Effects of microtubule disruption on force, velocity, stiffness and [Ca2+]i in porcine coronary arteries

2000 ◽  
Vol 279 (5) ◽  
pp. H2493-H2501 ◽  
Author(s):  
Richard J. Paul ◽  
Peggy Sue Bowman ◽  
Michael S. Kolodney
Keyword(s):  
Smooth Muscle ◽  
Coronary Arteries ◽  
Isometric Force ◽  
Shortening Velocity ◽  
Cultured Fibroblasts ◽  
Microtubule Disruption ◽  
Highly Sensitive ◽  
Artery Stiffness ◽  
Force Velocity ◽  
Microtubule Stabilizer

Force generated by smooth muscle cells is believed to result from the interaction of actin and myosin filaments and is regulated through phosphorylation of the myosin regulatory light chain (LC20). The role of other cytoskeleton filaments, such as microtubules and intermediate filaments, in determining the mechanical output of smooth muscle is unclear. In cultured fibroblasts, microtubule disruption results in large increases in force similar to contractions associated with LC20 phosphorylation (15). One hypothesis, the “tensegrity” or “push-pull” model, attributes this increase in force to the disruption of microtubules functioning as rigid struts to resist force generated by actin-myosin interaction (9). In porcine coronary arteries, the disruption of microtubules by nocodazole (11 μM) also elicited moderate but significant increases in isometric force (10–40% of a KCl contracture), which could be blocked or reversed by taxol (a microtubule stabilizer). We tested whether this nocodazole-induced force was accompanied by changes in coronary artery stiffness or unloaded shortening velocity, parameters likely to be highly sensitive to microtubule resistance elements. Few changes were seen, ruling out push-pull mechanisms for the increase in force by nocodazole. In contrast, the intracellular calcium concentration, measured by fura 2 in the intact artery, was increased by nocodazole in parallel with force, and this was inhibited and/or reversed by taxol. Our results indicate that microtubules do not significantly contribute to vascular smooth muscle mechanical characteristics but, importantly, may play a role in modulation of Ca2+ signal transduction.

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.

Force-velocity and force-power properties of single muscle fibers from elite master runners and sedentary men

1996 ◽  
Vol 271 (2) ◽  
pp. C676-C683 ◽  
Author(s):  
J. J. Widrick ◽  
S. W. Trappe ◽  
D. L. Costill ◽  
R. H. Fitts
Keyword(s):  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Power Output ◽  
Peak Power ◽  
Isometric Force ◽  
Peak Force ◽  
Peak Power Output ◽  
Type I ◽  
Shortening Velocity ◽  
Force Velocity

Gastrocnemius muscle fiber bundles were obtained by needle biopsy from five middle-aged sedentary men (SED group) and six age-matched endurance-trained master runners (RUN group). A single chemically permeabilized fiber segment was mounted between a force transducer and a position motor, subjected to a series of isotonic contractions at maximal Ca2+ activation (15 degrees C), and subsequently run on a 5% polyacrylamide gel to determine myosin heavy chain composition. The Hill equation was fit to the data obtained for each individual fiber (r2 > or = 0.98). For the SED group, fiber force-velocity parameters varied (P < 0.05) with fiber myosin heavy chain expression as follows: peak force, no differences: peak tension (force/fiber cross-sectional area), type IIx > type IIa > type I; maximal shortening velocity (Vmax, defined as y-intercept of force-velocity relationship), type IIx = type IIa > type I; a/Pzero (where a is a constant with dimensions of force and Pzero is peak isometric force), type IIx > type IIa > type I. Consequently, type IIx fibers produced twice as much peak power as type IIa fibers, whereas type IIa fibers produced about five times more peak power than type I fibers. RUN type I and IIa fibers were smaller in diameter and produced less peak force than SED type I and IIa fibers. The absolute peak power output of RUN type I and IIa fibers was 13 and 27% less, respectively, than peak power of similarly typed SED fibers. However, type I and IIa Vmax and a/Pzero were not different between the SED and RUN groups, and RUN type I and IIa power deficits disappeared after power was normalized for differences in fiber diameter. Thus the reduced absolute peak power output of the type I and IIa fibers from the master runners was a result of the smaller diameter of these fibers and a corresponding reduction in their peak isometric force production. This impairment in absolute peak power production at the single fiber level may be in part responsible for the reduced in vivo power output previously observed for endurance-trained athletes.

