Filament lattice changes in smooth muscle assessed using birefringence

2005 ◽  
Vol 83 (10) ◽  
pp. 933-940 ◽  
Author(s):  
A V Smolensky ◽  
L E Ford
Keyword(s):  
Smooth Muscle ◽  
Time Course ◽  
Structural Changes ◽  
Thick Filament ◽  
Myosin Filament ◽  
Filament Formation ◽  
Tension Development ◽  
Thick Filaments ◽  
Contractile Parameters ◽  
In Series

The long functional range of some types of smooth muscle has been the subject of recent study. It has been proposed that the muscle filament lattice adapts to longer lengths by placing more filaments in series and that lattice plasticity is facilitated by myosin filament evanescence, with filaments dissociating during relaxation and reforming upon activation. Support for these dynamic changes in the filament lattice has been provided partly by changes in contractile parameters at different times in the contraction–relaxation cycle at different lengths. If the changes in contractile parameters result from filament formation and dissociation, these structural changes must occur on the time scale of tension development and relaxation. To assess whether thick-filament formation could account for the contractile changes, we measured birefringence continuously during activation and relaxation and compared these optical changes with the time course of force development and relaxation. Birefringence is a well-known property of muscle; striations in skeletal and cardiac muscle result from the A-bands being anisotropic, i.e., birefringent, and it is now known that this optical property is due to the presence of myosin thick filaments in the A-bands. Thus, the strength of birefringence is expected to represent the density of thick filaments. Here, we describe the principle of the method, the techniques for recording the optical signals, some initial results, and discuss the interpretation of results and some limitations of the method.Key words: airway smooth muscle, myosin filament, plasticity.

Myosin thick filament lability induced by mechanical strain in airway smooth muscle

2001 ◽  
Vol 90 (5) ◽  
pp. 1811-1816 ◽  
Author(s):  
Kuo-Hsing Kuo ◽  
Lu Wang ◽  
Peter D. Paré ◽  
Lincoln E. Ford ◽  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Cross Sections ◽  
Structural Changes ◽  
Isometric Force ◽  
Mechanical Strain ◽  
Thick Filament ◽  
Functional Changes ◽  
Thick Filaments ◽  
Length Changes

Airway smooth muscle adapts to different lengths with functional changes that suggest plastic alterations in the filament lattice. To look for structural changes that might be associated with this plasticity, we studied the relationship between isometric force generation and myosin thick filament density in cell cross sections, measured by electron microscope, after length oscillations applied to the relaxed porcine trachealis muscle. Muscles were stimulated regularly for 12 s every 5 min. Between two stimulations, the muscles were submitted to repeated passive ±30% length changes. This caused tetanic force and thick-filament density to fall by 21 and 27%, respectively. However, in subsequent tetani, both force and filament density recovered to preoscillation levels. These findings indicate that thick filaments in airway smooth muscle are labile, depolymerization of the myosin filaments can be induced by mechanical strain, and repolymerization of the thick filaments underlies force recovery after the oscillation. This thick-filament lability would greatly facilitate plastic changes of lattice length and explain why airway smooth muscle is able to function over a large length range.

Influence of calcium on myosin thick filament formation in intact airway smooth muscle

2002 ◽  
Vol 282 (2) ◽  
pp. C310-C316 ◽  
Author(s):  
Ana M. Herrera ◽  
Kuo-Hsing Kuo ◽  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Calcium Level ◽  
Muscle Activation ◽  
Isometric Force ◽  
Smooth Muscles ◽  
Thick Filament ◽  
Filament Formation ◽  
Cross Sectional ◽  
Thick Filaments

