scholarly journals THE DOUBLE ARRAY OF FILAMENTS IN CROSS-STRIATED MUSCLE

1957 ◽  
Vol 3 (5) ◽  
pp. 631-648 ◽  
Author(s):  
H. E. Huxley
Keyword(s):  
Striated Muscle ◽  
The Other ◽  
Thin Sections ◽  
Alternative Models ◽  
Double Array ◽  
The Cross ◽  
Cross Bridges

The conditions under which one might expect to see the secondary filaments (if they exist) in longitudinal sections of striated muscle, are discussed. It is shown that these conditions were not satisfied in previously published works for the sections were too thick. When suitably thin sections are examined, the secondary filaments can be seen perfectly easily. It is also possible to see clearly other details of the structure, notably the cross-bridges between primary and secondary filaments, and the tapering of the primary filaments at their ends. The arrangement of the filaments and the changes associated with contraction and with stretch are identical to those already deduced from previous observations and described in terms of the interdigitating filament model in previous papers. There are therefore excellent grounds for believing that this model is correct. The alternative models which have been proposed appear to be incompatible both with the present observations and with much of the other available evidence.

scholarly journals Different structural states of a microtubule cross-linking molecule, captured by quick-freezing motile axostyles in protozoa.

1986 ◽  
Vol 103 (6) ◽  
pp. 2209-2227 ◽  
Author(s):  
J E Heuser
Keyword(s):  
Active Role ◽  
Longitudinal Shear ◽  
The Other ◽  
Cross Bridge ◽  
Other Hand ◽  
Quick Freezing ◽  
Cross Links ◽  
Dynein Arms ◽  
The Cross ◽  
Cross Bridges

Freeze-etch preparation of the laminated bundles of microtubules in motile axostyles demonstrates that the cross-bridges populating individual layers or laminae are structurally similar to the dynein arms of cilia and flagellae. Also, like dynein, they are extracted by high salt and undergo a change in tilt upon removal of endogenous ATP (while the axostyle as a whole straightens and becomes stiff). On the other hand, the bridges running between adjacent microtubule laminae in the axostyle turn out to be much more delicate and wispy in appearance, and display no similarity to dynein arms. Thus we propose that the internal or "intra-laminar" cross-bridges are the active force-generating ATPases in this system, and that they generate overall bends or changes in the helical pitch of the axostyle by altering the longitudinal and lateral register of microtubules in each lamina individually; e.g., by "warping" each lamina and creating longitudinal shear forces within it. The cross-links between adjacent laminae, on the other hand, would then simply be force-transmitting elements that serve to translate the shearing forces generated within individual laminae into overall helical shape changes. (This hypothesis differs from the views of earlier workers who considered a more active role for the later cross-links, postulating that they cause an active sliding between adjacent layers that somehow leads to axostyle movement.) Also described here are physical connections between adjacent intra-laminar cross-bridges, structurally analogous to the overlapping components of the outer dynein arms of cilia and flagella. As with dynein, these may represent a mechanism for propagating local changes from cross-bridge to cross-bridge down the axostyle, as occurs during the passage of bends down the length of the organelle.

scholarly journals Evidence from Insect Fibrillar Muscle about the Elementary Contractile Process

1967 ◽  
Vol 50 (6) ◽  
pp. 139-156 ◽  
Author(s):  
J. W. S. Pringle
Keyword(s):  
Ionic Strength ◽  
Atpase Activity ◽  
Striated Muscle ◽  
Contractile Activity ◽  
High Elasticity ◽  
Flight Muscles ◽  
The Cross ◽  
Cross Bridges ◽  
Low Ionic Strength ◽  
Water Bugs

Bundles of myofibrils prepared from the dorsal longitudinal flight muscles of giant water bugs show oscillatory contractile activity in solutions of low ionic strength containing ATP and 10-8-10-7 M Ca2+. This is due to delay between changes of length and changes of tension under activating conditions. The peculiarities of insect fibrillar muscle which give rise to this behavior are (1) the high elasticity of relaxed myofibrils, (2) a smaller degree of Ca2+ activation of ATPase activity in unstretched myofibrils and extracted actomyosin, and (3) a direct effect of stretch on ATPase activity. It is shown that the cross-bridges of striated muscle are probably formed from the heads of three myosin molecules and that in insect fibrillar muscle the cycles of mechanochemical energy conversion in the cross-bridges can be synchronized by imposed changes of length. This material is more suitable than vertebrate striated muscle for a study of the nature of the elementary contractile process.

scholarly journals Structural changes induced in Ca2+-regulated myosin filaments by Ca2+ and ATP.

