Contraction history modulates isotonic shortening velocity in smooth muscle

1993 ◽  
Vol 265 (2) ◽  
pp. C467-C476 ◽  
Author(s):  
S. J. Gunst ◽  
M. F. Wu ◽  
D. D. Smith
Keyword(s):  
Smooth Muscle ◽  
Muscle Length ◽  
Electrical Field Stimulation ◽  
Contractile Element ◽  
Shortening Velocity ◽  
Linear Rate ◽  
Velocity Relationship ◽  
Force Velocity ◽  
Contractile Activation ◽  
Isotonic Shortening

The effect of contraction history on the isotonic shortening velocity of canine tracheal smooth muscle was investigated. Muscles were contracted isometrically for 20 s at initial lengths of L(o) (length of maximal active force), 85% L(o), or 70% L(o) using electrical field stimulation. Muscles were then allowed to shorten isotonically under different afterloads either with or without first being subjected to a step decrease in length to 70% L(o). Instantaneous velocities were plotted against instantaneous muscle length during isotonic shortening. Regardless of protocol, the velocity at any muscle length during shortening was lower when the muscle was initially activated at a longer length. The isotonic shortening velocity decreased progressively during shortening at a nearly linear rate with respect to instantaneous muscle length under all conditions. Results suggest that a longer muscle length at the time of activation leads to the development of higher loads on the contractile element during subsequent shortening, resulting in a slower shortening velocity. This plasticity of the force-velocity relationship may result from cytostructural reorganization of the smooth muscle cells in response to contractile activation at different muscle lengths.

Myosin phosphorylation and contraction of feline esophageal smooth muscle

1985 ◽  
Vol 249 (1) ◽  
pp. C9-C14 ◽  
Author(s):  
N. W. Weisbrodt ◽  
R. A. Murphy
Keyword(s):  
Smooth Muscle ◽  
Mechanical Activation ◽  
Smooth Muscles ◽  
Circular Muscle ◽  
Electrical Field Stimulation ◽  
Muscle Layer ◽  
Field Stimulation ◽  
Shortening Velocity ◽  
Myosin Phosphorylation ◽  
Isotonic Shortening

We tested the hypothesis that phosphorylation of the 20,000-Da light chain of myosin (LC 20) is related to mechanical activation of esophageal smooth muscle. Circular muscle layer strips of cat esophagus were taken from the lower esophageal sphincter (LES) and the distal esophageal body (EB). The LES strips developed tone spontaneously, and the EB strips were tonically contracted with carbachol. Both tissues relaxed in response to electrical-field stimulation. Phosphorylation of the LC 20 was determined in tissues quick-frozen during relaxation and during stress redevelopment after cessation of field stimulation. Stress and phosphorylation levels were low after 30 s of field stimulation, and a rapid contraction followed field stimulation. Phosphorylation in the LES increased from 0.043 +/- 0.029 to 0.328 +/- 0.043 mol Pi/mol LC 20 within 10 s after stimulation of the inhibitory nerves was terminated, while stress was still rising rapidly. Phosphorylation in the LES then declined to a steady-state value of 0.162 +/- 0.034 mol Pi/mol LC 20 after 10 min. Isotonic shortening velocities at a constant afterload following a quick release showed changes with time that were proportional to the level of phosphorylation. This was also true for values of maximal shortening velocity estimated for zero external load and for the rate of stress redevelopment after a step shortening. Comparable measurements were made in the carbachol-contracted EB. These results indicate that visceral smooth muscles, which normally function tonically (LES) or phasically (EB), exhibit an initial rapid mechanical activation associated with myosin phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Force-velocity relationship of expiratory muscles in normal subjects

1982 ◽  
Vol 52 (4) ◽  
pp. 930-938 ◽  
Author(s):  
Y. Kikuchi ◽  
H. Sasaki ◽  
K. Sekizawa ◽  
K. Aihara ◽  
T. Takishima
Keyword(s):  
Respiratory Muscles ◽  
Normal Subjects ◽  
Contractile Element ◽  
Shortening Velocity ◽  
Mean Values ◽  
Significant Difference ◽  
Velocity Relationship ◽  
Force Velocity ◽  
Expiratory Muscles ◽  
Relationship Of

