Heat production of rat anococcygeus muscle during isometric contraction

1988 ◽  
Vol 255 (4) ◽  
pp. C536-C542 ◽  
Author(s):  
J. S. Walker ◽  
I. R. Wendt ◽  
C. L. Gibbs
Keyword(s):  
Energy Expenditure ◽  
Heat Production ◽  
Progressive Increase ◽  
Isometric Contractions ◽  
Shortening Velocity ◽  
Anococcygeus Muscle ◽  
Cross Bridge ◽  
Time Integral ◽  
Rat Anococcygeus Muscle ◽  
Cross Bridges

Heat production, unloaded shortening velocity (Vus), and load-bearing capacity (LBC) were studied in the isolated rat anococcygeus muscle during isometric contractions at 27 degrees C. The relation between the total suprabasal heat produced and the stress-time integral for isometric contractions of various durations was curvilinear, demonstrating a decreasing slope as contractile duration increased. The rate of heat production at 600 s was approximately 68% of the peak value of 6.55 mW/g that occurred at 10 s. At the same time, force rose from a mean of 92 mN/mm2 at 10 s to a value of 140 mN/mm2 at 600 s. This produced a nearly threefold increase in the economy of force maintenance. The decline in the rate of heat production was accompanied by a decline in Vus from 0.56 Lo/s at 10 s to 0.28 Lo/s at 600 s, where Lo is the length for optimal force development. This suggests the fall in the rate of heat production was caused, at least in part, by a slowing of cross-bridge kinetics. The ratio of LBC to developed tension at 10 s was not significantly different from the ratio at 600 s, suggesting that the increase in tension was due to an increased number of attached cross bridges. The decline in heat production, therefore, appears contradictory, since an increased number of attached cross bridges would predict an increased rate of energy expenditure. The observations can be reconciled if either 1) the increase in force is caused by a progressive increase in the attachment time of a constant number of cross bridges that cycle at a lower frequency or 2) the decline in energy expenditure caused by the slowing of cross-bridge cycling is sufficient to mask the increase caused by the recruitment of additional cross bridges.

Regulation of energy consumption in cardiac muscle: analysis of isometric contractions

1999 ◽  
Vol 276 (3) ◽  
pp. H998-H1011 ◽  
Author(s):  
Amir Landesberg ◽  
Samuel Sideman
Keyword(s):  
Energy Consumption ◽  
Cardiac Muscle ◽  
Feedback Mechanism ◽  
Isometric Contractions ◽  
Cross Bridge ◽  
Time Integral ◽  
Length Relationship ◽  
Cross Bridges ◽  
Force Time ◽  
Force Time Integral

The well-known linear relationship between oxygen consumption and force-length area or the force-time integral is analyzed here for isometric contractions. The analysis, which is based on a biochemical model that couples calcium kinetics with cross-bridge cycling, indicates that the change in the number of force-generating cross bridges with the change in the sarcomere length depends on the force generated by the cross bridges. This positive-feedback phenomenon is consistent with our reported cooperativity mechanism, whereby the affinity of the troponin for calcium and, hence, cross-bridge recruitment depends on the number of force-generating cross bridges. Moreover, it is demonstrated that a model that does not include a feedback mechanism cannot describe the dependence of energy consumption on the loading conditions. The cooperativity mechanism, which has been shown to determine the force-length relationship and the related Frank-Starling law, is shown here to provide the basis for the regulation of energy consumption in the cardiac muscle.

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 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 Pi on unloaded shortening velocity of slow and fast mammalian muscle fibers

2002 ◽  
Vol 282 (4) ◽  
pp. C647-C653 ◽  
Author(s):  
Jeffrey J. Widrick
Keyword(s):  
Fiber Type ◽  
Muscle Fibers ◽  
Medial Gastrocnemius ◽  
Type I ◽  
Shortening Velocity ◽  
Cross Bridge ◽  
Skinned Muscle ◽  
Specific Effects ◽  
Cross Bridges ◽  
Bridge Models

Chemically skinned muscle fibers, prepared from the rat medial gastrocnemius and soleus, were subjected to four sequential slack tests in Ca2+-activating solutions containing 0, 15, 30, and 0 mM added Pi. Pi (15 and 30 mM) had no effect on the unloaded shortening velocity ( V o) of fibers expressing type IIb myosin heavy chain (MHC). For fibers expressing type I MHC, 15 mM Pi did not alter V o, whereas 30 mM Pireduced V o to 81 ± 1% of the original 0 mM Pi value. This effect was readily reversible when Pi was lowered back to 0 mM. These results are not compatible with current cross-bridge models, developed exclusively from data obtained from fast fibers, in which V o is independent of Pi. The response of the type I fibers at 30 mM Pi is most likely the result of increased internal drag opposing fiber shortening resulting from fiber type-specific effects of Pi on cross bridges, the thin filament, or the rate-limiting step of the cross-bridge cycle.

