Force-interval relation in normal and cardiomyopathic hamster atria

1991 ◽  
Vol 261 (5) ◽  
pp. H1597-H1602
Author(s):  
S. E. Howlett ◽  
J. Bobet ◽  
T. Gordon
Keyword(s):  
Steady State ◽  
Isometric Force ◽  
Contractile Force ◽  
Single Test ◽  
Interval Relation ◽  
Intracellular Compartments ◽  
Short Test ◽  
State Force ◽  
Single Exponential

The purpose of this study was to determine how cardiomyopathy affects the beat-to-beat regulation of contractile force in cardiac muscle. Isometric force produced by left atria from 80- to 85-day-old normal and cardiomyopathic (CM) hamsters was measured in vitro at 29 degrees C in 2.5 and 6.0 mM Ca2+. During steady-state stimulation at 1 Hz, single test stimuli were interpolated at varying test intervals (0.3-600 s). The force-interval curves were fitted with an equation using five parameters to define the curve and were compared under different conditions; the recovery of force after long rest intervals was fitted with a single exponential curve. Results showed that the force-interval curves were similar in normal and CM atria except that force was depressed at all intervals in 2.5 mM external Ca2+ concentration ([Ca2+]e) and that the parameter U(0), reflecting force produced at short test intervals, tended to be lower in CM muscles. At high [Ca2+]e (6.0 mM) the force-interval curves were similar, but recovery of steady-state force after long test intervals was much slower in CM atria (tau = 77.3 +/- 8.5 s, n = 11) than in normal atria (tau = 30.5 +/- 3.9 s, n = 11). Recovery was also slower at 2.5 mM [Ca2+]e. These findings suggest that, on a beat-to-beat basis, there is less Ca2+ available in intracellular compartments in the CM heart.

scholarly journals Force enhancement after stretch of isolated myofibrils is increased by sarcomere length non-uniformities

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Ricarda M. Haeger ◽  
Dilson E. Rassier
Keyword(s):  
Steady State ◽  
Sarcomere Length ◽  
Isometric Force ◽  
Force Production ◽  
Force Enhancement ◽  
Residual Force ◽  
Residual Force Enhancement ◽  
State Force ◽  
Isometric Forces

AbstractWhen a muscle is stretched during a contraction, the resulting steady-state force is higher than the isometric force produced at a comparable sarcomere length. This phenomenon, also referred to as residual force enhancement, cannot be readily explained by the force-sarcomere length relation. One of the most accepted mechanisms for the residual force enhancement is the development of sarcomere length non-uniformities after an active stretch. The aim of this study was to directly investigate the effect of non-uniformities on the force-producing capabilities of isolated myofibrils after they are actively stretched. We evaluated the effect of depleting a single A-band on sarcomere length non-uniformity and residual force enhancement. We observed that sarcomere length non-uniformity was effectively increased following A-band depletion. Furthermore, isometric forces decreased, while the percent residual force enhancement increased compared to intact myofibrils (5% vs. 20%). We conclude that sarcomere length non-uniformities are partially responsible for the enhanced force production after stretch.

scholarly journals A new experimental model for force enhancement: steady-state and transient observations of the Drosophila jump muscle

2015 ◽  
Vol 309 (8) ◽  
pp. C551-C557 ◽  
Author(s):  
Ryan A. Koppes ◽  
Douglas M. Swank ◽  
David T. Corr
Keyword(s):  
Steady State ◽  
Experimental Model ◽  
Isometric Force ◽  
Underlying Mechanism ◽  
Passive Component ◽  
Force Enhancement ◽  
Force Relaxation ◽  
Two Phases ◽  
State Force ◽  
Structural Levels

