scholarly journals General model of myosin filament structure. III Molecular packing arrangements in myosin filaments

1974 ◽  
Vol 84 (2) ◽  
pp. 374
Keyword(s):  
General Model ◽  
Molecular Packing ◽  
Myosin Filament ◽  
Filament Structure ◽  
Myosin Filaments

scholarly journals Myosin filament structure in vertebrate smooth muscle.

1996 ◽  
Vol 134 (1) ◽  
pp. 53-66 ◽  
Author(s):  
J Q Xu ◽  
B A Harder ◽  
P Uman ◽  
R Craig
Keyword(s):  
Smooth Muscle ◽  
Striated Muscle ◽  
Smooth Muscles ◽  
Helical Structure ◽  
Structure Characteristic ◽  
Myosin Filament ◽  
Filament Structure ◽  
Myosin Filaments ◽  
Intact Muscle

The in vivo structure of the myosin filaments in vertebrate smooth muscle is unknown. Evidence from purified smooth muscle myosin and from some studies of intact smooth muscle suggests that they may have a nonhelical, side-polar arrangement of crossbridges. However, the bipolar, helical structure characteristic of myosin filaments in striated muscle has not been disproved for smooth muscle. We have used EM to investigate this question in a functionally diverse group of smooth muscles (from the vascular, gastrointestinal, reproductive, and visual systems) from mammalian, amphibian, and avian species. Intact muscle under physiological conditions, rapidly frozen and then freeze substituted, shows many myosin filaments with a square backbone in transverse profile. Transverse sections of fixed, chemically skinned muscles also show square backbones and, in addition, reveal projections (crossbridges) on only two opposite sides of the square. Filaments gently isolated from skinned smooth muscles and observed by negative staining show crossbridges with a 14.5-nm repeat projecting in opposite directions on opposite sides of the filament. Such filaments subjected to low ionic strength conditions show bare filament ends and an antiparallel arrangement of myosin tails along the length of the filament. All of these observations are consistent with a side-polar structure and argue against a bipolar, helical crossbridge arrangement. We conclude that myosin filaments in all smooth muscles, regardless of function, are likely to be side-polar. Such a structure could be an important factor in the ability of smooth muscles to contract by large amounts.

Mechanism of partial adaptation in airway smooth muscle after a step change in length

2007 ◽  
Vol 103 (2) ◽  
pp. 569-577 ◽  
Author(s):  
Farah Ali ◽  
Leslie Chin ◽  
Peter D. Paré ◽  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Intermediate State ◽  
Ultrastructural Changes ◽  
Myosin Filament ◽  
Shortening Velocity ◽  
Myosin Filaments ◽  
Partial Adaptation ◽  
Static Conditions

The phenomenon of length adaptation in airway smooth muscle (ASM) is well documented; however, the underlying mechanism is less clear. Evidence to date suggests that the adaptation involves reassembly of contractile filaments, leading to reconfiguration of the actin filament lattice and polymerization or depolymerization of the myosin filaments within the lattice. The time courses for these events are unknown. To gain insights into the adaptation process, we examined ASM mechanical properties and ultrastructural changes during adaptation. Step changes in length were applied to isolated bundles of ASM cells; changes in force, shortening velocity, and myosin filament mass were then quantified. A greater decrease in force was found following an acute decrease in length, compared with that of an acute increase in length. A decrease in myosin filament mass was also found with an acute decrease in length. The shortening velocity measured immediately after the length change was the same as that measured after the muscle had fully adapted to the new length. These observations can be explained by a model in which partial adaptation of the muscle leads to an intermediate state in which reconfiguration of the myofilament lattice occurred rapidly, followed by a relatively slow process of polymerization of myosin filaments within the lattice. The partially adapted intermediate state is perhaps more physiologically relevant than the fully adapted state seen under static conditions, and it simulates a more realistic behavior for ASM in vivo.

scholarly journals Force maintenance and myosin filament assembly regulated by Rho-kinase in airway smooth muscle

