mm) or microtubules (l p ZO1 mM) (Wagner et al 2007).…”

Effects of shortening velocity on the stiffness to force ratio during isometric force redevelopment suggest mechanisms of residual force depression

“…While many structures contribute to muscle stiffness in addition to cross bridges 37 , including thick 35 and thin filaments 36 , only cross bridges and titin 21 appear to exhibit activation-dependent stiffness. The stiffness of thick 35 and thin filaments 38 is independent of muscle activation, making any contribution to residual force depression unlikely.…”