Aminophylline increases submaximum power but not intrinsic velocity of shortening of frog muscle

1992 ◽  
Vol 73 (1) ◽  
pp. 71-74 ◽  
Author(s):  
B. M. Block ◽  
S. R. Barry ◽  
J. A. Faulkner
Keyword(s):  
Skeletal Muscles ◽  
Isometric Force ◽  
Frog Muscle ◽  
Measured Parameter ◽  
Shortening Velocity ◽  
Force Development ◽  
Velocity Of Shortening ◽  
Force Velocity ◽  
Maximum Isometric Force ◽  
Frequency Of Stimulation

We hypothesized that methylxanthines, such as aminophylline, increase the power developed by submaximally activated frog skeletal muscles by increasing the force developed at any given velocity of shortening. Frog semitendinosus muscles were excised and tested at 20 degrees C in oxygenated control and aminophylline Ringer solutions. Force-velocity relationships were determined and power was calculated from muscles stimulated at frequencies of 80 and 300 Hz. The 300-Hz frequency of stimulation produced a maximum rate of force development. In 50 and 500 microM aminophylline, twitch force increased by 25 +/- 12 and 75 +/- 13%, respectively. Aminophylline did not affect maximum isometric force generation or the shortening velocity at any relative load. At 80-Hz stimulation and in the presence of 500 microM aminophylline, power increased by an average of 11% at 10 of 14 relative loads. At maximum frequencies of stimulation, aminophylline had no effect on any measured parameter. We conclude that aminophylline increases the power developed by submaximally activated frog muscles through an increase in the force generated particularly at the lower velocities of shortening.

Vanadate oxidation activates contraction in skinned smooth muscle without myosin light chain phosphorylation

1997 ◽  
Vol 272 (1) ◽  
pp. C278-C288 ◽  
Author(s):  
M. J. Lalli ◽  
K. Obara ◽  
R. J. Paul
Keyword(s):  
Smooth Muscle ◽  
Light Chain ◽  
Muscle Activation ◽  
Isometric Force ◽  
Total Force ◽  
Shortening Velocity ◽  
Irreversible Damage ◽  
Initial Control ◽  
High Concentrations ◽  
Cross Bridges

Phosphorylation of the myosin regulatory light chain (LC20-P1) is the major route of smooth muscle activation. However, after prior exposure to vanadate, permeabilized guinea pig taenia coli smooth muscle contracts in the absence of LC20-P1. We characterized the vanadate-induced contraction and investigated the mechanism of this novel activation pathway. Addition of vanadate to a control contracture (6.6 microM Ca2+) inhibits force (effective dose for 50% response was approximately 100 microM). In contrast, preincubation with high concentrations of vanadate (threshold at 1-2 mM) elicited a contraction on subsequent transfer of the fiber to a vanadate-free, Ca(2+)-free solution. Maximum isometric force of approximately 60% of control was obtained in fibers preincubated in 4 mM vanadate for 10 min. Addition of Ca2+ to a vanadate-induced contracture increased force, but the total force never exceeded the initial control. After maximal thiophosphorylation of LC20 with adenosine 5'-O-(3-thiotriphosphate), treatment with vanadate did not increase force. Unloaded shortening velocity (Vmax) was similar in Ca2+ and vanadate contractures and was additive. After thiophosphorylation, preincubation in vanadate had no effect on Vmax, suggesting that vanadate affected the number of activated bridges and not cycle rate. Vanadate mechanisms likely involve oxidation, since preincubation with 4 mM vanadate and 25 mM dithiothreitol (DTT) did not produce force. DTT could reverse a vanadate-induced contracture in 30-60 min. Subsequently, fibers demonstrated control contraction/relaxation cycles. Thus vanadate treatment did not cause irreversible damage, such as the extraction of proteins. Potential oxidation sites are proteins at 17 kDa and between 30 and 40 kDa, which were not alkylated by N-ethylmaleimide if they were treated in the presence of vanadate or in the rigor state. Vanadate-induced contractures are likely mediated by a reversible oxidation that activates cross bridges similarly to that of LC20-Pi and may play an important role in oxidant injury.