Mechanical regulation of cardiac muscle by coupling calcium kinetics with cross-bridge cycling: a dynamic model

1994 ◽  
Vol 267 (2) ◽  
pp. H779-H795 ◽  
Author(s):  
A. Landesberg ◽  
S. Sideman
Keyword(s):  
Cardiac Muscle ◽  
Calcium Binding ◽  
Mechanical Activity ◽  
Free Calcium ◽  
Shortening Velocity ◽  
Cross Bridge ◽  
Mechanical Constraints ◽  
Force Velocity ◽  
Cross Bridges ◽  
Reported Data

This study describes the regulation of mechanical activity in the intact cardiac muscle, the effects of the free calcium transients and the mechanical constraints, and emphasizes the central role of the troponin complex in regulating muscle activity. A “loose coupling” between calcium binding to troponin and cross-bridge cycling is stipulated, allowing the existence of cross bridges in the strong conformation without having bound calcium on the neighboring troponin. The model includes two feedback mechanisms: 1) a positive feedback, or cooperativity, in which the cycling cross bridges affect the affinity of troponin for calcium, and 2) a negative mechanical feedback, where the filament-sliding velocity affects cross-bridge cycling. The model simulates the reported experimental force-length and force-velocity relationships at different levels of activation. The dependence of the shortening velocity on calcium concentration, sarcomere length, internal load, and rate of cross-bridge cycling is described analytically in agreement with reported data. Furthermore, the model provides an analytic solution for Hill's equation of the force-velocity relationship and for the phenomena of unloaded shortening velocity and force deficit. The model-calculated changes in free calcium in various mechanical conditions are in good agreement with the available experimental results.

Myosin phosphorylation and regulation of cross-bridge cycle in tracheal smooth muscle

1983 ◽  
Vol 244 (3) ◽  
pp. C182-C187 ◽  
Author(s):  
W. T. Gerthoffer ◽  
R. A. Murphy
Keyword(s):  
Smooth Muscle ◽  
Tracheal Smooth Muscle ◽  
Shortening Velocity ◽  
Active Stress ◽  
Myosin Phosphorylation ◽  
Cross Bridge ◽  
Rapid Changes ◽  
Cross Bridges ◽  
Resting Muscle ◽  
Isotonic Shortening

We have tested the hypothesis that phosphorylation of the 20,000-dalton myosin light chains (LC 20) in rabbit tracheal smooth muscle modulates cross-bridge kinetics and isotonic shortening velocity. The thin muscle [190 +/- 10 (SE) microns] allowed detection of rapid changes in carbachol-induced active stress development, LC 20 phosphorylation, and isotonic shortening velocities. Phosphorylation of the LC 20 in resting muscle was 0.12 +/- 0.04 mol Pi/mol LC 20. Carbachol (10(-5) M) increased the level of phosphorylation to 0.46 +/- 0.03 mol Pi/mol LC 20 within 30 s. Phosphorylation then declined significantly as steady-state active stress was reached. A positive correlation was always found between LC 20 phosphorylation and shortening velocity. This result supports the hypothesis that the level of myosin phosphorylation was related to the mean cross-bridge cycling rate rather than the number of cross bridges contributing to the developed stress. Dephosphorylation of LC 20 occurred at about the same rate as the decline in shortening velocity and stress upon stimulus washout.

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.

Rate of heat production related to degree of filament overlap in chick ALD muscle

1977 ◽  
Vol 233 (1) ◽  
pp. C1-C7 ◽  
Author(s):  
Y. Matsumoto ◽  
A. M. McPhedran
Keyword(s):  
Heat Production ◽  
Length Change ◽  
Heat Liberation ◽  
Heavy Meromyosin ◽  
Thin Filaments ◽  
Cross Bridge ◽  
Single Cross ◽  
Anterior Latissimus Dorsi ◽  
Cross Bridges ◽  
Degree Of Overlap

The anterior latissimus dorsi (ALD) of chicks (2 wk old) was examined for rate of heat liberation when the muscle was reversibly stretched from L0 to about 1.6 L0. The "plateau" forces of isometric tetani were related to the corresponding rates of heat liberation. Presumably, in this region of length change the degree of overlap between the thick and thin filaments is changing. If the amount of overlap is known, the number of heavy meromyosin cross bridges in activity can be estimated. From this information, the amount of liberated energy can be calculated for a single cross-bridge cycling. In all of our measurements, there was heat production even at muscle lengths so great that no filament overlap would have to be assumed. This finding was incorported into the estimate for energy release per cross-bridge cycling.

Energy expenditure of longitudinal smooth muscle of rabbit urinary bladder

1987 ◽  
Vol 252 (1) ◽  
pp. C88-C96 ◽  
Author(s):  
I. R. Wendt ◽  
C. L. Gibbs
Keyword(s):  
Oxygen Consumption ◽  
Energy Expenditure ◽  
Total Energy ◽  
Heat Production ◽  
Lactate Production ◽  
Time Integral ◽  
Force Maintenance ◽  
Force Time ◽  
Rabbit Urinary Bladder ◽  
Force Time Integral

Heat production, oxygen consumption, and lactate production of longitudinal smooth muscle from rabbit urinary bladder has been measured at 27 degrees C. In isometric contractions (initiated by 1-Hz electrical stimulation) ranging in duration from 2 to 300 s, total energy expenditure correlated linearly with the force-time integral. For any given force-time integral oxygen consumption could account for only approximately 60% of the total energy measured as heat production. A substantial contribution of aerobic lactate production to the total energy flux was observed. This lactate production was also linearly correlated with force-time integral and was of sufficient magnitude to account for the discrepancy between total energy expenditure determined as heat production and oxygen consumption. The suprabasal rate of energy expenditure during the maintenance of force was approximately 2.6 mW/g and remained constant throughout contractions of up to 5-min duration, suggesting that in this muscle there is no change in the energetic cost of force maintenance with increasing duration of contraction. The rate of energy expenditure during the initial period of force development was, however, about twofold greater than that during subsequent force maintenance, indicating that there is an extra energy cost associated with the activation of contraction and development of force above that required for force maintenance.

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