Force Maintenance with Reduced Ability to Shorten Actively in Barnacle Striated Muscle

1990 ◽  
Vol 148 (1) ◽  
pp. 281-291
Author(s):  
H. IWAMOTO ◽  
A. MURAOKA ◽  
A. GOTO ◽  
H. SUGI
Keyword(s):  
Electrical Stimulation ◽  
Mechanical Response ◽  
Striated Muscle ◽  
Isometric Force ◽  
Shortening Velocity ◽  
Cycling Rate ◽  
Quick Release ◽  
Mechanical Responses ◽  
Cross Bridge ◽  
Force Maintenance

1. Fibres from adductor scutorum muscle of a barnacle Tetraclita squamosa were made to contract isometrically by electrical stimulation, and the change in the ability to shorten actively during the mechanical responses was examined by suddenly allowing the fibres to shorten under a very small load (<3 % of the force immediately before shortening) at various times after the onset of stimulation. 2. The shortening velocity (Vsl) was nearly constant during stimulation. After the cessation of stimulation, shortening velocity decreased steeply while isometric force decayed slowly, indicating that isometric force was maintained with reduced ability to shorten actively. 3. Similar results were obtained when the maximum rate of force redevelopment following a quick release was measured at various times during the mechanical response to electrical stimulation. 4. In these fibres, but not in fibres from frog skeletal muscle, a quick restretch following a quick release could restore the force to a level similar to that observed without a quick release. These results, together with those above, indicated a reduced cross-bridge cycling rate during the relaxation phase of mechanical responses of barnacle fibres to electrical stimulation. 5. During electrical stimulation, Vsl showed less dependence on [Ca2+]o than was shown by isometric force. 6. These results are discussed in connection with the mechanism of force maintenance with reduced cross-bridge cycling rate.

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.

Inorganic phosphate speeds loaded shortening in rat skinned cardiac myocytes

2004 ◽  
Vol 287 (2) ◽  
pp. C500-C507 ◽  
Author(s):  
Aaron C. Hinken ◽  
Kerry S. McDonald
Keyword(s):  
Cardiac Myocytes ◽  
Power Output ◽  
Inorganic Phosphate ◽  
Striated Muscle ◽  
Isometric Force ◽  
Force Transducer ◽  
Shortening Velocity ◽  
Cross Bridge ◽  
Force Peak ◽  
The Cross

Force generation in striated muscle is coupled with inorganic phosphate (Pi) release from myosin, because force falls with increasing Pi concentration ([Pi]). However, it is unclear which steps in the cross-bridge cycle limit loaded shortening and power output. We examined the role of Pi in determining force, unloaded and loaded shortening, power output, and rate of force development in rat skinned cardiac myocytes to discern which step in the cross-bridge cycle limits loaded shortening. Myocytes ( n = 6) were attached between a force transducer and position motor, and contractile properties were measured over a range of loads during maximal Ca2+ activation. Addition of 5 mM Pi had no effect on maximal unloaded shortening velocity ( Vo) (control 1.83 ± 0.75, 5 mM added Pi 1.75 ± 0.58 muscle lengths/s; n = 6). Conversely, addition of 2.5, 5, and 10 mM Pi progressively decreased force but resulted in faster loaded shortening and greater power output (when normalized for the decrease in force) at all loads greater than ∼10% isometric force. Peak normalized power output increased 16% with 2.5 mM added Pi and further increased to a plateau of ∼35% with 5 and 10 mM added Pi. Interestingly, the rate constant of force redevelopment ( ktr) progressively increased from 0 to 10 mM added Pi, with ktr ∼360% greater at 10 mM than at 0 mM added Pi. Overall, these results suggest that the Pi release step in the cross-bridge cycle is rate limiting for determining shortening velocity and power output at intermediate and high relative loads in cardiac myocytes.

scholarly journals Are Force Enhancement after Stretch and Muscle Fatigue Due to Effects of Elevated Inorganic Phosphate and Low Calcium on Cross Bridge Kinetics?

