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 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.

scholarly journals Myosin filament assembly in an ever-changing myofilament lattice of smooth muscle

2005 ◽  
Vol 289 (6) ◽  
pp. C1363-C1368 ◽  
Author(s):  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Thick Filament ◽  
Myosin Filament ◽  
Major Development ◽  
Wide Range ◽  
Myosin Filaments ◽  
New Perspective ◽  
The Right ◽  
Open Question

A major development in smooth muscle research in recent years is the recognition that the myofilament lattice of the muscle is malleable. The malleability appears to stem from plastic rearrangement of contractile and cytoskeletal filaments in response to stress and strain exerted on the muscle cell, and it allows the muscle to adapt to a wide range of cell lengths and maintain optimal contractility. Although much is still poorly understood, we have begun to comprehend some of the basic mechanisms underlying the assembly and disassembly of contractile and cytoskeletal filaments in smooth muscle during the process of adaptation to large changes in cell geometry. One factor that likely facilitates the plastic length adaptation is the ability of myosin filaments to form and dissolve at the right place and the right time within the myofilament lattice. It is proposed herein that formation of myosin filaments in vivo is aided by the various filament-stabilizing proteins, such as caldesmon, and that the thick filament length is determined by the dimension of the actin filament lattice. It is still an open question as to how the dimension of the dynamic filament lattice is regulated. In light of the new perspective of malleable myofilament lattice in smooth muscle, the roles of many smooth muscle proteins could be assigned or reassigned in the context of plastic reorganization of the contractile apparatus and cytoskeleton.

scholarly journals An invertebrate smooth muscle with striated muscle myosin filaments

2015 ◽  
Vol 112 (42) ◽  
pp. E5660-E5668 ◽  
Author(s):  
Guidenn Sulbarán ◽  
Lorenzo Alamo ◽  
Antonio Pinto ◽  
Gustavo Márquez ◽  
Franklin Méndez ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Actin Filaments ◽  
Striated Muscle ◽  
Smooth Muscles ◽  
Structural Similarity ◽  
Striated Muscles ◽  
Muscle Tissues ◽  
Myosin Filaments ◽  
Muscle Myosin ◽  
Surprising Finding

Muscle tissues are classically divided into two major types, depending on the presence or absence of striations. In striated muscles, the actin filaments are anchored at Z-lines and the myosin and actin filaments are in register, whereas in smooth muscles, the actin filaments are attached to dense bodies and the myosin and actin filaments are out of register. The structure of the filaments in smooth muscles is also different from that in striated muscles. Here we have studied the structure of myosin filaments from the smooth muscles of the human parasite Schistosoma mansoni. We find, surprisingly, that they are indistinguishable from those in an arthropod striated muscle. This structural similarity is supported by sequence comparison between the schistosome myosin II heavy chain and known striated muscle myosins. In contrast, the actin filaments of schistosomes are similar to those of smooth muscles, lacking troponin-dependent regulation. We conclude that schistosome muscles are hybrids, containing striated muscle-like myosin filaments and smooth muscle-like actin filaments in a smooth muscle architecture. This surprising finding has broad significance for understanding how muscles are built and how they evolved, and challenges the paradigm that smooth and striated muscles always have distinctly different components.

Studies on isolated smooth muscle cells: The contractile apparatus

1977 ◽  
Vol 24 (1) ◽  
pp. 327-349
Author(s):  
J.V. Small
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Maximum Velocity ◽  
Muscle Cells ◽  
Myosin Filament ◽  
Contractile Apparatus ◽  
Myosin Filaments ◽  
Intact Muscle ◽  
10 Nm Filaments ◽  
Triton X

Smooth muscle cells may be isolated from the taenia coli muscle of the guinea pig which, when made permeable by treatment with Triton X-100 (0-05%) show a sensitivity to Ca for contraction with MgATP. The rate of contraction, about 10 micron s-1, corresponds closely to the maximum velocity of shortening of the intact muscle. Electron microscopy of such partially demembranated muscle cells shows that myosin filaments of about 16-nm diameter are present in both the rigor and the relaxes states. In addition, the actin and myosin filaments are commonly seen to be associated in groups corresponding approximately in size to the fibrils recognizable in cells in rigor in the light microscope. The dense bodies and the 10-nm filaments are found located between the actin-myosin filament groups. The thick myosin filaments may be isolated by fragmentation of the cells under relaxing conditions. These native filaments range up to about 8 micron in length and show the same structural organization as filaments aseembled from purified smooth muscle myosin: there is no central bare zone and bare edges, about 0-2 micrin long, occur at the filament ends. The lack of bipolarity of the native smooth muscle muosin filaments and the absence, in the contractile apparatus, of actin-associated structures equivalent to Z-lines suggests that the amount of shearing that can occur between the actin and myosin filaments is considerably greater than in skeletal muscle.

