Mechanical alterations in sensitized canine saphenous vein

1990 ◽  
Vol 69 (1) ◽  
pp. 171-178 ◽  
Author(s):  
Z. Wang ◽  
C. Y. Seow ◽  
W. Kepron ◽  
N. L. Stephens
Keyword(s):  
Smooth Muscle ◽  
Saphenous Vein ◽  
Specific Antigen ◽  
Isometric Tension ◽  
Antigen Challenge ◽  
Pollen Extract ◽  
Shortening Velocity ◽  
Tension Development ◽  
Cycling Rate ◽  
Cross Bridge

Because it is likely that antigen sensitization is not restricted to airway smooth muscle but probably involves all tissues in the animal, we decided to test the hypothesis that saphenous vein from pollen extract-sensitized dogs is sensitized and is, in addition, mechanically altered. To this end, we studied responses to specific antigen challenge and length-tension and force-velocity relationships in sensitized (SSV) and control saphenous veins (CSV). The antigen challenge revealed that the venous smooth muscle was strongly sensitized and developed a Schultz-Dale response, the two main mediators of which were histamine and norepinephrine. Length-tension relationship studies showed that whereas there is no difference in maximum isometric tension development between SSV and CSV [93.95 +/- 7.34 and 87.86 +/- 4.00 (SE) mN/mm2, respectively], SSV exhibited a significantly greater maximum isotonic shortening capacity of 0.613 +/- 0.009 optional length (lo) vs. 0.578 +/- 0.012 lo for CSV. Unloaded shortening velocity (Vo), which reflects the cross-bridge cycling rate, was determined at different times after the onset of electrical stimulation. Maximum Vo was attained early (5 s) in the contraction; a 15% decline in Vo was observed at the plateau of the contraction (15 s). At 5 s, Vo of SSV (0.316 +/- 0.019 lo/s) was significantly higher than that of CSV (0.269 +/- 0.018 lo/s), although Vos were same at 15 (0.249 +/- 0.021 lo/s for SSV and 0.237 +/- 0.019 lo/s for CSV). The increase in shortening likely results from th e increase in the early cross-bridge cycling rate because our studies show that the bulk of shortening occurs in the first 5 s.(ABSTRACT TRUNCATED AT 250 WORDS)

Relaxation of smooth muscle

1994 ◽  
Vol 72 (11) ◽  
pp. 1345-1350 ◽  
Author(s):  
N. L. Stephens ◽  
H. Jiang
Keyword(s):  
Smooth Muscle ◽  
Muscle Relaxation ◽  
Late Phase ◽  
Contractile Element ◽  
Smooth Muscle Relaxation ◽  
Shortening Velocity ◽  
Cycling Rate ◽  
Cross Bridge ◽  
Cross Bridges ◽  
And Control

We have demonstrated that in dogs antigen sensitization results in alterations of contractile properties. These changes could account for the hyperresponsiveness reported in asthma. The failure of the muscle to relax could be another important factor responsible for maintaining high airway resistance. We therefore developed an index of isotonic relaxation, t1/2,CE (half time for relaxation that is independent of muscle load and initial contractile element length), for evaluation of the relaxation process. Because the maximum shortening velocity at 2 s but not at 10 s was greater in sensitized bronchial smooth muscle than that in controls, studies of relaxation were also undertaken at these two times. The mean half-relaxation time indicated by t1/2,CE showed no difference between sensitized and control muscles after 10 s of stimulation (8.38 ± 0.92 vs. 7.78 ± 0.93 s, means ± SE); however, it was prolonged significantly in the sensitized muscle only stimulated for 1 s (12.74 ± 2.5 s, mean ± SE) compared with the control (6.98 ± 1.01 s). During the late phase of isotonic relaxation, both groups showed an unexpected spontaneous increase in zero-load shortening velocity, which is an index of cross-bridge cycling rate. We conclude that (i) both contraction and relaxation properties of early normally cycling cross bridges are altered after sensitization and these changes may account for the hyperresponsiveness observed in asthmatics and (ii) the cross-bridge cycling rate increases spontaneously during isotonic relaxation, probably as a result of reactivation of the contractile mechanism.Key words: smooth muscle relaxation, isotonic relaxation, spontaneous activation in late relaxation, mechanisms for airway hyperresponsiveness, new index of muscle relaxation.