scholarly journals The maximum shortening velocity of muscle should be scaled with activation

1999 ◽  
Vol 86 (3) ◽  
pp. 1025-1031 ◽  
Author(s):  
John W. Chow ◽  
Warren G. Darling
Keyword(s):  
Isometric Force ◽  
Musculoskeletal Modeling ◽  
Type Model ◽  
Shortening Velocity ◽  
Activation Level ◽  
Maximum Activation ◽  
Force Velocity ◽  
Maximum Isometric Force ◽  
Release Method ◽  
Wrist Flexors

The purpose of this study was to determine whether the maximum shortening velocity ( V max) in Hill’s mechanical model (A. V. Hill. Proc. R. Soc. London Ser. B. 126: 136–195, 1938) should be scaled with activation, measured as a fraction of the maximum isometric force (Fmax). By using the quick-release method, force-velocity (F-V) relationships of the wrist flexors were gathered at five different activation levels (20–100% of maximum at intervals of 20%) from four subjects. The F-V data at different activation levels can be fitted remarkably well with Hill’s characteristic equation. In general, the shortening velocity decreases with activation. With the assumption of nonlinear relationships between Hill constants and activation level, a scaled V max model was developed. When the F-V curves for submaximal activation were forced to converge at the V max obtained with maximum activation (constant V max model), there were drastic changes in the shape of the curves. The differences in V max values generated by the scaled and constant V max models were statistically significant. These results suggest that, when a Hill-type model is used in musculoskeletal modeling, the V max should be scaled with activation.

scholarly journals Slowing of velocity during isotonic shortening in single isolated smooth muscle cells. Evidence for an internal load.

1990 ◽  
Vol 96 (3) ◽  
pp. 581-601 ◽  
Author(s):  
D E Harris ◽  
D M Warshaw
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Isometric Force ◽  
Muscle Cells ◽  
Force Transducer ◽  
Cell Stiffness ◽  
Shortening Velocity ◽  
Internal Load ◽  
Isolated Smooth Muscle Cells ◽  
Isotonic Shortening

In single smooth muscle cells, shortening velocity slows continuously during the course of an isotonic (fixed force) contraction (Warshaw, D.M. 1987. J. Gen. Physiol. 89:771-789). To distinguish among several possible explanations for this slowing, single smooth muscle cells were isolated from the gastric muscularis of the toad (Bufo marinus) and attached to an ultrasensitive force transducer and a length displacement device. Cells were stimulated electrically and produced maximum stress of 144 mN/mm2. Cell force was then reduced to and maintained at preset fractions of maximum, and cell shortening was allowed to occur. Cell stiffness, a measure of relative numbers of attached crossbridges, was measured during isotonic shortening by imposing 50-Hz sinusoidal force oscillations. Continuous slowing of shortening velocity was observed during isotonic shortening at all force levels. This slowing was not related to the time after the onset of stimulation or due to reduced isometric force generating capacity. Stiffness did not change significantly over the course of an isotonic shortening response, suggesting that the observed slowing was not the result of reduced numbers of cycling crossbridges. Furthermore, isotonic shortening velocity was better described as a function of the extent of shortening than as a function of the time after the onset of the release. Therefore, we propose that slowing during isotonic shortening in single isolated smooth muscle cells is the result of an internal load that opposes shortening and increases as cell length decreases.