Myosin thick filaments have been shown to be structurally labile in intact smooth muscles. Although the mechanism of thick filament assembly/disassembly for purified myosins in solution has been well described, regulation of thick filament formation in intact muscle is still poorly understood. The present study investigates the effect of resting calcium level on thick filament maintenance in intact airway smooth muscle and on thick filament formation during activation. Cross-sectional density of the thick filaments measured electron microscopically showed that the density increased substantially (144%) when the muscle was activated. The abundance of filamentous myosins in relaxed muscle was calcium sensitive; in the absence of calcium (with EGTA), the filament density deceased by 35%. Length oscillation imposed on the muscle under zero-calcium conditions produced no further reduction in the density. Isometric force and filament density recovered fully after reincubation of the muscle in normal physiological saline. The results suggest that in airway smooth muscle, filamentous myosins exist in equilibrium with monomeric myosins; muscle activation favors filament formation, and the resting calcium level is crucial for preservation of the filaments in the relaxed state.

Time course of isotonic shortening and the underlying contraction mechanism in airway smooth muscle

2011 ◽  
Vol 111 (3) ◽  
pp. 642-656 ◽  
Author(s):  
Harley T. Syyong ◽  
Abdul Raqeeb ◽  
Peter D. Paré ◽  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Time Course ◽  
Muscle Activation ◽  
Striated Muscle ◽  
Myosin Filament ◽  
Disk Model ◽  
In Series ◽  
Force Velocity ◽  
Power Law Creep ◽  
Isotonic Shortening

Although the structure of the contractile unit in smooth muscle is poorly understood, some of the mechanical properties of the muscle suggest that a sliding-filament mechanism, similar to that in striated muscle, is also operative in smooth muscle. To test the applicability of this mechanism to smooth muscle function, we have constructed a mathematical model based on a hypothetical structure of the smooth muscle contractile unit: a side-polar myosin filament sandwiched by actin filaments, each attached to the equivalent of a Z disk. Model prediction of isotonic shortening as a function of time was compared with data from experiments using ovine tracheal smooth muscle. After equilibration and establishment of in situ length, the muscle was stimulated with ACh (100 μM) until force reached a plateau. The muscle was then allowed to shorten isotonically against various loads. From the experimental records, length-force and force-velocity relationships were obtained. Integration of the hyperbolic force-velocity relationship and the linear length-force relationship yielded an exponential function that approximated the time course of isotonic shortening generated by the modeled sliding-filament mechanism. However, to obtain an accurate fit, it was necessary to incorporate a viscoelastic element in series with the sliding-filament mechanism. The results suggest that a large portion of the shortening is due to filament sliding associated with muscle activation and that a small portion is due to continued deformation associated with an element that shows viscoelastic or power-law creep after a step change in force.

scholarly journals LOCALIZATION OF MYOSIN FILAMENTS IN SMOOTH MUSCLE

1968 ◽  
Vol 37 (1) ◽  
pp. 105-116 ◽  
Author(s):  
Robert E. Kelly ◽  
Robert V. Rice
Keyword(s):  
Smooth Muscle ◽  
Cross Section ◽  
Striated Muscle ◽  
Thick Filament ◽  
Longitudinal Axis ◽  
Thin Filaments ◽  
Chicken Gizzard ◽  
Thick Filaments ◽  
Myosin Filaments ◽  
Muscle Myosin

Thick myosin filaments, in addition to actin filaments, were found in sections of glycerinated chicken gizzard smooth muscle when fixed at a pH below 6.6. The thick filaments were often grouped into bundles and run in the longitudinal axis of the smooth muscle cell. Each thick filament was surrounded by a number of thin filaments, giving the filament arrangement a rosette appearance in cross-section. The exact ratio of thick filaments to thin filaments could not be determined since most arrays were not so regular as those commonly found in striated muscle. Some rosettes had seven or eight thin filaments surrounding a single thick filament. Homogenates of smooth muscle of chicken gizzard also showed both thick and thin filaments when the isolation was carried out at a pH below 6.6, but only thin filaments were found at pH 7.4. No Z or M lines were observed in chicken gizzard muscle containing both thick and thin filaments. The lack of these organizing structures may allow smooth muscle myosin to disaggregate readily at pH 7.4.