Medicina ◽  
2020 ◽  
Vol 56 (5) ◽  
pp. 249
Author(s):  
Hans Degens ◽  
David A. Jones
Keyword(s):  
Muscle Fatigue ◽  
Isometric Force ◽  
Force Enhancement ◽  
Shortening Velocity ◽  
Cross Bridge ◽  
Fatigued Muscle ◽  
Butanedione Monoxime ◽  
Combined Action ◽  
Cross Bridges ◽  
Muscle Contractile

Background and Objectives: Muscle fatigue is characterised by (1) loss of force, (2) decreased maximal shortening velocity and (3) a greater resistance to stretch that could be due to reduced intracellular Ca2+ and increased Pi, which alter cross bridge kinetics. Materials and Methods: To investigate this, we used (1) 2,3-butanedione monoxime (BDM), believed to increase the proportion of attached but non-force-generating cross bridges; (2) Pi that increases the proportion of attached cross bridges, but with Pi still attached; and (3) reduced activating Ca2+. We used permeabilised rat soleus fibres, activated with pCa 4.5 at 15 °C. Results: The addition of 1 mM BDM or 15 mM Pi, or the lowering of the Ca2+ to pCa 5.5, all reduced the isometric force by around 50%. Stiffness decreased in proportion to isometric force when the fibres were activated at pCa 5.5, but was well maintained in the presence of Pi and BDM. Force enhancement after a stretch increased with the length of stretch and Pi, suggesting a role for titin. Maximum shortening velocity was reduced by about 50% in the presence of BDM and pCa 5.5, but was slightly increased by Pi. Neither decreasing Ca2+ nor increasing Pi alone mimicked the effects of fatigue on muscle contractile characteristics entirely. Only BDM elicited a decrease of force and slowing with maintained stiffness, similar to the situation in fatigued muscle. Conclusions: This suggests that in fatigue, there is an accumulation of attached but low-force cross bridges that cannot be the result of the combined action of reduced Ca2+ or increased Pi alone, but is probably due to a combination of factors that change during fatigue.

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 Active shortening protects against stretch-induced force deficits in human skeletal muscle

2017 ◽  
Vol 122 (5) ◽  
pp. 1218-1226 ◽  
Author(s):  
Anjali L. Saripalli ◽  
Kristoffer B. Sugg ◽  
Christopher L. Mendias ◽  
Susan V. Brooks ◽  
Dennis R. Claflin
Keyword(s):  
Skeletal Muscle ◽  
High Velocity ◽  
Isometric Force ◽  
Human Subjects ◽  
Causative Factor ◽  
Negative Consequences ◽  
Shortening Velocity ◽  
Contracting Muscle ◽  
Working Hypothesis ◽  
Force Maintenance

Skeletal muscle contraction results from molecular interactions of myosin “crossbridges” with adjacent actin filament binding sites. The binding of myosin to actin can be “weak” or “strong,” and only strong binding states contribute to force production. During active shortening, the number of strongly bound crossbridges declines with increasing shortening velocity. Forcibly stretching a muscle that is actively shortening at high velocity results in no apparent negative consequences, whereas stretch of an isometrically (fixed-length) contracting muscle causes ultrastructural damage and a decline in force-generating capability. Our working hypothesis is that stretch-induced damage is uniquely attributable to the population of crossbridges that are strongly bound. We tested the hypothesis that stretch-induced force deficits decline as the prevailing shortening velocity is increased. Experiments were performed on permeabilized segments of individual skeletal muscle fibers obtained from human subjects. Fibers were maximally activated and allowed either to generate maximum isometric force (Fo), or to shorten at velocities that resulted in force maintenance of ≈50% Fo or ≈2% Fo. For each test condition, a rapid stretch equivalent to 0.1 × optimal fiber length was applied. Relative to prestretch Fo, force deficits resulting from stretches applied during force maintenance of 100, ≈50, and ≈2% Fo were 23.2 ± 8.6, 7.8 ± 4.2, and 0.3 ± 3.3%, respectively (means ± SD, n = 20). We conclude that stretch-induced damage declines with increasing shortening velocity, consistent with the working hypothesis that the fraction of strongly bound crossbridges is a causative factor in the susceptibility of skeletal muscle to stretch-induced damage. NEW & NOTEWORTHY Force deficits caused by stretch of contracting muscle are most severe when the stretch is applied during an isometric contraction, but prevented if the muscle is shortening at high velocity when the stretch occurs. This study indicates that velocity-controlled modulation of the number of strongly bound crossbridges is the basis for the observed relationship between stretch-induced muscle damage and prevailing shortening velocity.

