Biological Sciences
Sliding Filament Theory
The Sliding Filament Theory explains how muscles contract at a molecular level. It proposes that during muscle contraction, the thin actin filaments slide past the thick myosin filaments, causing the sarcomere unit to shorten. This process is driven by the interaction of myosin heads with actin filaments, powered by ATP hydrolysis.
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11 Key excerpts on "Sliding Filament Theory"
eBook - PDF- Thomas A. McMahon(Author)
- 2020(Publication Date)
- Princeton University Press(Publisher)
Electrostatic Theories A natural suggestion for the cause of the sliding movement might be that the two filaments carry electric charges of opposite sign, which attract each other and therefore tend to increase the zone of overlap. This mechanism has, in fact, been suggested in various forms (Yu et al., 1970; Nobel and Pollack, 1977). A. F. Huxley (1974, 1979) points out the inability of such models to shorten further than the length where overlap between the actin and myosin filaments The Sliding Movement 87 is complete, or to explain the decreased rate of energy liberation per unit change of length as shortening speed increases. There is also the difficulty of the high potassium ion concentration within the fiber, which would act to screen the charges on the negatively charged filament. Folding Thin Filaments Podolsky (1959) has suggested that the ends of thin filaments first attach to adjacent thick filaments and then the thin filaments shorten by folding in the overlap zone. But electron microscopy subsequently showed that the ends of the thin filaments slide inwards during contraction, even to the point of overlapping each other in the center of the ,4-band (H. E. Huxley, 1964). This is strong evidence against the idea that contraction occurs because the filaments themselves shorten. Evidence for Independent Force Generators Operating Cyclically There are two particularly important pieces of evidence for supposing that the crossbridges are discrete force generators acting independently. (1) Isometric tetanic tension is proportional to the extent of actin-myosin overlap. The experiments by Gordon, A. F. Huxley, and Julian (1966b) using the servo-controlled spot follower device to maintain a set length in a limited portion of a single-fiber preparation were summarized in fig.
eBook - ePubUnderstanding Mammalian Locomotion
Concepts and Applications
- John E. A. Bertram(Author)
- 2016(Publication Date)
- Wiley-Blackwell(Publisher)
E. Huxley, working with R. Niedergerke, and A. F. Huxley, working with J. Hanson – independently reached the conclusion that change in muscle length was caused by two sets of inter-digitating protein filaments, actin and myosin, sliding past one another within the sarcomere. This sliding interaction defined the contractile unit of muscle. Prior to this proposal, the prevailing theory was that protein folding caused changes in muscle length. Sliding Filament Theory was based primarily on the observation that the A-bands of striated muscle do not change length during passive shortening or lengthening of muscle. A-bands are structurally anisotropic regions (“A” for anisotropic) that contain myosin (Figure 3.1) and are characterized by high birefringence. Birefringence, or “double refraction”, is the decomposition of a single ray of light into two rays. Materials with high birefringence produce a large angle between the two rays while materials with low birefringence produce a small angle between the two rays. Differences in birefringence translate into differences in brightness under a polarized light microscope. The observation that the A-bands remain at constant length while the sarcomere lengthens suggested that the actin filaments slide relative to the myosin filaments in the A-bands. Huxley and Hanson (1954) also showed that the actin filaments do not change length by measuring actin filament lengths after the myosin had been removed from muscle at various muscle lengths. FIGURE 3.1 The organization of the sarcomere, the fundamental contractile unit of muscle. Conglomerates of myosin molecule “tails” form the backbones of the myosin filaments. The “heads” of the myosin molecules project from the backbones forming the cross-bridges. During active concentric contraction, the cross-bridges attach to the surrounding actin filaments and undergo a conformational change that pulls the actin and myosin filaments past one another