Models of contractile units and their assembly in smooth muscle

2005 ◽  
Vol 83 (10) ◽  
pp. 825-831 ◽  
Author(s):  
Farah Ali ◽  
Peter D Paré ◽  
Chun Y Seow
Keyword(s):  
Smooth Muscle ◽  
Striated Muscle ◽  
Dense Body ◽  
Unit Length ◽  
Muscle Length ◽  
Thick Filament ◽  
Contractile Apparatus ◽  
Thin Filaments ◽  
Dense Bodies ◽  
In Series

It is believed that the contractile filaments in smooth muscle are organized into arrays of contractile units (similar to the sarcomeric structure in striated muscle), and that such an organization is crucial for transforming the mechanical activities of actomyosin interaction into cell shortening and force generation. Details of the filament organization, however, are still poorly understood. Several models of contractile filament architecture are discussed here. To account for the linear relationship observed between the force generated by a smooth muscle and the muscle length at the plateau of an isotonic contraction, a model of contractile unit is proposed. The model consists of 2 dense bodies with actin (thin) filaments attached, and a myosin (thick) filament lying between the parallel thin filaments. In addition, the thick filament is assumed to span the whole contractile unit length, from dense body to dense body, so that when the contractile unit shortens, the amount of overlap between the thick and thin filaments (i.e., the distance between the dense bodies) decreases in exact proportion to the amount of shortening. Assembly of the contractile units into functional contractile apparatus is assumed to involve a group of cells that form a mechanical syncytium. The contractile apparatus is assumed malleable in that the number of contractile units in series and in parallel can be altered to accommodate strains on the muscle and to maintain the muscle's optimal mechanical function.Key words: contraction model, ultrastructure, length adaptation, plasticity.

Filament organization in vertebrate smooth muscle

1973 ◽  
Vol 265 (867) ◽  
pp. 223-229 ◽  
Keyword(s):  
Smooth Muscle ◽  
Thick Filament ◽  
Mesenteric Vein ◽  
Thick Filaments ◽  
Hypertonic Solutions ◽  
Cross Bridges

Thin (actin), thick (myosin) and interm ediate filaments are described in vertebrate smooth muscle. The thick filaments are present in relaxed, contracted, stretched and unstretched vertebrate smooth muscle and bear lateral projections suggestive of cross-bridges. The relatively regular thick filament lattice of the rabbit portal-anterior mesenteric vein can be aggregated by hypertonic solutions and excessive stretch. The interm ediate filaments are morphologically distinct and clearly not breakdown products of thick filaments.

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.

Myofibrillogenesis in the developing chicken heart: assembly of Z-disk, M-line and the thick filaments

1999 ◽  
Vol 112 (10) ◽  
pp. 1529-1539 ◽  
Author(s):  
E. Ehler ◽  
B.M. Rothen ◽  
S.P. Hammerle ◽  
M. Komiyama ◽  
J.C. Perriard
Keyword(s):  
Time Course ◽  
Dense Body ◽  
Thick Filament ◽  
Sarcomeric Proteins ◽  
Short Delay ◽  
Chicken Heart ◽  
Thick Filaments ◽  
Exact Position ◽  
Sarcomere Assembly

Myofibrillogenesis in situ was investigated by confocal microscopy of immunofluorescently labelled whole mount preparations of early embryonic chicken heart rudiments. The time-course of incorporation of several components into myofibrils was compared in triple-stained specimens, taken around the time when beating starts. All sarcomeric proteins investigated so far were already expressed before the first contractions and myofibril assembly happened within a few hours. No typical stress fibre-like structures or premyofibrils, structures observed in cultured cardiomyocytes, could be detected during myofibrillogenesis in the heart. Sarcomeric proteins like (α)-actinin, titin and actin were found in a defined localisation pattern even in cardiomyocytes that did not yet contain myofibrils, making up dense body-like structures. As soon as the heart started to beat, all myofibrillar proteins were already located at their exact position in the sarcomere. The maturation of the sarcomeres was characterised by a short delay in the establishment of the pattern for M-line epitopes of titin with respect to Z-disk epitopes and the incorporation of the M-line component myomesin, which preceded that of myosin binding protein-C. Thus dense body-like structures, made up of titin, (α)-actinin and actin filaments serve as the first organised complexes also during myofibrillogenesis in situ and titin functions as a ruler for sarcomere assembly as soon as its C termini have become localised. We suggest that assembly of thin and thick filament occurs independently during myofibrillogenesis in situ and that myomesin might be important for integrating thick filaments with the M-line end of titin.