Effects of myosin kinase inhibiting peptide on contractility and LC20 phosphorylation in skinned smooth muscle

1992 ◽  
Vol 262 (6) ◽  
pp. C1437-C1445 ◽  
Author(s):  
J. D. Strauss ◽  
P. de Lanerolle ◽  
R. J. Paul
Keyword(s):  
Smooth Muscle ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Kinase Inhibitor ◽  
Isometric Force ◽  
Polyacrylamide Gel Electrophoresis ◽  
Competitive Inhibitor ◽  
Myosin Light Chain Phosphorylation ◽  
Taenia Coli ◽  
Shortening Velocity

A peptide inhibitor, myosin kinase inhibitor (MKI), of myosin light chain kinase (MLCK) was tested for its effects on contractility and myosin light chain phosphorylation in Triton X-100 skinned guinea pig taenia coli. MKI is based on the amino acid sequence of the myosin light chain (residues 11-19 LC20) and is a competitive inhibitor [inhibitory constant (Ki) congruent to 10 microM] of purified MLCK with respect to myosin light chain (LC20). MKI inhibited unloaded shortening velocity (V(us)) and the calcium-sensitive ATPase activity of the skinned fibers but had no significant effect on steady-state isometric force or myosin light chain phosphorylation, as measured by IEF-polyacrylamide gel electrophoresis analysis. MKI had no significant effect on V(us) of thiophosphorylated fibers in the absence of calcium. MKI inhibited MLCK activity in protein extracts from taenia coli, as measured by radioactive phosphate incorporation into LC20. Surprisingly, MKI also inhibited the phosphatase activity of these same extracts. This peptide slowed the rate and extent of relaxation of calcium-contracted fibers and elicited a contraction in relaxed fibers. These results are consistent with the hypothesis that MKI may be a phosphatase inhibitor as well as an inhibitor of MLCK. Our data further suggest that the rate of phosphorylation-dephosphorylation turnover may be important in regulating V(us) in smooth muscle.

Effects of calponin on isometric force and shortening velocity in permeabilized taenia coli smooth muscle

1996 ◽  
Vol 270 (2) ◽  
pp. C481-C487 ◽  
Author(s):  
K. Obara ◽  
P. T. Szymanski ◽  
T. Tao ◽  
R. J. Paul
Keyword(s):  
Smooth Muscle ◽  
Light Chain ◽  
Isometric Force ◽  
Dependent Manner ◽  
Taenia Coli ◽  
Shortening Velocity ◽  
Muscle Contractility ◽  
Smooth Muscle Contractility ◽  
Contractile System ◽  
Cross Bridges

Calponin, a thin filament-associated protein, inhibits actomyosin adenosinetriphosphatase in solution and has been suggested to modulate smooth muscle contractility. We used permeabilized guinea pig taenia coli smooth muscle to investigate whether calponin can modulate actin-myosin interaction in a more organized contractile system. Fibers were permeabilized with Triton X-100 and glycerol, which permit access of large macromolecules to the contractile apparatus. For contractures elicited by Ca2+ (6.6 microM + 0.1 microM calmodulin), the recombinant alpha-isoform of chicken gizzard calponin (CaP) decreased isometric force (Fo) and unloaded shortening velocity (Vus) in a dose-dependent manner; 1 microM CaP had minimal effects on force (< 10%) but reduced Vus by approximately 50% and 10 microM CaP reduced Fo to 27% of control and Vus to near zero levels. To eliminate any effects of the binding of calmodulin by CaP and consequent inhibition of myosin light chain kinase activity, we also studied fibers activated by thiophosphorylation of the myosin regulatory light chain. Fo was only moderately inhibited, remaining at approximately 75% of control in the presence of CaP (10 microM), whereas Vus was reduced to 32% of control. A similar inhibition was obtained with a mutant (CaPcys175) that retains the ability to bind to actin. CaP phosphorylated by protein kinase C and CaPcys175 mutant labeled with 1,5-IAEDANS, which bind actin poorly, were not effective inhibitors. Our results indicate that 1) CaP more strongly inhibits Vus (approximately cross-bridge cycle rate) than Fo (approximately number of activated cross bridges) and 2) the effects of CaP are related to its binding to actin. Thus the function of CaP in regulation of smooth muscle contractility may be more strongly related to its function as a modulator of velocity, as related to the "latch state," than as an "on-off" switch.