eBook - PDFMathematical Mechanics: From Particle To Muscle
From Particle to Muscle
- Ellis D Cooper(Author)
- 2011(Publication Date)
- World Scientific(Publisher)
Third, the atomic structures arising from the crys-tallization of actin and myosin now allow one to search for the changes in molecular structure that account for force production [Szent-Gy¨orgyi (2004)]. Gerald H. Pollack, Felix A. Blyakhman, Xiumei Liu, and Ekatarina Nagornyak 2004 Fifty years have passed since the monumental discovery that muscle contraction results from relative sliding between the thick filaments, consisting mainly of myosin , and the thin filaments, consisting mainly of actin [Huxley and Niedergerke (1954)][Hux-ley and Hanson (1954)]. Until the early 1970’s, considerable progress have been achieved in the research field of muscle con-traction. For example, A. F. Huxley and his coworkers put for-ward a contraction model, in which the myofilament sliding is caused by alternate formation and breaking of cross-links between the cross-bridges on the thick filament and the sites on the thin filament, while biochemical studies on acto myosin AT P ase re-actions indicated that, in solution, actin and myosin also repeat attachment-detachment cycles. Thus, when a Cold Spring Har-bor Symposium on the Mechanism of Muscle Contraction was held in 1972, most participants felt that the molecular mecha-nism of muscle contraction would soon be clarified, at least in principle. Contrary to the above “optimistic” expectation, however, we cannot yet give a clear answer to the question, “what makes the filaments slide?” This paper has a dual goal. First it outlines the methods that have evolved to track the time course of sarcomere length with increasingly high precision. Serious attempts at this began roughly at the time the Sliding Filament Theory was introduced in 316 Mathematical Mechanics: From Particle to Muscle the mid-1950s, and have progressed to the point where resolution has reached the nanometer level. Second, and within the context of these developments, it considers one of the more controversial aspects of these developments: stepwise shortening.
eBook - PDF- Edward Bittar(Author)
- 1996(Publication Date)
- Elsevier Science(Publisher)
Chapter 7 The Cellular and Molecular Basis of Skeletal and Cardiac Muscle Contraction MICHELLE PECKHAM Introduction Basic Properties of Muscle Development Contractile Properties Muscle Proteins and Sarcomere Structure Development of the Sliding Filament Theory of Muscle Contraction A.F. Huxley's 1957 Theory Further Structural Approaches Hugh Huxley's 1969 Theory Transient Mechanical Properties Velocity Transients Tension Transients A.F. Huxley and Simmons's 1971 Theory Muscle Stiffness Approaches to Investigate the Energy Source of Muscle Contraction Myosin as an A TPase Activation of Myosin ATPase by Actin Lymn and Taylor Model 1971 Eisenberg and Hill Model 1985 How do the Predicted Free Energy Changes Fit With the Revised Model? Biochemical Experiments with Fibers Caged-ATP Effect of Phosphate on Force Generation 202 202 202 203 206 209 210 213 215 217 217 218 220 220 221 221 222 224 225 225 226 226 227 Principles of Medical Biology, Volume 4 Cell Chemistry and Physiology: Part IV, pages 201-237. Copyright 9 1996 by JAI Press Inc. All rights of reproduction in any form reserved. ISBN: 1-55938-808-0 201 202 MICHELLE PECKHAM Weak and Strong Crossbridges Motility Assays Crystal Structures of Actin and Myosin Subfragment-l Rayment's 1993 Model Summary 229 230 231 233 234 INTRODUCTION Muscle contraction has been studied since the early 1800s (see review by A.F. Huxley, 1980). We now know that actin and myosin are the two proteins essential for force production in skeletal muscle. Each of these proteins is organized into a separate filament, myosin (molecular weight about 500,000) in the thick filaments and actin (molecular weight about 42,000) in the thin filaments. Each thick filament (1.6 lum long) contains about 300 myosin molecules and each thin filament (1.0 ~tm long) about 380 actin molecules. These filaments are organized into a repeating structure called the muscle sarcomere that is 2.2 ~tm long in frog muscle.