Mechanical properties of tracheal smooth muscle: effects of temperature

1977 ◽  
Vol 233 (3) ◽  
pp. C92-C98 ◽  
Author(s):  
N. L. Stephens ◽  
R. Cardinal ◽  
B. Simmons
Keyword(s):  
Smooth Muscle ◽  
Tracheal Smooth Muscle ◽  
Effect Of Temperature ◽  
Contractile Element ◽  
Tension Development ◽  
In Series ◽  
Force Velocity ◽  
Effects Of Temperature ◽  
Active Processes ◽  
The Hill

The effect of temperature on the isometric tetanic myogram was studied in isolated canine tracheal smooth muscle (TSM). At 37 degrees C and 27 degrees C no significant change occurred in maximum tetanic tension (PO). At 17 degrees C a significant reduction was seen Values of Q10 for contraction time (tPO) were almost halved, whereas those for rate of tension development (dP/dt) were almost doubled. The effect of the same temperatures on the force-velocity (F-v) relationships was also studied. All three F-v curves were described by the Hill equation, (P + a) (v + b) = (PO + a)b. Vmax and b decreased with decreased temperature, with Q10's demonstrating they were dependent on active processes. Finally, the decreased dP/dt of the myogram at lower temperatures was felt to be the probable result of decreased contractile element velocity because no decrease in series elastic component stiffness was demonstrable, there being instead an increase in stiffness at lower temperatures.

Plasticity in smooth muscle, a hypothesis

1994 ◽  
Vol 72 (11) ◽  
pp. 1320-1324 ◽  
Author(s):  
Lincoln E. Ford ◽  
Chun Y. Seow ◽  
Victor R. Pratusevich
Keyword(s):  
Smooth Muscle ◽  
Preliminary Finding ◽  
Muscle Length ◽  
Shortening Velocity ◽  
Thin Filaments ◽  
Thick Filaments ◽  
Initial Hypothesis ◽  
In Series ◽  
Cross Bridges ◽  
Muscle Myosin

The controversial finding that the thick filaments of smooth muscle can be evanescent leads to the hypothesis that the large functional range of this muscle is accommodated by plastic rearrangements that place more thick filaments in series at longer lengths. Our preliminary finding that the shortening velocity and compliance of dog tracheal muscle were strongly dependent on adapted muscle length, while force was much less length dependent, supports this hypothesis (V.R. Pratusevich, C.Y. Seow, and L.E. Ford. Biophys. J. 66: A139, 1994). The hypothesis leads to two further corollaries. The first is that the lengthening of the thick filaments that must accompany their reformation will cause a series to parallel transition: fewer long filaments span the muscle length, but the longer filaments have more cross bridges acting in parallel. The second is that there is more than one activating mechanism in smooth muscle. It is known that myosin light chain phosphorylation activates the actomyosin ATPase, but this same phosphorylation also causes a structural change that facilitates filament formation. The consideration that the unaggregated, phosphorylated myosin must be prevented from competing with myosin in thick filaments and hydrolyzing ATP suggests that there must be a second mechanism that must allow the thin filaments to interact selectively with filamentous myosin. This need for a second activating mechanism may explain the presence of tropomyosin, calponin, and caldesmon on thin filaments. Although the two corollaries follow from the initial hypothesis, it should be emphasized that the three are not mutually dependent, and that the proof or disproof of any one of them would not prove or disprove the others.Key words: smooth muscle, myosin, thick filaments, contraction.

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