scholarly journals The effects of inorganic phosphate on muscle force development and energetics: challenges in modelling related to experimental uncertainties

2019 ◽  
Author(s):  
Alf Månsson
Keyword(s):  
Inorganic Phosphate ◽  
Muscle Force ◽  
Isometric Force ◽  
Shortening Velocity ◽  
Apparent Contradiction ◽  
Sequence Of Events ◽  
Velocity Relationship ◽  
Force Velocity ◽  
Cross Bridges ◽  
Experimental Findings

Abstract Muscle force and power are developed by myosin cross-bridges, which cyclically attach to actin, undergo a force-generating transition and detach under turnover of ATP. The force-generating transition is intimately associated with release of inorganic phosphate (Pi) but the exact sequence of events in relation to the actual Pi release step is controversial. Details of this process are reflected in the relationships between [Pi] and the developed force and shortening velocity. In order to account for these relationships, models have proposed branched kinetic pathways or loose coupling between biochemical and force-generating transitions. A key hypothesis underlying the present study is that such complexities are not required to explain changes in the force–velocity relationship and ATP turnover rate with altered [Pi]. We therefore set out to test if models without branched kinetic paths and Pi-release occurring before the main force-generating transition can account for effects of varied [Pi] (0.1–25 mM). The models tested, one assuming either linear or non-linear cross-bridge elasticity, account well for critical aspects of muscle contraction at 0.5 mM Pi but their capacity to account for the maximum power output vary. We find that the models, within experimental uncertainties, account for the relationship between [Pi] and isometric force as well as between [Pi] and the velocity of shortening at low loads. However, in apparent contradiction with available experimental findings, the tested models produce an anomalous force–velocity relationship at elevated [Pi] and high loads with more than one possible velocity for a given load. Nevertheless, considering experimental uncertainties and effects of sarcomere non-uniformities, these discrepancies are insufficient to refute the tested models in favour of more complex alternatives.

Force-Velocity Relationships of a Locust Flight Muscle at Different Times During a Twitch Contraction

1991 ◽  
Vol 159 (1) ◽  
pp. 65-87 ◽  
Author(s):  
JEAN G. MALAMUD ◽  
ROBERT K. JOSEPHSON
Keyword(s):  
Flight Muscle ◽  
Isometric Force ◽  
Velocity Curve ◽  
Shortening Velocity ◽  
Single Twitch ◽  
Emory University ◽  
Generating Capacity ◽  
Force Velocity ◽  
Maximum Isometric Force ◽  
Isometric Twitch

The force-velocity relationships during isotonic shortening were determined for the metathoracic second tergocoxal muscle of the locust Schistocerca americana (Drury). This muscle is a synchronous flight muscle. During the plateau of a tetanic contraction, the maximum shortening velocity (Vmax) determined from the force-velocity curve was 5.2 muscle lengths s−1 (25°C) and the curvature (a/Po) was 0.62. The maximum isometric force (P0) was 36.3 N cm−2. Early in a twitch (at times shorter than the isometric twitch rise time) the values for Vmax and curvature were similar to those during the tetanic plateau, but the curves at different times during the twitch intercepted the force axis at values less than P0. Later in the twitch, Vmax declined. A variable termed degree of activation (DA) is developed as a measure of the force-generating capacity of a muscle when this may be time-varying, as throughout most of a twitch. DA is determined from the shortening velocity at an intermediate load and is the predicted intercept of the force-velocity curve with the force axis relative to the tetanic intercept. In the locust muscle, DA rose to a maximum in 2–3 ms after the end of the latent period. DA reached 80° of the tetanic value during a single twitch; during the second twitch of a pair, the peak DA reached approximately the tetanic value. After a brief plateau, DA declined approximately exponentially. The time constant of DA decay was about 14 ms. Note: Present address: Department of Physiology, Emory University, Atlanta, GA30322, USA.

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