The increase in steady-state force after active lengthening in skeletal muscle, termed force enhancement (FE), has been observed for nearly one century. Although demonstrated experimentally at various structural levels, the underlying mechanism(s) remain unknown. We recently showed that the Drosophila jump muscle is an ideal model for investigating mechanisms behind muscle physiological properties, because its mechanical characteristics, tested thus far, duplicate those of fast mammalian skeletal muscles, and Drosophila has the advantage that it can be more easily genetically modified. To determine if Drosophila would be appropriate to investigate FE, we performed classic FE experiments on this muscle. Steady-state FE (FESS), following active lengthening, increased by 3, 7, and 12% of maximum isometric force, with increasing stretch amplitudes of 5, 10, and 20% of optimal fiber length (FLOPT), yet was similar for stretches across increasing stretch velocities of 4, 20, and 200% FLOPT/s. These FESS characteristics of the Drosophila jump muscle closely mimic those observed previously. Jump muscles also displayed typical transient FE characteristics. The transient force relaxation following active stretch was fit with a double exponential, yielding two phases of force relaxation: a fast initial relaxation of force, followed by a slower recovery toward steady state. Our analyses identified a negative correlation between the slow relaxation rate and FESS, indicating that there is likely an active component contributing to FE, in addition to a passive component. Herein, we have established the Drosophila jump muscle as a new and genetically powerful experimental model to investigate the underlying mechanism(s) of FE.

Myosin light chain phosphorylation associated with contraction in arterial smooth muscle

1981 ◽  
Vol 240 (5) ◽  
pp. C222-C233 ◽  
Author(s):  
S. P. Driska ◽  
M. O. Aksoy ◽  
R. A. Murphy
Keyword(s):  
Smooth Muscle ◽  
Steady State ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Isometric Force ◽  
Physiological Salt Solution ◽  
Physiological Control ◽  
The Media ◽  
Low Levels ◽  
State Force

The hypothesis that Ca2+ initiates contraction in smooth muscle by activating an endogenous myosin light chain kinase (MLCK) that phosphorylates the 20,000 dalton light chain (LC 20) of myosin was tested in tissues prepared from the media of swine carotid arteries. Unstimulated tissues with low levels of tone exhibited low levels of phosphorylated LC 20. On stimulation with a high-K+ physiological salt solution containing 1.6 mM CaCl2, LC 20 phosphorylation increased to 0.6 mol P/mol LC 20 within 30 s. This increase preceded force development, which required 2-4 min to attain a maximum steady-state value of 3.34 +/- 0.15 (SE) X 10(5) N/m2. These results support the hypothesis, as the stimulus was submaximal for the preparation. However, LC 20 phosphorylation declined significantly from its peak value before steady-state force was attained, reaching near control levels after 10 min of stimulation. The results suggest that Ca2+-stimulated LC 20 phosphorylation is an important physiological control mechanism but that additional factors are involved in the maintenance of tonic isometric force.

Transient and Steady-State Force Enhancement in the Drosophila Jump Muscle

2012 ◽  
Author(s):  
Ryan A. Koppes ◽  
Douglas M. Swank ◽  
David T. Corr
Keyword(s):  
Steady State ◽  
Isometric Force ◽  
Recovery Period ◽  
Underlying Mechanism ◽  
Clear Correlation ◽  
Force Enhancement ◽  
Force Depression ◽  
Force Recovery ◽  
State Force ◽  
Whole Muscle

The increase of isometric force after active lengthening, termed force enhancement (FE), is a well-accepted characteristic of skeletal muscle that has been demonstrated in both whole muscle [1,3] and single-fiber preparations [1,2]. The amount of FE increases with increasing amplitudes of stretch, yet no clear correlation between FE and the rate stretch has been demonstrated [2]. Although this behavior has been observed experimentally for over 70 years, its underlying mechanism(s) remain unknown. Furthermore, most studies of FE have been limited to steady-state (FESS) observations [1–3], whereas clues to the underlying mechanism(s) may very well exist in the transient force recovery period following an active stretch, as seen in another history-dependent phenomenon, force depression [4].

scholarly journals Gene transfer, expression, and sarcomeric incorporation of a headless myosin molecule in cardiac myocytes: evidence for a reserve in myofilament motor function