Oxytocin-mediated recruitment of slowly cycling cross bridges and isometric force in rat myometrium

1996 ◽  
Vol 270 (2) ◽  
pp. E203-E208
Author(s):  
A. L. Ruzycky ◽  
B. T. Ameredes
Keyword(s):  
Isometric Force ◽  
Additional Stress ◽  
Shortening Velocity ◽  
Cycling Rate ◽  
Quick Release ◽  
Cross Bridge ◽  
Cross Bridges ◽  
Unit Stress ◽  
Release Method ◽  
The Relationship

The relationship between cross-bridge cycling rate and isometric stress was investigated in rat myometrium. Stress production by myometrial strips was measured under resting, K+ depolarization, and oxytocin-stimulated conditions. Cross-bridge cycling rates were determined from measurements of maximal unloaded shortening velocity, using the quick-release method. Force redevelopment after the quick release was used as an index of cross-bridge attachment. With maximal K+ stimulation, stress increased with increased cross-bridge cycling (+76%; P < 0.05) and attached cross bridges (+112%; P < 0.05). Addition of oxytocin during K+ stimulation further increased stress (+30%; P < 0.05). With this force component, the cross-bridge cycling rate decreased (-60%; P < 0.05) similar to that under resting conditions. Attached cross-bridges did not increase with this additional stress. The results suggest two distinct mechanisms mediating myometrial contractions. One requires elevated intracellular calcium and rapidly cycling cross bridges. The other mechanism may be independent of calcium and appears to be mediated by slowly cycling cross bridges, supporting greater unit stress.

Regulation of shortening velocity by cross-bridge phosphorylation in smooth muscle

1988 ◽  
Vol 255 (1) ◽  
pp. C86-C94 ◽  
Author(s):  
C. M. Hai ◽  
R. A. Murphy
Keyword(s):  
Smooth Muscle ◽  
Shortening Velocity ◽  
Internal Load ◽  
Cross Bridge ◽  
Bridge Model ◽  
The Family ◽  
Cross Bridges ◽  
Latch State ◽  
The Relationship ◽  
State Stress

We have proposed a model that incorporates a dephosphorylated "latch bridge" to explain the mechanics and energetics of smooth muscle. Cross-bridge phosphorylation is proposed as a prerequisite for cross-bridge attachment and rapid cycling. Features of the model are 1) myosin light chain kinase and phosphatase can act on both free and attached cross bridges, 2) dephosphorylation of an attached phosphorylated cross bridge produces a noncycling "latch bridge," and 3) latch bridges have a slow detachment rate. This model quantitatively predicts the latch state: stress maintenance with reduced phosphorylation, cross-bridge cycling rates, and ATP consumption. In this study, we adapted A. F. Huxley's formulation of crossbridge cycling (A. F. Huxley, Progr. Biophys. Mol. Biol. 7: 255-318, 1957) to the latch-bridge model to predict the relationship between isotonic shortening velocity and phosphorylation. The model successfully predicted the linear dependence of maximum shortening velocity at zero external load (V0) on phosphorylation, as well as the family of stress-velocity curves determined at different times during a contraction when phosphorylation values varied. The model implies that it is unnecessary to invoke an internal load or multiple regulatory mechanisms to explain regulation of V0 in smooth muscle.

scholarly journals Friction in airway smooth muscle: mechanism, latch, and implications in asthma

1996 ◽  
Vol 81 (6) ◽  
pp. 2703-2703 ◽  
Author(s):  
J. J. Fredberg ◽  
K. A. Jones ◽  
M. Nathan ◽  
S. Raboudi ◽  
Y. S. Prakash ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Time Course ◽  
Molecular Mechanisms ◽  
Mechanical Energy ◽  
Frictional Stress ◽  
Turnover Rates ◽  
Shortening Velocity ◽  
Biphasic Pattern ◽  
Cross Bridge

Fredberg, J. J., K. A. Jones, M. Nathan, S. Raboudi, Y. S. Prakash, S. A. Shore, J. P. Butler, and G. C. Sieck. Friction in airway smooth muscle: mechanism, latch, and implications in asthma. J. Appl. Physiol. 81(6): 2703–2712, 1996.—In muscle, active force and stiffness reflect numbers of actin-myosin interactions and shortening velocity reflects their turnover rates, but the molecular basis of mechanical friction is somewhat less clear. To better characterize molecular mechanisms that govern mechanical friction, we measured the rate of mechanical energy dissipation and the rate of actomyosin ATP utilization simultaneously in activated canine airway smooth muscle subjected to small periodic stretches as occur in breathing. The amplitude of the frictional stress is proportional to ηE, where E is the tissue stiffness defined by the slope of the resulting force vs. displacement loop and η is the hysteresivity defined by the fatness of that loop. From contractile stimulus onset, the time course of frictional stress amplitude followed a biphasic pattern that tracked that of the rate of actomyosin ATP consumption. The time course of hysteresivity, however, followed a different biphasic pattern that tracked that of shortening velocity. Taken together with an analysis of mechanical energy storage and dissipation in the cross-bridge cycle, these results indicate, first, that like shortening velocity and the rate of actomyosin ATP utilization, mechanical friction in airway smooth muscle is also governed by the rate of cross-bridge cycling; second, that changes in cycling rate associated with conversion of rapidly cycling cross bridges to slowly cycling latch bridges can be assessed from changes of hysteresivity of the force vs. displacement loop; and third, that steady-state force maintenance (latch) is a low-friction contractile state. This last finding may account for the unique inability of asthmatic patients to reverse spontaneous airways obstruction with a deep inspiration.