eBook - PDF- Hans Neurath(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
The invariance of the axial X-ray reflections in passively stretched muscle was one of the first indications that muscle contraction might involve a process in which the two sets of filaments remain constant in length but simply slide past each other as the sarcomere shortens. The plausibility of this idea was quickly demonstrated by light microscopy studies of muscle which revealed that the A-band and I-filament lengths did in-deed remain constant under a variety of experimental conditions, thus leading two groups (H. E. Huxley and Hanson, 1954; A. F. Huxley and Niedergerke, 1954) to propose simultaneously and independently the Sliding Filament Theory of contraction: When the muscle changes its length, either actively or passively, the arrays of filaments slide past each other at almost constant length; the force for contrac-tion is generated by some process which actively translates one type of fila-ment past the neighboring filaments of the other type. (Huxley, 1970.) It was recognized quite early from selective extraction experiments that the ordered thick filaments of striated muscle are aggregates of several hundred myosin molecules, while the thin filaments are as-semblies of large numbers of the globular protein G-actin (Hanson and Huxley, 1953, 1957). As we now know, both structures contain addi-tional protein components. Starr and Offer (1971) have recently dem-onstrated the presence of a protein having a molecular weight of 140,-000, the C-protein, which is associated with the backbone of the thick filament and which can be visualized in high magnification electron micrographs in the A-bands of longitudinally sectioned muscle as a se-ries of 7-9 transverse stripes flanking the M-line at approximately 440-Â intervals (Huxley, 1966, 1967). Moreover, the regulatory pro-teins, tropomyosin and troponin, have been shown to be associated with the thin filament arrays (Ebashi and Endo, 1968; Weber and Murray, 1973).
eBook - PDFSkeletal Muscle
From Myogenesis to Clinical Relations
- Julianna Cseri(Author)
- 2012(Publication Date)
- IntechOpen(Publisher)
2. Theories of myofilament sliding producing muscle contraction Since the lengths of the thick and thin filament remain unchanged before,during and after the myofilament sliding, i.e. muscle contraction, it seems natural to consider that the myofilament sliding is caused by cyclic formation and breaking of linkages between the S-1 heads on the thick filaments and the corresponding sites on the thin filaments. The cyclic interaction between the S-1 head and the thin filament is obviously coupled with ATP hydrolysis. Most theories about mechanism of muscle contraction have been based on this idea. 2.1. Attachment-detachment cycle between the S-1 head on the thick filament and the sites on the thin filaments Fig. 2 shows diagrams illustrating hypothetical attachment-detachment cycle between the myosin S-1 head and the corresponding site on the thin filaments, put forward by H.E.Huxley [6]. In each diagram, three rectangular-shaped S-1 heads extend from the thick filament upwards to face the sites on the thin filament, represented by small rectangular projections. Left S-1 head first attaches to the site on the thin filament, which happened to be in its close vicinity (top), changes its configuration to move the thin filament to the right (arrow, middle), and then detach from the site on the thin filament (bottom). As the result, another site on the thin filament comes in close vicinity of right S-1 head, which then starts the cycle again. Axial spacing of the S-1 heads on the thick filament differs from that of the sites on the thin filament, so that the attachment-detachment cycle takes place asynchronously. Up to the present time, the attachment-detachment cycle shown in Fig.2, still constitutes the framework of most contraction models at the molecular level. The most crucial step of the attachment-detachment cycle is, of course, conformational changes of the S-1 head attached to the thin filament shown in the middle diagram.
eBook - PDFCurrent Basic and Pathological Approaches to the Function of Muscle Cells and Tissues
From Molecules to Humans
- Haruo Sugi(Author)
- 2012(Publication Date)
- IntechOpen(Publisher)
In the middle1950s, H.E. Huxley & Hanson (1954) made a monumental discovery that a skeletal muscle consists of hexagonal lattice of actin and myosin filaments, and that muscle contraction results from relative sliding between actin and myosin filaments (Fig. 6). Figure 6. Electron micrographs of longitudinal thin section of rabbi psoas muscle myofibrils (H.E. Huxley, 1957). Considerable progress has been made with respect to the structure and function of actin and myosin filaments after the discovery of sliding filament mechanism in muscle contraction. As shown in Fig.7A, a myosin molecule is divided into two parts; (1) a long rod called light meromyosin (LMM) and (2) the rest of myosin molecule consisting of a short rod (S2) and two heads (S1) is called heavy meromyosin (HMM). In myosin filaments (or thick fila-ments), LMM aggregates to form filament backbone, which is polarized in opposite direc-tions on either side of the central part. While the S1 heads extend laterally from the filament backbone with an axial interval of 14.3nm (Fig.7B). The central part of myosin filament is called the bare region (or bare zone), where the projection of myosin head is absent. Current Basic and Pathological Approaches to the Function of Muscle Cells and Tissues – From Molecules to Humans 10 Figure 7. Ultrastructure of myosin (thick) and actin (thin) filaments and their arrangement within a sarcomere. (A) Diagram of a myosin molecule. (B) Arrangement of myosin molecules to form a myosin filament. (C) Arrangement of actin monomers (G-actin) in an actin filament. (D) Longitudinal arrange-ment of actin and myosin filaments within a sarcomere. Note that the half sarcomere is the structural and functional unit of muscle (Sugi, 1992). On the other hand, actin filaments consist primarily of two helical strands of globular actin monomers (G-actin) , which are wound around each other with a pitch of 35.5nm. The axial separation of actin monomers in actin filaments is 5.46nm (Fig.7C).