2011 ◽  
Vol 300 (2) ◽  
pp. H574-H582 ◽  
Author(s):  
Rene Vandenboom ◽  
Todd Herron ◽  
Elizabeth Favre ◽  
Faris P. Albayya ◽  
Joseph M. Metzger
Keyword(s):  
Steady State ◽  
Gene Transfer ◽  
Contractile Function ◽  
Isometric Force ◽  
Motor Domain ◽  
Confocal Imaging ◽  
Flag Epitope ◽  
Cardiac Sarcomere ◽  
Immunofluorescence Labeling

The purpose of this study was to implement a living myocyte in vitro model system to test whether a motor domain-deleted headless myosin construct could be incorporated into the sarcomere and affect contractility. To this end we used gene transfer to express a “headless” myosin heavy chain (headless-MHC) in complement with the native full-length myosin motors in the cardiac sarcomere. An NH2-terminal Flag epitope was used for unique detection of the motor domain-deleted headless-MHC. Total MHC content (i.e., headless-MHC + endogenous MHC) remained constant, while expression of the headless-MHC in transduced myocytes increased from 24 to 72 h after gene transfer until values leveled off at 96 h after gene transfer, at which time the headless-MHC comprised ∼20% of total MHC. Moreover, immunofluorescence labeling and confocal imaging confirmed expression and demonstrated incorporation of the headless-MHC in the A band of the cardiac sarcomere. Functional measurements in intact myocytes showed that headless-MHC modestly reduced amplitude of dynamic twitch contractions compared with controls ( P < 0.05). In chemically permeabilized myocytes, maximum steady-state isometric force and the tension-pCa relationship were unaltered by the headless-MHC. These data suggest that headless-MHC can express to 20% of total myosin and incorporate into the sarcomere yet have modest to no effects on dynamic and steady-state contractile function. This would indicate a degree of functional tolerance in the sarcomere for nonfunctional myosin molecules.

Mysteries of Muscle Contraction

2008 ◽  
Vol 24 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Walter Herzog ◽  
Timothy R. Leonard ◽  
Venus Joumaa ◽  
Ashi Mehta
Keyword(s):  
Steady State ◽  
Experimental Evidence ◽  
Active Component ◽  
Isometric Force ◽  
Force Production ◽  
Myosin Filament ◽  
Passive Component ◽  
Cross Bridge ◽  
The Cross ◽  
State Force

According to the cross-bridge theory, the steady-state isometric force of a muscle is given by the amount of actin–myosin filament overlap. However, it has been known for more than half a century that steady-state forces depend crucially on contractile history. Here, we examine history-dependent steady-state force production in view of the cross-bridge theory, available experimental evidence, and existing explanations for this phenomenon. This is done on various structural levels, ranging from the intact muscle to the myofibrillar and isolated contractile protein level, so that advantages and limitations of the various preparations can be fully exploited and overcome. Based on experimental evidence, we conclude that steady-state force following active muscle stretching is enhanced, and this enhancement has a passive and an active component. The active component is associated with the cross-bridge kinetics, and the passive component is associated with a calcium-dependent increase in titin stiffness.

Analysis of Halothane Effects on Myocardial Force-Interval Relationships at Anesthetic Concentrations Depressing Twitches but Not Tetanic Contractions

1995 ◽  
Vol 83 (5) ◽  
pp. 1055-1064 ◽  
Author(s):  
Stephen M. Vogel ◽  
Guy L. Weinberg ◽  
Andreja Djokovic ◽  
David J. Miletich ◽  
Ronald F. Albrecht
Keyword(s):  
Mathematical Model ◽  
Sarcoplasmic Reticulum ◽  
Contractile Force ◽  
Rat Myocardium ◽  
Twitch Force ◽  
Differential Effects ◽  
Intracellular Compartments ◽  
In Vitro Effects

Abstract Background Tetanic contractions in rat myocardium depend solely on cellular Calcium2+ uptake, whereas twitches depend on Calcium2+ release from the sarcoplasmic reticulum. Because halothane may cause loss of sequestered Calcium2+, the anesthetic was tested for its differential effects on twitch and tetanic forces. The in vitro effects of halothane on the twitch force-interval relationship were then evaluated, using a mathematical model that relates twitch contractile force to the Calcium2+ content of intracellular compartments.

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