2015 ◽  
Vol 308 (1) ◽  
pp. L1-L10 ◽  
Author(s):  
Bo Lan ◽  
Linhong Deng ◽  
Graham M. Donovan ◽  
Leslie Y. M. Chin ◽  
Harley T. Syyong ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Initial Phase ◽  
Rho Kinase ◽  
Myosin Filament ◽  
Second Phase ◽  
Minimal Effect ◽  
Kinase Inhibition ◽  
Myosin Filaments ◽  
Force Maintenance

Smooth muscle contraction can be divided into two phases: the initial contraction determines the amount of developed force and the second phase determines how well the force is maintained. The initial phase is primarily due to activation of actomyosin interaction and is relatively well understood, whereas the second phase remains poorly understood. Force maintenance in the sustained phase can be disrupted by strains applied to the muscle; the strain causes actomyosin cross-bridges to detach and also the cytoskeletal structure to disassemble in a process known as fluidization, for which the underlying mechanism is largely unknown. In the present study we investigated the ability of airway smooth muscle to maintain force after the initial phase of contraction. Specifically, we examined the roles of Rho-kinase and protein kinase C (PKC) in force maintenance. We found that for the same degree of initial force inhibition, Rho-kinase substantially reduced the muscle's ability to sustain force under static conditions, whereas inhibition of PKC had a minimal effect on sustaining force. Under oscillatory strain, Rho-kinase inhibition caused further decline in force, but again, PKC inhibition had a minimal effect. We also found that Rho-kinase inhibition led to a decrease in the myosin filament mass in the muscle cells, suggesting that one of the functions of Rho-kinase is to stabilize myosin filaments. The results also suggest that dissolution of myosin filaments may be one of the mechanisms underlying the phenomenon of fluidization. These findings can shed light on the mechanism underlying deep inspiration induced bronchodilation.

Myosin Filament Structure and Myosin Crossbridge Dynamics in Fish and Insect Muscles

2003 ◽  
pp. 251-266 ◽  
Author(s):  
John M. Squire ◽  
Hind A. AL-Khayat ◽  
Jeffrey J. Harford ◽  
Liam Hudson ◽  
Tom C. Irving ◽  
...  
Keyword(s):  
Myosin Filament ◽  
Filament Structure

scholarly journals Sarcomere-length dependence of myosin filament structure in skeletal muscle fibres of the frog

2014 ◽  
Vol 592 (5) ◽  
pp. 1119-1137 ◽  
Author(s):  
Massimo Reconditi ◽  
Elisabetta Brunello ◽  
Luca Fusi ◽  
Marco Linari ◽  
Manuel Fernandez Martinez ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Sarcomere Length ◽  
Myosin Filament ◽  
Muscle Fibres ◽  
Length Dependence ◽  
Filament Structure ◽  
Skeletal Muscle Fibres

scholarly journals Supercontracted state of vertebrate smooth muscle cell fragments reveals myofilament lengths.

1990 ◽  
Vol 111 (6) ◽  
pp. 2451-2461 ◽  
Author(s):  
J V Small ◽  
M Herzog ◽  
M Barth ◽  
A Draeger
Keyword(s):  
Smooth Muscle ◽  
Actin Filaments ◽  
Cytoskeletal Proteins ◽  
Terminal Phase ◽  
Myosin Filament ◽  
Protein Loss ◽  
Whole Cells ◽  
Myosin Filaments ◽  
Central Bundle ◽  
Cell Fragments