scholarly journals Aging-associated changes in microRNA expression profile of internal anal sphincter smooth muscle: Role of microRNA-133a

2016 ◽  
Vol 311 (5) ◽  
pp. G964-G973 ◽  
Author(s):  
Jagmohan Singh ◽  
Ettickan Boopathi ◽  
Sankar Addya ◽  
Benjamin Phillips ◽  
Isidore Rigoutsos ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Anal Sphincter ◽  
Internal Anal Sphincter ◽  
Smooth Muscles ◽  
Smooth Muscle Contractility ◽  
Network Analyses ◽  
Rhoa Signaling

A comprehensive genomic and proteomic, computational, and physiological approach was employed to examine the (previously unexplored) role of microRNAs (miRNAs) as regulators of internal anal sphincter (IAS) smooth muscle contractile phenotype and basal tone. miRNA profiling, genome-wide expression, validation, and network analyses were employed to assess changes in mRNA and miRNA expression in IAS smooth muscles from young vs. aging rats. Multiple miRNAs, including rno-miR-1, rno-miR-340-5p, rno-miR-185, rno-miR-199a-3p, rno-miR-200c, rno-miR-200b, rno-miR-31, rno-miR-133a, and rno-miR-206, were found to be upregulated in aging IAS. qPCR confirmed the upregulated expression of these miRNAs and downregulation of multiple, predicted targets ( Eln, Col3a1, Col1a1, Zeb2, Myocd, Srf, Smad1, Smad2, Rhoa/Rock2, Fn1, Tagln v2, Klf4, and Acta2) involved in regulation of smooth muscle contractility. Subsequent studies demonstrated an aging-associated increase in the expression of miR-133a, corresponding decreases in RhoA, ROCK2, MYOCD, SRF, and SM22α protein expression, RhoA-signaling, and a decrease in basal and agonist [U-46619 (thromboxane A2analog)]-induced increase in the IAS tone. Moreover, in vitro transfection of miR-133a caused a dose-dependent increase of IAS tone in strips, which was reversed by anti-miR-133a. Last, in vivo perianal injection of anti-miR-133a reversed the loss of IAS tone associated with age. This work establishes the important regulatory effect of miRNA-133a on basal and agonist-stimulated IAS tone. Moreover, reversal of age-associated loss of tone via anti-miR delivery strongly implicates miR dysregulation as a causal factor in the aging-associated decrease in IAS tone and suggests that miR-133a is a feasible therapeutic target in aging-associated rectoanal incontinence.

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.

Filament Formation by Slime Mould Myosin Isolated at Low Ionic Strength

1974 ◽  
Vol 15 (1) ◽  
pp. 113-129
Author(s):  
H. HINSSEN ◽  
J. D'HAESE
Keyword(s):  
Ionic Strength ◽  
Striated Muscle ◽  
Divalent Cations ◽  
Filament Formation ◽  
Selective Precipitation ◽  
Slime Mould ◽  
Preparation Conditions ◽  
Filament Structure ◽  
Low Ionic Strength

Myosin was isolated and purified from plasmodia of the slime mould Physarum polycephalum by a new method. This method is based on actomyosin extraction at low ionic strength after extensive washing, followed by the selective precipitation of myosin at pH 6.1 under relaxing conditions. The yield of myosin was 3-5 times higher than reported for other methods. In contrast to earlier studies a remarkably strong tendency to filament formation was found for slime mould myosin, probably due to a better preservation of some structural properties during preparation. Conditions were worked out under which numerous filaments up to 4 µm in length can be produced. It was established that not only a gradual decrease of ionic strength may influence filament formation, but also pH, ATP concentration and the presence of divalent cations. Compared to the current filament models a difference exists in the structure of the filaments. No central bare zone can be found, and thus, they lack an apparent bipolarity. Along the entire filament there are lateral projections representing the head portion of myosin molecules. A clear periodicity with an axial repeat of about 14 nm was observed, indicating a highly ordered arrangement of these projections. In this paper it is shown for the first time that myosin from one of the primitive motile systems is able to form aggregates of high structural order, indicating that the contraction of non-muscular actomyosin systems is not necessarily effected with oligomeric or randomly aggregated myosin. The possible role of myosin aggregation in vivo and the similarity of filament structure to that recently reported for myosin from vertebrate smooth muscle and striated muscle are discussed.