eBook - PDF- Hans-W. Müller-Wohlfahrt, Peter Ueblacker, Lutz Haensel, William E. Garrett Jr., Hans-W. Müller-Wohlfahrt, Peter Ueblacker, Lutz Haensel, William E. Garrett Jr.(Authors)
- 2013(Publication Date)
- Thieme(Publisher)
2 Basic Physiology and Aspects of Exercise B. Brenner, N. Maassen Translated by Terry Telger Basic Physiology 60 Sarcomere, Muscle Force, and Muscle Shortening 60 Basic Principles of Muscular Contraction and Its Regulation 61 Gradation of Muscle Force during Voluntary Movements 66 Types of Muscular Contraction 67 Neuromuscular Control Mechanisms 71 Aspects of Exercise Physiology 77 Types of Muscle Fiber 77 Overview of Muscular Metabolism 78 Warm-Up 81 Fatigue 82 Recovery 86 Training Adaptations 86 Basic Physiology B. Brenner Sarcomere, Muscle Force, and Muscle Shortening Active forces and the shortening of muscle are the result of repetitive, cyclic interactions of myosin molecules with actin filaments. To generate the highest possible forces per cross-sectional area, filaments of actin and myosin form a close-packed arrangement within the basic con-tractile unit of muscle, the sarcomere ( Fig. 2.1a ; see also Figs. 1.16 and 1.18 ). The sarcomere is the segment of a myofibril of muscle fiber located between two adjacent Z disks. Macroscopic forces are generated by the parallel ar-rangement of myofibrils in the muscle fibers and by the parallel arrangement of myriad muscle fibers in a muscle. Numerous sarcomeres are arranged in series (approxi-mately 500 per millimeter of fiber length), so that the mi-croscopic shortening of individual sarcomeres adds up to macroscopic changes in muscle length. Each myosin molecule ( Fig. 2.1b ) is composed of two intertwined heavy chains. Each heavy chain consists of a globular head domain and a threadlike tail. The tails of the two heavy chains are coiled around each other to form the rod of the myosin molecule. Each head domain is associated with two light chains. Several hundred myo-sin molecules associate at their rod parts to form the bipo-lar myosin filaments ( Fig. 2.1c ). Titin molecules are springlike structures associated with the myosin filaments and keep the myosin filaments centered in the sarcomere.
eBook - PDF- Geoffrey H. Bourne(Author)
- 2013(Publication Date)
- Academic Press(Publisher)
6 From Hill (1950). in practice, it is found that, among vertebrates at least, the A filament lengths are all almost identical, even in muscles with very different speeds of shortening. This suggests that some other factor limits the tension that can be sustained by a given pair of thick and thin filaments and makes it imprac-tical to take advantage of higher ATPase activities and higher sliding velocities to afford economies in construction of the kind discussed above. The most likely factor is the strength of the thin filaments them-selves, or of the structure to which they are attached at the point where their polarity is reversed. It is interesting that in the case of muscles with longer A bands (e.g., arthropods) the number of thin filaments 7. Molecular Basis of Contraction 383 associated with each thick filament is also greater so that the tension present in each is reduced, e.g., in the cockroach (Hagopian, 1966). The actual total tension developed will depend, in addition, on the closeness of the filament packing, which in turn depends on how many cross bridges can be packed in per unit area. Muscles are structures with relatively large cross-sectional areas, which suggests that the size of the basic contractile unit cannot readily be reduced. The other details of the band pattern—i.e., the I-filament length and the extent of overlap at rest length—are likely to represent a compromise between a number of conflicting requirements. If the I bands were made longer, then a muscle could shorten further before the Z lines came up against the ends of the A band. It could then be arranged to work at a better mechanical advantage (i.e., attached further away from the fulcrum of the movement), thereby requiring a smaller area of muscle for the same couple, providing that the velocity of shortening was in-creased.