Isolated cell preparations from chicken gizzard smooth muscle typically contain a mixture of cell fragments and whole cells. Both species are spontaneously permeable and may be preloaded with externally applied phalloidin and antibodies and then induced to contract with Mg ATP. Labeling with antibodies revealed that the cell fragments specifically lacked certain cytoskeletal proteins (vinculin, filamin) and were depleted to various degrees in others (desmin, alpha-actinin). The cell fragments showed a unique mode of supercontraction that involved the protrusion of actin filaments through the cell surface during the terminal phase of shortening. In the presence of dextran, to minimize protein loss, the supercontracted products were star-like in form, comprising long actin bundles radiating in all directions from a central core containing myosin, desmin, and alpha-actinin. It is concluded that supercontraction is facilitated by an effective uncoupling of the contractile apparatus from the cytoskeleton, due to partial degradation of the latter, which allows unhindered sliding of actin over myosin. Homogenization of the cell fragments before or after supercontraction produced linear bipolar dimer structures composed of two oppositely polarized bundles of actin flanking a central bundle of myosin filaments. Actin filaments were shown to extend the whole length of the bundles and their length averaged integral to 4.5 microns. Myosin filaments in the supercontracted dimers averaged 1.6 microns in length. The results, showing for the first time the high actin to myosin filament length ratio in smooth muscle are readily consistent with the slow speed of shortening of this tissue. Other implications of the results are also discussed.

scholarly journals Filament evanescence of myosin II and smooth muscle function

2021 ◽  
Vol 153 (3) ◽  
Author(s):  
Lu Wang ◽  
Pasquale Chitano ◽  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Muscle Function ◽  
Molecular Mechanisms ◽  
Striated Muscle ◽  
Myosin Ii ◽  
Length Distribution ◽  
Myosin Filament ◽  
New Paradigm ◽  
Smooth Muscle Function ◽  
Myosin Filaments

Smooth muscle is an integral part of hollow organs. Many of them are constantly subjected to mechanical forces that alter organ shape and modify the properties of smooth muscle. To understand the molecular mechanisms underlying smooth muscle function in its dynamic mechanical environment, a new paradigm has emerged that depicts evanescence of myosin filaments as a key mechanism for the muscle’s adaptation to external forces in order to maintain optimal contractility. Unlike the bipolar myosin filaments of striated muscle, the side-polar filaments of smooth muscle appear to be less stable, capable of changing their lengths through polymerization and depolymerization (i.e., evanescence). In this review, we summarize accumulated knowledge on the structure and mechanism of filament formation of myosin II and on the influence of ionic strength, pH, ATP, myosin regulatory light chain phosphorylation, and mechanical perturbation on myosin filament stability. We discuss the scenario of intracellular pools of monomeric and filamentous myosin, length distribution of myosin filaments, and the regulatory mechanisms of filament lability in contraction and relaxation of smooth muscle. Based on recent findings, we suggest that filament evanescence is one of the fundamental mechanisms underlying smooth muscle’s ability to adapt to the external environment and maintain optimal function. Finally, we briefly discuss how increased ROCK protein expression in asthma may lead to altered myosin filament stability, which may explain the lack of deep-inspiration–induced bronchodilation and bronchoprotection in asthma.

A Theoretical Assessment of the Influence of Myosin Filament Dispersion on Smooth Muscle Contraction

2011 ◽  
Author(s):  
Martin Kroon
Keyword(s):  
Smooth Muscle ◽  
Constitutive Model ◽  
Muscle Tissue ◽  
Strain Energy Function ◽  
Smooth Muscle Contraction ◽  
Myosin Filament ◽  
Smooth Muscle Tissue ◽  
Active Stress ◽  
Biomechanical Behavior ◽  
Myosin Filaments

A new constitutive model for the biomechanical behavior of smooth muscle tissue is employed to investigate the influence of statistical dispersion in the orientation of myosin filaments. The number of activated cross-bridges between the actin and myosin filaments governs the contractile force generated by the muscle and also the contraction speed. A strain-energy function is used to describe the mechanical behavior of the smooth muscle tissue. The predictions from the constitutive model are compared to histological and isometric tensile test results for smooth muscle tissue from swine carotid artery. In order to be able to predict the active stress at different muscle lengths, a filament dispersion significantly larger than the one observed experimentally was required. Furthermore, a comparison of the predicted active stress for a case of uniaxially oriented myosin filaments and a case of filaments with a dispersion based on the experimental histological data shows that the difference in generated stress is noticeable but limited. Thus, the results suggest that myosin filament dispersion alone cannot explain the increase in active muscle stress with increasing muscle stretch.

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