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.

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.

Cross-bridge dephosphorylation and relaxation of vascular smooth muscle

1989 ◽  
Vol 256 (2) ◽  
pp. C282-C287 ◽  
Author(s):  
C. M. Hai ◽  
R. A. Murphy
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Time Course ◽  
Electrical Field Stimulation ◽  
Shortening Velocity ◽  
Electrical Field ◽  
Cross Bridge ◽  
Time Course Data ◽  
Necessary And Sufficient ◽  
Isotonic Shortening

We tested the hypothesis that relaxation in vascular smooth muscle is the result of inactivation of myosin light chain kinase and cross-bridge dephosphorylation. Fast neurally mediated contractions of swine carotid medial strips were induced by electrical field stimulation. Termination of the stimulus resulted in relaxation with a half time of 2 min. Nifedipine (0.1 microM) increased the relaxation rate without significant effects on the contractile response. Cross-bridge dephosphorylation was much faster than stress decay with basal levels reached within 1 min when 73% of the developed stress remained. The time-course data of dephosphorylation and stress were analyzed with a model that predicted the dependences of stress and isotonic shortening velocity on cross-bridge phosphorylation during contraction. Rate constants resolved from contraction data also fitted the relaxation data when the model's prediction was corrected for estimated errors in the phosphorylation measurements. Because Ca2+-dependent cross-bridge phosphorylation was the only postulated regulatory mechanism in the model, these results are consistent with the hypothesis that cross-bridge dephosphorylation is necessary and sufficient to explain relaxation in the swine carotid media.

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.

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.

Dissecting muscle power output

1999 ◽  
Vol 202 (23) ◽  
pp. 3369-3375 ◽  
Author(s):  
R.K. Josephson
Keyword(s):  
Time Course ◽  
Muscle Activation ◽  
Muscle Force ◽  
Muscle Power ◽  
Muscle Length ◽  
Velocity Relationship ◽  
Shortening Deactivation ◽  
Force Velocity ◽  
Work Done ◽  
Kinetics Of

The primary determinants of muscle force throughout a shortening-lengthening cycle, and therefore of the net work done during the cycle, are (1) the shortening or lengthening velocity of the muscle and the force-velocity relationship for the muscle, (2) muscle length and the length-tension relationship for the muscle, and (3) the pattern of stimulation and the time course of muscle activation following stimulation. In addition to these primary factors, there are what are termed secondary determinants of force and work output, which arise from interactions between the primary determinants. The secondary determinants are length-dependent changes in the kinetics of muscle activation, and shortening deactivation, the extent of which depends on the work that has been done during the preceding shortening. The primary and secondary determinants of muscle force and work are illustrated with examples drawn from studies of crustacean muscles.

Contractile properties of bronchial smooth muscle with and without cartilage

1990 ◽  
Vol 69 (1) ◽  
pp. 120-126 ◽  
Author(s):  
H. Jiang ◽  
N. L. Stephens
Keyword(s):  
Smooth Muscle ◽  
Bronchial Tree ◽  
Isometric Tension ◽  
Bronchial Smooth Muscle ◽  
Optimal Length ◽  
Resting Tension ◽  
Force Velocity ◽  
Later Phase ◽  
Isotonic Shortening

The majority of in vitro studies on airway smooth muscle have used the trachealis (TSM) as a convenient substitute for muscle from airways that constitute the flow-limiting segment. The latter are technically difficult to work with. However, because the site of maximum resistance to airflow is at the third to seventh generations of the bronchial tree, the trachealis preparation is of limited value. Length-tension and force-velocity properties were therefore studied at optimal length (lo) of canine bronchial smooth muscle (BSM) from which cartilage had been carefully removed. Normalized maximum isometric tension or stress (Po x 10(4) N/m2) for BSM was 7.1 +/- 0.19 (SE), which was similar to that of BSM with cartilage (BSM+C, 6.8 +/- 0.21) but lower than for TSM (18.2 +/- 0.81). At length greater than lo, the BSM+C was stiffer than the BSM. The values of maximum shortening capacity (delta Lmax), obtained directly from isotonic shortening at a load equal to the resting tension at lo, were 0.76 lo +/- 0.03, 0.41 lo +/- 0.02, and 0.24 +/- 0.02 lo for TSM, BSM, and BSM+C, respectively. The BSM and BSM+C delta Lmaxs were different (P less than 0.05). Maximal shortening velocities (Vo) for BSM, elicited at 2, 4, and 8 s by quick release in the course of an isometric contraction were significantly higher than for the BSM+C. Vos showed gradual decreases in all three groups in the later phase of contraction, suggesting the operation of latch bridges.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

scholarly journals The Huxley crossbridge model as the basic mechanism for airway smooth muscle contraction

2019 ◽  
Vol 317 (2) ◽  
pp. L235-L246 ◽  
Author(s):  
Ling Luo ◽  
Lu Wang ◽  
Peter D. Paré ◽  
Chun Y. Seow ◽  
Pasquale Chitano
Keyword(s):  
Smooth Muscle ◽  
Muscle Contraction ◽  
Airway Smooth Muscle ◽  
Time Course ◽  
Striated Muscle ◽  
Isometric Force ◽  
Smooth Muscle Contraction ◽  
Time Dependent ◽  
Shortening Velocity ◽  
Mlc20 Phosphorylation

The cyclic interaction between myosin crossbridges and actin filaments underlies smooth muscle contraction. Phosphorylation of the 20-kDa myosin light chain (MLC20) is a crucial step in activating the crossbridge cycle. Our current understanding of smooth muscle contraction is based on observed correlations among MLC20 phosphorylation, maximal shortening velocity ( Vmax), and isometric force over the time course of contraction. However, during contraction there are changes in the extent of phosphorylation of many additional proteins as well as changes in activation of enzymes associated with the signaling pathways. As a consequence, the mechanical manifestation of muscle contraction is likely to change with time. To simplify the study of these relationships, we measured the mechanical properties of airway smooth muscle at different levels of MLC20 phosphorylation at a fixed time during contraction. A simple correlation emerged when time-dependent variables were fixed. MLC20 phosphorylation was found to be directly and linearly correlated with the active stress, stiffness, and power of the muscle; the observed weak dependence of Vmax on MLC20 phosphorylation could be explained by the presence of an internal load in the muscle preparation. These results can be entirely explained by the Huxley crossbridge model. We conclude that when the influence of time-dependent events during contraction is held constant, the basic crossbridge mechanism in smooth muscle is the same as that in striated muscle.

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