Activation of MAP kinases in airway smooth muscle

1997 ◽  
Vol 272 (2) ◽  
pp. L244-L252 ◽  
Author(s):  
W. T. Gerthoffer ◽  
I. A. Yamboliev ◽  
J. Pohl ◽  
R. Haynes ◽  
S. Dang ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Map Kinase ◽  
Airway Smooth Muscle ◽  
Map Kinases ◽  
Sodium Dodecyl ◽  
Western Blots ◽  
Mitogen Activated Protein ◽  
Intact Muscle ◽  
Triton X

To test the hypothesis that mitogen-activated protein (MAP) kinases are activated by contractile agonists in intact nonproliferating airway smooth muscle, kinase activities were compared in resting and stimulated canine tracheal smooth muscle. Kinase activities in sodium dodecyl sulfate extracts were assayed by a gel renaturation method. Myelin basic protein kinase activities corresponding to ERK1 and ERK2 immunoreactive proteins were activated twofold above the basal level within 5 min by 1 microM carbachol. MAP kinase activity assayed in crude homogenates using a synthetic peptide substrate (APRTPGGRR) also increased twofold above basal in muscles stimulated with 1 microM carbachol. Two protein kinases separated by Mono-Q chromatography were identified on Western blots as ERK1 and ERK2 MAP kinases. Carbachol stimulation increased caldesmon phosphorylation in intact muscle, and purified caldesmon was a substrate for activated murine ERK2 MAP kinase. Activated ERK2 MAP kinase added to Triton X-100-permeabilized fibers potentiated Ca2+-induced contraction. The results show that ERK MAP kinases are activated after stimulation of muscarinic receptors in airway smooth muscle, which is consistent with coupling of MAP kinases to phosphorylation of caldesmon in vivo.

The Sarcoplasmic Reticulum of Smooth Muscle Fibers

1982 ◽  
Vol 37 (5-6) ◽  
pp. 481-488 ◽  
Author(s):  
L. Raeymaekers
Keyword(s):  
Smooth Muscle ◽  
Calcium Oxalate ◽  
Striated Muscle ◽  
Smooth Muscles ◽  
Morphological Characterization ◽  
Calcium Oxalate Crystals ◽  
Additional Amount ◽  
Skinned Smooth Muscle ◽  
Ca Uptake

Abstract The ability of the sarcoplasmic (endoplasmic) reticulum (SR, ER) of smooth muscle cells to accumulate Ca was demonstrated by measuring the uptake of 45Ca in fibers which were chemically skinned with saponin, and by electron cytochemistry of the accumulated Ca. The Ca uptake was dependent on ATP and it was stimulated by oxalate, as it is the case in SR of striated muscle. Electron microscopy of the skinned smooth muscle preparations revealed the presence of calcium oxalate deposits in the reticulum. The SR vesicles were isolated from several smooth muscles. The purification was carried out by taking advantage of the density increase of the SR vesicles after loading with calcium in the presence of oxalate. Among the muscles investigated the smooth muscle of the pig stomach was found to be the most suitable and it was selected for further biochemical and morphological characterization of the SR vesicles. These vesicles, which contain calcium oxalate crystals, were able to accumulate an additional amount of Ca. The Ca uptake was supported by several energy yielding substrates. Their order of potency was ATP > dATP ≃ UTP > ITP > GTP ≃ CTP. The rate of Ca uptake was two orders of magnitude slower than that in SR of skeletal muscle. The measurement of the level of phosphorylated Ca transport intermediate showed that this difference is due to smaller number of calcium transport sites per vesicle. The distribution of intramembrane particles in freeze-fractured specimens is in agreement with this conclusion.

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