scholarly journals Series-to-parallel transition in the filament lattice of airway smooth muscle

2000 ◽  
Vol 89 (3) ◽  
pp. 869-876 ◽  
Author(s):  
Chun Y. Seow ◽  
Victor R. Pratusevich ◽  
Lincoln E. Ford
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Muscle Length ◽  
Thick Filament ◽  
Cycling Rate ◽  
Cross Bridge ◽  
Parallel Change ◽  
Force Velocity ◽  
Cross Bridges ◽  
Trachealis Muscle

Force-velocity curves measured at different times during tetani of sheep trachealis muscle were analyzed to assess whether velocity slowing could be explained by thick-filament lengthening. Such lengthening increases force by placing more cross bridges in parallel on longer filaments and decreases velocity by reducing the number of filaments spanning muscle length. From 2 s after the onset of stimulation, when force had achieved 42% of it final value, to 28 s, when force had been at its tetanic plateau for ∼15 s, velocity decreases were exactly matched by force increases when force was adjusted for changes in activation, as assessed from the maximum power value in the force-velocity curves. A twofold change in velocity could be quantitatively explained by a series-to-parallel change in the filament lattice without any need to postulate a change in cross-bridge cycling rate.

Yersinia enterocolitica enteritis affects rabbit intestinal longitudinal smooth muscle function

1992 ◽  
Vol 262 (2) ◽  
pp. G278-G284 ◽  
Author(s):  
R. B. Scott ◽  
D. T. Tan
Keyword(s):  
Smooth Muscle ◽  
Weight Gain ◽  
Food Intake ◽  
Yersinia Enterocolitica ◽  
Biomechanical Properties ◽  
Isometric Tension ◽  
Infected Group ◽  
Tension Development ◽  
Longitudinal Smooth Muscle ◽  
Tension Curves

To determine whether Yersinia enterocolitica (YE) enteritis has an effect on the biomechanical properties of intestinal smooth muscle, New Zealand White rabbits (600-900 g) were divided into an infected group (n = 9) and sham-infected animals fed ad libitum (n = 9), or pair fed with the infected group (n = 9). Animals were inoculated with 10(10) organisms of YE in 10 ml NaHCO3 (infected group) or 10 ml NaHCO3 (sham-infected control and pair-fed groups) at time 0. Daily food intake, weight gain, and YE excretion were noted. Six days later animals were killed and longitudinal smooth muscle strips prepared from proximal (P), medial (M), and distal (D) segments of intestine in each treatment group. Isometric tension was recorded in tissue baths perfused with oxygenated Krebs solution and 10(-6) M tetrodotoxin. Basal and active (the response to 10(-5) M carbachol) length-tension curves were generated. Then, with the muscle strips stretched to their optimum length for tension development, the dose response to carbachol and to graded depolarization with KCl was determined. Infected animals had a significantly reduced food intake and weight gain compared with controls. The development of basal tension with stretch was not significantly different in infected compared with control or pair-fed tissues from the same site.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Effect of denervation on ATP consumption rate of diaphragm muscle fibers

2007 ◽  
Vol 103 (3) ◽  
pp. 858-866 ◽  
Author(s):  
Gary C. Sieck ◽  
Wen-Zhi Zhan ◽  
Young-Soo Han ◽  
Y. S. Prakash
Keyword(s):  
Consumption Rate ◽  
Atp Hydrolysis ◽  
Maximum Velocity ◽  
Diaphragm Muscle ◽  
Single Type ◽  
Shortening Velocity ◽  
Cycling Rate ◽  
Cross Bridge ◽  
Atpase Reaction ◽  
The Difference