1989 ◽  
Vol 109 (2) ◽  
pp. 529-538 ◽  
Author(s):  
L L Frado ◽  
R Craig
Keyword(s):  
Structural Changes ◽  
Striated Muscle ◽  
Structural Basis ◽  
Ordered Structure ◽  
Compact Structure ◽  
Crude Homogenate ◽  
Myosin Filaments ◽  
The Cross ◽  
Cross Bridges ◽  
Muscle Myosin

We have used electron microscopy and proteolytic susceptibility to study the structural basis of myosin-linked regulation in synthetic filaments of scallop striated muscle myosin. Using papain as a probe of the structure of the head-rod junction, we find that this region of myosin is approximately five times more susceptible to proteolytic attack under activating (ATP/high Ca2+) or rigor (no ATP) conditions than under relaxing conditions (ATP/low Ca2+). A similar result was obtained with native myosin filaments in a crude homogenate of scallop muscle. Proteolytic susceptibility under conditions in which ADP or adenosine 5'-(beta, gamma-imidotriphosphate) (AMPPNP) replaced ATP was similar to that in the absence of nucleotide. Synthetic myosin filaments negatively stained under relaxing conditions showed a compact structure, in which the myosin cross-bridges were close to the filament backbone and well ordered, with a clear 14.5-nm axial repeat. Under activating or rigor conditions, the cross-bridges became clumped and disordered and frequently projected further from the filament backbone, as has been found with native filaments; when ADP or AMPPNP replaced ATP, the cross-bridges were also disordered. We conclude (a) that Ca2+ and ATP affect the affinity of the myosin cross-bridges for the filament backbone or for each other; (b) that the changes observed in the myosin filaments reflect a property of the myosin molecules alone, and are unlikely to be an artifact of negative staining; and (c) that the ordered structure occurs only in the relaxed state, requiring both the presence of hydrolyzed ATP on the myosin heads and the absence of Ca2+.

Ultrastructure of the caudal muscle cells in the larva of a polyclinid ascidian

1985 ◽  
Vol 63 (6) ◽  
pp. 1410-1419 ◽  
Author(s):  
Michael J. Cavey ◽  
Harvey D. Strecker
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Striated Muscle ◽  
Muscle Cells ◽  
The Other ◽  
The Cross

Two paraxial bands of somatic striated muscle occur in the tail of the larva of the compound ascidian Aplidium ?constellatum. The mononucleate muscle cells of each band align in longitudinal rows between the epidermis and the notochord. The cross-striated myofibrils, originating and terminating at intermediate junctions on the transverse cellular boundaries, are indiscrete. They follow a spiral course through the subcortical and medullary sarcoplasm, bypassing the nucleus and the other organelles and inclusions in the center of the cell. Cisternae of the sarcoplasmic reticulum envelop the myofibrils, forming compact fenestrated sheets that are continuous between the sarcomeres and locally undifferentiated with respect to the myofibrillar striations. Cisternae of the perifibrillar sarcoplasmic reticulum near each sarcomeric Z-line establish dyadic interior couplings with a network of tubular invaginations of the sarcolemma. The sarcolemmal tubules can originate from any surface, including the transverse cellular boundaries. Near the half I-bands of the terminal sarcomeres at the intermediate junctions, the perifibrillar cisternae frequently leave the fenestrated sheets and extend to the overlying sarcolemma, becoming the sub-sarcolemmal cisternae of dyadic peripheral couplings.

scholarly journals Myosin Cross-Bridge Behaviour in Contracting Muscle—The T1 Curve of Huxley and Simmons (1971) Revisited

2019 ◽  
Vol 20 (19) ◽  
pp. 4892 ◽  
Author(s):  
Knupp ◽  
Squire
Keyword(s):  
Actin Filaments ◽  
Striated Muscle ◽  
Reliable Estimate ◽  
X Ray Diffraction ◽  
Step Size ◽  
X Ray ◽  
Cross Bridge ◽  
Length Changes ◽  
The Cross ◽  
Cross Bridges