We examined the force-velocity relationship of the respiratory muscles in normal subjects under nearly isotonic conditions, taking into consideration the pleural pressure (Ppl) changes during maximum forced expirations (MFE). We used an electromagnetic valve (EMV) to select the Ppl value at the onset of mouth flow; and both a pressure reservoir and a variable resistance to control the Ppl changes after the opening of the EMV during MFE. To simulate isotonic conditions and to obtain the shortening velocity of the contractile element (CE), we mathematically corrected the velocity of the series elastic component (SEC), using a modified version of Hill's equation. Although the maximum tension at total lung capacity (TLC) [1,156 +/- 215 (SD) g/cm] was larger than that at functional residual capacity (FRC) (782 +/- 97 g/cm) there was no significant difference in the maximum shortening velocity, 3.4 +/- 1.0 and 3.2 +/- 0.8 circumference/s at TLC and FRC, respectively. The mean values of k (slope) for the SEC at TLC and FRC were 19 +/- 4 and 18 +/- 5 circumference-1, respectively, and they were not significantly different. We concluded that the force-velocity relationship of the expiratory muscles exhibited the same mechanical properties as that of the other skeletal muscles.

Effect of airway inflammation on smooth muscle shortening and contractility in guinea pig trachealis

1993 ◽  
Vol 265 (6) ◽  
pp. L549-L554 ◽  
Author(s):  
R. W. Mitchell ◽  
I. M. Ndukwu ◽  
K. Arbetter ◽  
J. Solway ◽  
A. R. Leff
Keyword(s):  
Smooth Muscle ◽  
Guinea Pig ◽  
Neurogenic Inflammation ◽  
Isometric Force ◽  
Electrical Field Stimulation ◽  
Shortening Velocity ◽  
Lever System ◽  
Force Velocity

We studied the effect of either 1) immunogenic inflammation caused by aerosolized ovalbumin or 2) neurogenic inflammation caused by aerosolized capsaicin in vivo on guinea pig tracheal smooth muscle (TSM) contractility in vitro. Force-velocity relationships were determined for nine epithelium-intact TSM strips from ovalbumin-sensitized (OAS) vs. seven sham-sensitized controls and TSM strips for seven animals treated with capsaicin aerosol (Cap-Aer) vs. eight sham controls. Muscle strips were tethered to an electromagnetic lever system, which allowed isotonic shortening when load clamps [from 0 to maximal isometric force (Po)] were applied at specific times after onset of contraction. Contractions were elicited by supramaximal electrical field stimulation (60 Hz, 10-s duration, 18 V). Optimal length for each muscle was determined during equilibration. Maximal shortening velocity (Vmax) was increased in TSM from OAS (1.72 +/- 0.46 mm/s) compared with sham-sensitized animals (0.90 +/- 0.15 mm/s, P < 0.05); Vmax for TSM from Cap-Aer (0.88 +/- 0.11 mm/s) was not different from control TSM (1.13 +/- 0.08 mm/s, P = NS). Similarly, maximal shortening (delta max) was augmented in TSM from OAS (1.01 +/- 0.15 mm) compared with sham-sensitized animals (0.72 +/- 0.14 mm, P < 0.05); delta max for TSM from Cap-Aer animals (0.65 +/- 0.11 mm) was not different from saline aerosol controls (0.71 +/- 0.15 mm, P = NS). We demonstrate Vmax and delta max are augmented in TSM after ovalbumin sensitization; in contrast, neurogenic inflammation caused by capsaicin has no effect on isolated TSM contractility in vitro. These data suggest that airway hyperresponsiveness in vivo that occurs in association with immunogenic or neurogenic inflammation may result from different effects of these types of inflammation on airway smooth muscle.

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.

Maximum shortening velocity of smooth muscle: zero load-clamp vs. afterloaded method

1983 ◽  
Vol 55 (5) ◽  
pp. 1630-1633 ◽  
Author(s):  
R. W. Mitchell ◽  
N. L. Stephens
Keyword(s):  
Smooth Muscle ◽  
Direct Measurement ◽  
Hill Equation ◽  
Shortening Velocity ◽  
Optimal Length ◽  
Lever System ◽  
Technical Advances ◽  
Force Velocity ◽  
The Hill ◽  
Isotonic Shortening

Previous reports from this laboratory of force-velocity relationships of canine tracheal smooth muscle (TSM) have presented maximum shortening velocities (Vmax) mathematically derived from the linearized transformation of the Hill equation (A. V. Hill, Proc. Roy. Soc. London, Ser. B., 126:136-195, 1938). Recent technical advances enable us to measure Vmax directly using an electromagnetic lever system that can instantaneously clamp to a zero load, thus we compared values of Vmax derived mathematically and those directly measured on the same TSM strips. Derived Vmax values from afterloaded isotonic shortening curves for loads greater than preload were 0.328 +/- 0.021 optimal length (lO)/s and were not significantly different from zero load-clamp measurements of 0.301 +/- 0.022 lO/s from the same (n = 15) muscles. These data indicate that Vmax values mathematically derived for TSM from conventional isotonic afterloaded force-velocity curves are valid estimates of zero load velocity, because they were not significantly different from values obtained by direct measurement using the zero load-clamp technique.