Denervation (DNV) of rat diaphragm muscle (DIAm) decreases myosin heavy chain (MHC) content in fibers expressing MHC2X isoform but not in fibers expressing MHCslow and MHC2A. Since MHC is the site of ATP hydrolysis during muscle contraction, we hypothesized that ATP consumption rate during maximum isometric activation (ATPiso) is reduced following unilateral DIAm DNV and that this effect is most pronounced in fibers expressing MHC2X. In single-type-identified, permeabilized DIAm fibers, ATPiso was measured using NADH-linked fluorometry. The maximum velocity of the actomyosin ATPase reaction ( Vmax ATPase) was determined using quantitative histochemistry. The effect of DNV on maximum unloaded shortening velocity ( Vo) and cross-bridge cycling rate [estimated from the rate constant for force redevelopment ( kTR) following quick release and restretch] was also examined. Two weeks after DNV, ATPiso was significantly reduced in fibers expressing MHC2X, but unaffected in fibers expressing MHCslow and MHC2A. This effect of DNV on fibers expressing MHC2X persisted even after normalization for DNV-induced reduction in MHC content. With DNV, Vo and kTR were slowed in fibers expressing MHC2X, consistent with the effect on ATPiso. The difference between Vmax ATPase and ATPiso reflects reserve capacity for ATP consumption, which was reduced across all fibers following DNV; however, this effect was most pronounced in fibers expressing MHC2X. DNV-induced reductions in ATPiso and Vmax ATPase of fibers expressing MHC2X reflect the underlying decrease in MHC content, while reduction in ATPiso also reflects a slowing of cross-bridge cycling rate.

scholarly journals The latch-bridge hypothesis of smooth muscle contraction

2005 ◽  
Vol 83 (10) ◽  
pp. 857-864 ◽  
Author(s):  
Richard A Murphy ◽  
Christopher M Rembold
Keyword(s):  
Smooth Muscle ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Striated Muscle ◽  
Smooth Muscle Contraction ◽  
Myosin Light Chain Phosphatase ◽  
Shortening Velocity ◽  
General Applicability ◽  
Cross Bridge ◽  
Mechanical Transduction

In contrast to striated muscle, both normalized force and shortening velocities are regulated functions of cross-bridge phosphorylation in smooth muscle. Physiologically this is manifested as relatively fast rates of contraction associated with transiently high levels of cross-bridge phosphorylation. In sustained contractions, Ca2+, cross-bridge phosphorylation, and ATP consumption rates fall, a phenomenon termed "latch". This review focuses on the Hai and Murphy (1988a) model that predicted the highly non-linear dependence of force on phosphorylation and a directly proportional dependence of shortening velocity on phosphorylation. This model hypothesized that (i) cross-bridge phosphorylation was obligatory for cross-bridge attachment, but also that (ii) dephosphorylation of an attached cross-bridge reduced its detachment rate. The resulting variety of cross-bridge cycles as predicted by the model could explain the observed dependencies of force and velocity on cross-bridge phosphorylation. New evidence supports modifications for more general applicability. First, myosin light chain phosphatase activity is regulated. Activation of myosin phosphatase is best demonstrated with inhibitory regulatory mechanisms acting via nitric oxide. The second modification of the model incorporates cooperativity in cross-bridge attachment to predict improved data on the dependence of force on phosphorylation. The molecular basis for cooperativity is unknown, but may involve thin filament proteins absent in striated muscle.Key words: chemo-mechanical transduction, activation-contraction coupling, cross-bridge, myosin light chain kinase, myosin light chain phosphatase, phosphorylation, cooperativity.

Stiffness of active smooth muscle during forced elongation

1987 ◽  
Vol 253 (3) ◽  
pp. C484-C493 ◽  
Author(s):  
R. A. Meiss
Keyword(s):  
Smooth Muscle ◽  
Phase Angle ◽  
Muscle Length ◽  
Isometric Tension ◽  
Microcomputer System ◽  
Tension Development ◽  
Stretch Rate ◽  
Angle Data ◽  
Cross Bridges ◽  
System Phase

The stiffness of isometrically contracting mesotubarium superius and ovarian ligament smooth muscle from estrous female rabbits was measured continuously by using sinusoidal length perturbations (at 80 Hz, less than 15 microns peak to peak). Muscles were stimulated with alternating current fields, and all records were digitized using a microcomputer system. Phase-angle data were used to resolve computed stiffness into elastic and viscous components. Stiffness measurements were continued during long ramp-type stretches (up to 25% of muscle length) delivered as soon as force was maximal. To use the period of isometric tension development as a standard for comparison, the expected stiffness was computed during the long stretch. Stiffness was reduced in approximate proportion to the ramp stretch rate, and the reduction was confined largely to the elastic component. Cooling the muscle increased the stiffness deviation at a given stretch rate. It is proposed that the long stretch detaches cross bridges that can reattach to new sites as myofilaments shear past one another. At higher shearing speeds, less time is available for reattachment and stiffness is further reduced.

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