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.

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.

Myosin phosphorylation and calcium in tonic and phasic contractions of colonic smooth muscle

1991 ◽  
Vol 260 (6) ◽  
pp. G958-G964 ◽  
Author(s):  
W. T. Gerthoffer ◽  
K. A. Murphey ◽  
J. Mangini ◽  
S. Boman ◽  
F. A. Lattanzio
Keyword(s):  
Smooth Muscle ◽  
Time Dependence ◽  
Fluorescence Intensity ◽  
Light Chain ◽  
Proximal Colon ◽  
Shortening Velocity ◽  
Myosin Phosphorylation ◽  
Quick Release ◽  
Circular Smooth Muscle ◽  
Cross Bridge

The time dependence of lightly loaded shortening velocity, myosin phosphorylation, and changes in myoplasmic Ca2+ concentration ([Ca2+]i) were measured during tonic and phasic contractions of circular smooth muscle from the proximal colon of the dog. Shortening velocity was measured by quick release to a 10% afterload. Myosin phosphorylation was measured by an immunoblot method, and changes in [Ca2+]i were estimated by measuring fluorescence intensity at 550 nm in muscle strips loaded with fluo-3. During tonic contractions induced by 60 mM K+, phosphorylation increased monotonically from 0.11 +/- 0.011 to 0.29 +/- 0.015 mol Pi/mol light chain at 10 min. In contrast, lightly loaded shortening velocity increased rapidly within 10 s to 0.042 +/- 0.003 lengths/s and decreased exponentially to 0.013 +/- 0.001 lengths/s at 15 min. During transient contractions induced by 100 microM acetylcholine, phosphorylation increased from 0.16 +/- 0.03 to 0.30 +/- 0.06 mol Pi/mol light chain at 19 s. In contrast, shortening velocity increased to 0.068 +/- 0.015 lengths/s within 2.4 s and decreased significantly to 0.027 +/- 0.009 lengths/s at 22 s. Fluo-3 fluorescence increased in parallel with force during both tonic and transient contractions. In a smooth muscle that is able to contract both tonically and phasically we observed transient increases in shortening velocity without concurrent phosphorylation or [Ca2+]i transients. Therefore, there are factors in addition to myosin phosphorylation or changes in [Ca2+]i that regulate cross-bridge cycling rates in both tonic and phasic contractions.

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)

Similar effects of cooling and fatigue on eccentric and concentric force-velocity relationships in human muscle

2001 ◽  
Vol 90 (6) ◽  
pp. 2109-2116 ◽  
Author(s):  
C. J. De Ruiter ◽  
A. De Haan
Keyword(s):  
Isometric Force ◽  
Human Muscle ◽  
Muscle Temperature ◽  
Adductor Pollicis Muscle ◽  
Concentric Contractions ◽  
Cycling Rate ◽  
Concentric Force ◽  
Cross Bridge ◽  
Different Temperatures ◽  
Force Velocity

The purpose of this study was to investigate the effects of muscle temperature and fatigue during stretch (eccentric) and shortening (concentric) contractions of the maximally electrically activated human adductor pollicis muscle. After immersion of the lower arm in water baths of four different temperatures, the calculated muscle temperatures were 36.8, 31.6, 26.6, and 22.3°C. Normalized (isometric force = 100%) eccentric force increased with stretch velocity to maximal values of 136.4 ± 1.6 and 162.1 ± 2.0% at 36.8 and 22.3°C, respectively. After repetitive ischemic concentric contractions, fatigue was less at the lower temperatures, and at all temperatures the loss of eccentric force was smaller than the loss of isometric and concentric force. Consequently, normalized eccentric forces increased during fatigue to 159.7 ± 4.6 and 185.7 ± 7.3% at 36.8 and 22.3°C, respectively. Maximal normalized eccentric force increased exponentially ( r 2 = 0.95) when V max was reduced by cooling and/or fatiguing contractions. This may indicate that a reduction in cross-bridge cycling rate could underlie the significant increases in normalized eccentric force found with cooling and fatigue.

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