The stiffness of the myosin cross-bridges is a key factor in analysing possible scenarios to explain myosin head changes during force generation in active muscles. The seminal study of Huxley and Simmons (1971: Nature 233: 533) suggested that most of the observed half-sarcomere instantaneous compliance (=1/stiffness) resides in the myosin heads. They showed with a so-called T1 plot that, after a very fast release, the half-sarcomere tension reduced to zero after a step size of about 60Å (later with improved experiments reduced to 40Å). However, later X-ray diffraction studies showed that myosin and actin filaments themselves stretch slightly under tension, which means that most (at least two-thirds) of the half sarcomere compliance comes from the filaments and not from cross-bridges. Here we have used a different approach, namely to model the compliances in a virtual half sarcomere structure in silico. We confirm that the T1 curve comes almost entirely from length changes in the myosin and actin filaments, because the calculated cross-bridge stiffness (probably greater than 0.4 pN/Å) is higher than previous studies have suggested. Our model demonstrates that the formulations produced by previous authors give very similar results to our model if the same starting parameters are used. However, we find that it is necessary to model the X-ray diffraction data as well as mechanics data to get a reliable estimate of the cross-bridge stiffness. In the light of the high cross-bridge stiffness found in the present study, we present a plausible modified scenario to describe aspects of the myosin cross-bridge cycle in active muscle. In particular, we suggest that, apart from the filament compliances, most of the cross-bridge contribution to the instantaneous T1 response may come from weakly-bound myosin heads, not myosin heads in strongly attached states. The strongly attached heads would still contribute to the T1 curve, but only in a very minor way, with a stiffness that we postulate could be around 0.1 pN/Å, a value which would generate a working stroke close to 100 Å from the hydrolysis of one ATP molecule. The new model can serve as a tool to calculate sarcomere elastic properties for any vertebrate striated muscle once various parameters have been determined (e.g., tension, T1 intercept, temperature, X-ray diffraction spacing results).

scholarly journals Actin filaments, stereocilia, and hair cells of the bird cochlea. II. Packing of actin filaments in the stereocilia and in the cuticular plate and what happens to the organization when the stereocilia are bent.

1983 ◽  
Vol 96 (3) ◽  
pp. 822-834 ◽  
Author(s):  
L G Tilney ◽  
E H Egelman ◽  
D J DeRosier ◽  
J C Saunder
Keyword(s):  
Actin Filament ◽  
Hair Cells ◽  
Actin Filaments ◽  
Fine Tuning ◽  
Thin Sections ◽  
The Cross ◽  
Diffraction Patterns ◽  
Cross Bridges ◽  
Different Parts ◽  
Filament Bundle

A comparison of hair cells from different parts of the cochlea reveals the same organization of actin filaments; the elements that vary are the length and number of the filaments. Thin sections of stereocilia reveal that the actin filaments are hexagonally packed and from diffraction patterns of these sections we found that the actin filaments are aligned such that the crossover points of adjacent actin filaments are in register. As a result, the cross-bridges that connect adjacent actin filaments are easily seen in longitudinal sections. The cross-bridges appear as regularly spaced bands that are perpendicular to the axis of the stereocilium. Particularly interesting is that, unlike what one might predict, when a stereocilium is bent or displaced, as might occur during stimulation by sound, the actin filaments are not compressed or stretched but slide past one another so that the bridges become tilted relative to the long axis of the actin filament bundle. In the images of bent bundles, the bands of cross-bridges are then tilted off perpendicular to the stereocilium axis. When the stereocilium is bent at its base, all cross-bridges in the stereocilium are affected. Thus, resistance to bending or displacement must be property of the number of bridges present, which in turn is a function of the number of actin filaments present and their respective lengths. Since hair cells in different parts of the cochlea have stereocilia of different, yet predictable lengths and widths, this means that the force needed to displace the stereocilia of hair cells located at different regions of the cochlea will not be the same. This suggests that fine tuning of the hair cells must be a built-in property of the stereocilia. Perhaps its physiological vulnerability may result from changes of stereociliary structure.

scholarly journals Recent X-ray Diffraction and Electron Microscope Studies of Striated Muscle

1967 ◽  
Vol 50 (6) ◽  
pp. 71-83 ◽  
Author(s):  
H. E. Huxley
Keyword(s):  
Active Sites ◽  
Striated Muscle ◽  
Structural Features ◽  
Actin Binding ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thick Filaments ◽  
Myosin Filaments ◽  
The Cross ◽  
Cross Bridges

The sliding filament model for muscular contraction supposes that an appropriately directed force is developed between the actin and myosin filaments by some process in which the cross-bridges are involved. The cross-bridges between the filaments are believed to represent the parts of the myosin molecules which possess the active sites for ATPase activity and actin-binding ability, and project out sidewise from the backbone of the thick filaments. The arrangement of the cross-bridges is now being studied by improved low-angle X-ray diffraction techniques, which show that in a resting muscle, they are arranged approximately but not exactly in a helical pattern, and that there are other structural features of the thick filaments which give rise to additional long periodicities shown up by the X-ray diagram. The actin filaments also contain helically arranged subunits, and both the subunit repeat and the helical repeat are different from those in the myosin filaments. Diffraction diagrams can be obtained from muscles in rigor (when permanent attachment of the cross-bridges to the actin subunits takes place) and now, taking advantage of the great increase in the speed of recording, from actively contracting muscles. These show that changes in the arrangement of the cross-bridges are produced under both these conditions and are no doubt associated in contraction with the development of force. Thus configurational changes of the myosin component in muscle have been demonstrated: these take place without any significant over-all change in the length of the filaments.