scholarly journals Dissociation between hysteresivity and tension in constricted tracheal and parenchymal strips

1998 ◽  
Vol 85 (1) ◽  
pp. 91-97 ◽  
Author(s):  
Francesco G. Salerno ◽  
Mara S. Ludwig
Keyword(s):  
Smooth Muscle ◽  
Electrical Field Stimulation ◽  
Lung Parenchyma ◽  
Hysteretic Behavior ◽  
Contractile Element ◽  
Organ Bath ◽  
Field Stimulation ◽  
Shortening Velocity ◽  
Electrical Field ◽  
Contractile State

The object of this study was to investigate how changes in the contractile state of smooth muscle would modify oscillatory mechanics of tracheal muscle and lung parenchyma during agonist challenge. Guinea pig tracheal and parenchymal lung strips were suspended in an organ bath. Measurements of length ( L) and tension (T) were recorded during sinusoidal oscillations under baseline conditions and after challenge with 1 mM ACh. Measurements were also obtained in strips pretreated with the calmodulin inhibitor calmidazolium (Cmz) or staurosporine (Stauro), a protein kinase C inhibitor. Elastance (E) and resistance (R) were calculated by fitting changes in T, L, and Δ L/Δ tto the equation of motion. Hysteresivity (η) was obtained from the following equation: η = (R/E)2π f, where f is frequency. Finally, maximal unloaded shortening velocity during electrical field stimulation was measured in Cmz-pretreated and control tracheal strips. In tracheal strips, pretreatment with Cmz caused a significant decrease in the η response to ACh challenge and in maximal unloaded shortening velocity measured during electrical field stimulation; Stauro decreased the T, E, and R response to ACh. In parenchymal strips, Cmz decreased the η response, whereas Stauro had no effect. These results suggest that modifications in the contractile state of the smooth muscle are reflected in changes in the hysteretic behavior and that T and η may be controlled independently. Second, inasmuch as changes in η were similar in parenchymal and tracheal strips, the contractile element is implicated as the structure responsible for constriction-induced changes in the mechanical behavior of the lung periphery.

Transient length-related mechanical states in smooth muscle

1994 ◽  
Vol 72 (11) ◽  
pp. 1325-1333 ◽  
Author(s):  
Richard A. Meiss
Keyword(s):  
Mechanical Properties ◽  
Mathematical Model ◽  
Smooth Muscle ◽  
Internal Resistance ◽  
Steady Increase ◽  
Kinetic Properties ◽  
Shortening Velocity ◽  
Force Velocity ◽  
Isotonic Contractions ◽  
Isotonic Shortening

The isotonic shortening of electrically stimulated ovarian ligament smooth muscle strips from rabbits was studied by briefly applying sudden increases in afterload (force steps, 0.6 to 3.0 s long) just sufficient to halt the shortening. Upon removal of the extra afterload, the isotonic shortening velocity significantly increased compared with prestep velocities measured at the same muscle lengths. The degree of potentiation depended upon the duration of the force step. Muscles yielded initially when the step was applied, and their stiffness decreased. During the zero-velocity portion of the force step there was a steady increase in stiffness back to levels appropriate to that force. Complete force–velocity curves were made following short (0.6 s) and long (3.0 s) force steps. The values for Vmax (and all intermediate velocities) were significantly greater following a long force step. In a final experimental series, muscles were held isometric immediately after removal of the force step. Force rose monotonically, with a more rapid redevelopment following a long force step. A mathematical model is presented, according to which the effect of the duration of the force step on the poststep mechanical properties may be due to either the alteration of an internal resistance to shortening or a change in the kinetic properties of the cross-bridge array. A hypothesis is proposed relating the steady decline in isotonic shortening velocity to a partial local depletion of energy-yielding substrates.Key words: smooth muscle, isotonic contractions, mechanics, models.