eBook - PDFProgress in Biophysics and Biophysical Chemistry
Progress Series, Volume 7
- J. A. V. Butler, B. Katz(Authors)
- 2016(Publication Date)
- Pergamon(Publisher)
Not enough is known at present about the submicroscopic structure of smooth muscle to make a definite statement either way, but there does not seem to be anything to exclude the possibility that smooth muscle contains, in a much less orderly arrangement, filaments which are moved past one another by a mechanism similar to that pro-posed here for striated muscle. The absence of any marked change in the wide-angle X-ray pattern ( A S T B U R Y , 1 9 4 7 ) and in the strength of the intrinsic component of the birefringence ( F I S C H E R , 1 9 4 4 ) when smooth muscle is stretched or shortened over a wide range, do indeed suggest that the filaments move relative to one another without much internal rearrangement; and as long ago as 1 9 3 6 , B O Z L E R suggested that the mechanical behaviour of smooth muscle could be more easily explained by assuming that contraction took place by relative movement between the molecules, than by changes in their shape. V . O T H E R P H E N O M E N A IN M U S C L E The hypothesis of muscular contraction set out in the preceding sections was originally developed as an attempt to fit together the available information on ( 1 ) muscle structure, ( 2 ) the relationships between shortening, tension and heat liberation, and ( 3 ) the outstanding facts concerning the interactions of actin, myosin and A T P . There are of course many other phenomena which may provide important clues to the mechanism of contraction and which will have to be explained by any theory which aims at completeness. In the following para-graphs, some of these phenomena will be discussed in relation both to the idea that length changes take place by sliding of actin and myosin filaments past one another, and to the particular hypothesis which has been developed here. Possible new interpretations of the data emerge in several cases. M U S C L E S T R U C T U R E A N D T H E O R I E S O F C O N T R A C T I O N 3 0 0 V.
eBook - PDF- Alfred Stracher(Author)
- 2013(Publication Date)
- Academic Press(Publisher)
5h X X X X XX \ x x X ) x * X X *x 2.0 2.2 2.4 2.6 2.8 3.0 5 >jm Fig. 48. Graph showing observed ratios between intensities of the [10] and [11] equa- torial X-ray reflections as a function of the sarcomere length of the muscle: X, resting muscle; · , contracting muslce; 0> muscle in rigor. The ratio decreases—that is, the rela- tive intensity of the [11] reflection becomes greater—as the sarcomere length decreases (greater overlap, hence greater length of actin filament ordered at trigonal points in A- band lattice). The changes in the ratio for different physiological states of the muscle are believed to be associated with lateral cross-bridge movements (see text). (From Haselgrove, 1970.) 1. MOLECULAR BASIS OF CONTRACTION 7 9 Actin a Myosin Myosin Fig. 49. Active change in angle of attachment of cross-bridges (SI subunits) to actin filaments could produce relative sliding movement between filaments maintained at con- stant lateral separation (for small changes in muscle length) by long-range force balance. Bridges can act asynchronously because subunit and helical periodicities differ in the actin and myosin filaments, (a) Left-hand bridge has just attached; other bridge is already partially tilted, (b) Left-hand bridge has just come to end of its working stroke; other bridge has already detached, and will probably not be able to attach to this actin filament again until further sliding brings helically arranged sites on actin into favorable orienta- tion. Mechanism will accommodate itself to changes in filament side-spacing by alterations in tilt of S2. VII. Some Biochemical and Physiological Implications of the Structural Results The model for muscular contraction put forward in this chapter is a very straightforward one, and its general features are fairly generally accepted. Thus it can serve as a useful structural background for many of the topics discussed elsewhere in these volumes.
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