Structural arrangements and the contraction mechanism in striated muscle

1964 ◽  
Vol 160 (981) ◽  
pp. 442-448 ◽  
Keyword(s):  
Striated Muscle ◽  
Molecular Properties ◽  
The Other ◽  
Thin Filaments ◽  
Contractile Mechanism ◽  
Thick Filaments ◽  
Contraction Mechanism ◽  
Ordered Array ◽  
Cross Bridges ◽  
Contractile Structure

This review will try to summarize our present conclusions concerning the contractile structure of striated muscle, based on all the evidence, old and new. We have been attempting to give as detailed and as definite a picture of the contractile mechanism as possible, and to specify what properties it must have, what properties it can have, and what properties it does not have. The more concisely we can do this, the more able we will be to design suitable experiments to distinguish between the remaining possibilities for the detailed molecular properties and events involved in contraction, which still remain almost entirely unknown. The ‘double array of filaments’ model for striated muscle, as it was originally propounded (Hanson & Huxley 1953), has remained essentially unchanged. According to this model, the A -bands contain an ordered array of 100 Å diameter filaments, spaced about 450 Å apart and containing myosin, with each filament continuous from one end of the A -band to the other. A second array of thinner filaments, containing actin, extends on either side of the Z -line, through the I -bands and into the A -bands, interdigitating with the array of thick filaments and terminating at the edges of the H -zones. Cross-bridges extend between the thick and thin filaments in the region of overlap.

Mechanics of tonus fibers of frog muscle

1987 ◽  
Vol 253 (4) ◽  
pp. C599-C606 ◽  
Author(s):  
E. Bozler
Keyword(s):  
Striated Muscle ◽  
Metabolic Effects ◽  
Second Phase ◽  
Sustained Activity ◽  
Strong Stimulation ◽  
Length Changes ◽  
The Cross ◽  
Cross Bridges ◽  
Two Phases ◽  
Fenn Effect

Contractions with two phases of relaxation are induced by brief strong stimulation in some frog muscles. The first phase with rapid relaxation is produced by the twitch fibers; the second phase, which is very slow and is only present after strong stimulation, represents the relaxation of the tonus fibers. At moderate loads, half time of isotonic relaxation of these fibers is as long as 30 min at 2 degrees C, but the rate varies with the load and depends on the condition of the frogs. With regard to the rate of relaxation, the tonus fibers resemble molluscan catch muscles. In tonus fibers, rapid isotonic and isometric relaxation can be induced by a small extension; shortening opposes this effect. These responses are like the length responses previously found in various types of striated muscle. They go in the same direction as the well-known metabolic effects of length changes (Fenn effect). After a large extension by an increase in load there is no active shortening when the load is returned to the previous value. This and other observations show that the slowness of relaxation is not due to sustained activity, but is determined by the strength of the contractile bonds formed during contraction. Because activity during relaxation is very low, it is unlikely that length responses are caused by a modification of the cross-bridge cycle. It is suggested that length changes act through a mechanism that is separate from that initiating contraction, but alters the speed of relaxation by making the cross bridges weaker or stronger.

A New Approach to the Demonstration of Oxidase-Localization Using Tannic Acid Or Catechin

1973 ◽  
Vol 31 ◽  
pp. 698-699
Author(s):  
V. Mizuhira ◽  
Y. Futaesaku
Keyword(s):  
Cross Section ◽  
Tannic Acid ◽  
Elastic Fiber ◽  
The Other ◽  
New Approach ◽  
Tissue Block ◽  
Active Reaction ◽  
The Cross

Previously we reported that tannic acid is a very effective fixative for proteins including polypeptides. Especially, in the cross section of microtubules, thirteen submits in A-tubule and eleven in B-tubule could be observed very clearly. An elastic fiber could be demonstrated very clearly, as an electron opaque, homogeneous fiber. However, tannic acid did not penetrate into the deep portion of the tissue-block. So we tried Catechin. This shows almost the same chemical natures as that of proteins, as tannic acid. Moreover, we thought that catechin should have two active-reaction sites, one is phenol,and the other is catechole. Catechole site should react with osmium, to make Os- black. Phenol-site should react with peroxidase existing perhydroxide.

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