Relative shortening velocity in locomotor muscles: turkey ankle extensors operate at low V/Vmax

2008 ◽  
Vol 294 (1) ◽  
pp. R200-R210 ◽  
Author(s):  
Annette M. Gabaldón ◽  
Frank E. Nelson ◽  
Thomas J. Roberts
Keyword(s):  
Isometric Force ◽  
Muscle Length ◽  
Shortening Velocity ◽  
Velocity Relationship ◽  
Locomotor Muscles ◽  
Force Velocity ◽  
Wild Turkeys ◽  
Strain Gauge Measurements ◽  
All Speeds ◽  
Level Running

The force-velocity properties of skeletal muscle have an important influence on locomotor performance. All skeletal muscles produce less force the faster they shorten and typically develop maximal power at velocities of ∼30% of maximum shortening velocity (Vmax). We used direct measurements of muscle mechanical function in two ankle extensor muscles of wild turkeys to test the hypothesis that during level running muscles operate at velocities that favor force rather than power. Sonomicrometer measurements of muscle length, tendon strain-gauge measurements of muscle force, and bipolar electromyographs were taken as animals ran over a range of speeds and inclines. These measurements were integrated with previously measured values of muscle Vmax for these muscles to calculate relative shortening velocity (V/Vmax). At all speeds for level running the V/Vmax values of the lateral gastrocnemius and the peroneus longus were low (<0.05), corresponding to the region of the force-velocity relationship where the muscles were capable of producing 90% of peak isometric force but only 35% of peak isotonic power. V/Vmax increased in response to the demand for mechanical power with increases in running incline and decreased to negative values to absorb energy during downhill running. Measurements of integrated electromyograph activity indicated that the volume of muscle required to produce a given force increased from level to uphill running. This observation is consistent with the idea that V/Vmax is an important determinant of locomotor cost because it affects the volume of muscle that must be recruited to support body weight.

Selected Contribution: Effect of chronic passive length change on airway smooth muscle length-tension relationship

2001 ◽  
Vol 90 (2) ◽  
pp. 734-740 ◽  
Author(s):  
Lu Wang ◽  
Peter D. Paré ◽  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Force Production ◽  
Muscle Length ◽  
Electrical Field Stimulation ◽  
Length Change ◽  
Electrical Field ◽  
Optimal Length ◽  
Active Length ◽  
Reference Length ◽  
Relationship Of

The ability of rabbit trachealis to undergo plastic adaptation to chronic shortening or lengthening was assessed by setting the muscle preparations at three lengths for 24 h in relaxed state: a reference length in which applied force was ∼1–2% of maximal active force (Po) and lengths considerably shorter and longer than the reference. Passive and active length-tension ( L-T) curves for the preparations were then obtained by electrical field stimulation at progressively increasing muscle length. Classically shaped L-T curves were obtained with a distinct optimal length ( L o) at which Podeveloped; however, both the active and passive L-T curves were shifted, whereas Po remained unchanged. L o was 72% and 148% that of the reference preparations for the passively shortened and lengthened muscles, respectively. The results suggest that chronic narrowing of the airways could induce a shift in the L-T relationship of smooth muscle, resulting in a maintained potential for maximal force production.

scholarly journals Power fatigue of the rat diaphragm muscle

2000 ◽  
Vol 89 (6) ◽  
pp. 2215-2219 ◽  
Author(s):  
Bill T. Ameredes ◽  
Wen-Zhi Zhan ◽  
Y. S. Prakash ◽  
Rene Vandenboom ◽  
Gary C. Sieck
Keyword(s):  
Diaphragm Muscle ◽  
Fiber Types ◽  
Rat Diaphragm ◽  
Shortening Velocity ◽  
Reduction In Force ◽  
Novel Technique ◽  
Velocity Relationship ◽  
Stimulus Train ◽  
Force Velocity

We hypothesized that decrements in maximum power output (W˙max) of the rat diaphragm (Dia) muscle with repetitive activation are due to a disproportionate reduction in force (force fatigue) compared with a slowing of shortening velocity (velocity fatigue). Segments of midcostal Dia muscle were mounted in vitro (26°C) and stimulated directly at 75 Hz in 400-ms-duration trains repeated each second (duty cycle = 0.4) for 120 s. A novel technique was used to monitor instantaneous reductions in maximum specific force (Po) andW˙max during fatigue. During each stimulus train, activation was isometric for the initial 360 ms during which Po was measured; the muscle was then allowed to shorten at a constant velocity (30% V max) for the final 40 ms, and W˙max was determined. Compared with initial values, after 120 s of repetitive activation, Po andW˙max decreased by 75 and 73%, respectively. Maximum shortening velocity was measured in two ways: by extrapolation of the force-velocity relationship ( V max) and using the slack test [maximum unloaded shortening velocity ( V o)]. After 120 s of repetitive activation, V max slowed by 44%, whereas V o slowed by 22%. Thus the decrease inW˙max with repetitive activation was dominated by force fatigue, with velocity fatigue playing a secondary role. On the basis of a greater slowing of V max vs. V o, we also conclude that force and power fatigue cannot be attributed simply to the total inactivation of the most fatigable fiber types.

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