scholarly journals Effect of an ADP analog on isometric force and ATPase activity of active muscle fibers

2003 ◽  
Vol 284 (4) ◽  
pp. C816-C825 ◽  
Author(s):  
Christina Karatzaferi ◽  
Kathryn H. Myburgh ◽  
Marc K. Chinn ◽  
Kathleen Franks-Skiba ◽  
Roger Cooke
Keyword(s):  
Creatine Kinase ◽  
Simple Model ◽  
Atpase Activity ◽  
Isometric Force ◽  
Psoas Muscle ◽  
Isometric Tension ◽  
Active Muscle ◽  
Absolute Value ◽  
Cross Bridge ◽  
Skinned Muscle

The role played by ADP in modulating cross-bridge function has been difficult to study, because it is hard to buffer ADP concentration in skinned muscle preparations. To solve this, we used an analog of ADP, spin-labeled ADP (SL-ADP). SL-ADP binds tightly to myosin but is a very poor substrate for creatine kinase or pyruvate kinase. Thus ATP can be regenerated, allowing well-defined concentrations of both ATP and SL-ADP. We measured isometric ATPase rate and isometric tension as a function of both [SL-ADP], 0.1–2 mM, and [ATP], 0.05–0.5 mM, in skinned rabbit psoas muscle, simulating fresh or fatigued states. Saturating levels of SL-ADP increased isometric tension (by P′), the absolute value of P′ being nearly constant, ∼0.04 N/mm2, in variable ATP levels, pH 7. Tension decreased (50–60%) at pH 6, but upon addition of SL-ADP, P′ was still ∼0.04 N/mm2. The ATPase was inhibited competitively by SL-ADP with an inhibition constant, K i, of ∼240 and 280 μM at pH 7 and 6, respectively. Isometric force and ATPase activity could both be fit by a simple model of cross-bridge kinetics.

Skeletal muscle force and actomyosin ATPase activity reduced by nitric oxide donor

1997 ◽  
Vol 83 (4) ◽  
pp. 1326-1332 ◽  
Author(s):  
William J. Perkins ◽  
Young-Soo Han ◽  
Gary C. Sieck
Keyword(s):  
Nitric Oxide ◽  
Mechanical Properties ◽  
Atpase Activity ◽  
Muscle Force ◽  
Isometric Force ◽  
Nitric Oxide Donor ◽  
No Donor ◽  
Single Fibers ◽  
Actomyosin Atpase ◽  
Cross Bridge

Perkins, William J., Young-Soo Han, and Gary C. Sieck.Skeletal muscle force and actomyosin ATPase activity reduced by nitric oxide donor. J. Appl. Physiol.83(4): 1326–1332, 1997.—Nitric oxide (NO) may exert direct effects on actin-myosin cross-bridge cycling by modulating critical thiols on the myosin head. In the present study, the effects of the NO donor sodium nitroprusside (SNP; 100 μM to 10 mM) on mechanical properties and actomyosin adenosinetriphosphatase (ATPase) activity of single permeabilized muscle fibers from the rabbit psoas muscle were determined. The effects of N-ethylmaleimide (NEM; 5–250 μM), a thiol-specific alkylating reagent, on mechanical properties of single fibers were also evaluated. Both NEM (≥25 μM) and SNP (≥1 mM) significantly inhibited isometric force and actomyosin ATPase activity. The unloaded shortening velocity of SNP-treated single fibers was decreased, but to a lesser extent, suggesting that SNP effects on isometric force and actomyosin ATPase were largely due to decreased cross-bridge recruitment. The calcium sensitivity of SNP-treated single fibers was also decreased. The effects of SNP, but not NEM, on force and actomyosin ATPase activity were reversed by treatment with 10 mMdl-dithiothreitol, a thiol-reducing agent. We conclude that the NO donor SNP inhibits contractile function caused by reversible oxidation of contractile protein thiols.

scholarly journals Mavacamten Decreases Maximal Force and Ca2+-sensitivity in the N47K-Myosin Regulatory Light Chain Mouse Model of Hypertrophic Cardiomyopathy

2020 ◽  
Author(s):  
Peter O Awinda ◽  
Marissa Watanabe ◽  
Yemeserach M. Bishaw ◽  
Anna M Huckabee ◽  
Keinan B Agonias ◽  
...  
Keyword(s):  
Heart Disease ◽  
Hypertrophic Cardiomyopathy ◽  
Light Chain ◽  
Isometric Force ◽  
Regulatory Light Chain ◽  
Isometric Tension ◽  
Myosin Regulatory Light Chain ◽  
Cardiac Myosin ◽  
Cross Bridge ◽  
Obstructive Hypertrophic Cardiomyopathy

Morbidity and mortality associated with heart disease is a growing threat to the global population and novel therapies are needed. Mavacamten (formerly called MYK-461) is a small molecule that binds to cardiac myosin and inhibits myosin ATPase. Mavacamten is currently in clinical trials for the treatment of obstructive hypertrophic cardiomyopathy (HCM), and it may provide benefits for treating other forms of heart disease. We investigated the effect of mavacamten on cardiac muscle contraction in two transgenic mouse lines expressing the human isoform of cardiac myosin regulatory light chain (RLC) in their hearts. Control mice expressed wild-type RLC (WT-RLC), and HCM mice expressed the N47K RLC mutation. In the absence of mavacamten, skinned papillary muscle strips from WT-RLC mice produced greater isometric force than strips from N47K mice. Adding 0.3 µM mavacamten decreased maximal isometric force and reduced Ca2+-sensitivity of contraction for both genotypes, but this reduction in pCa50 was nearly twice as large for WT-RLC vs. N47K. We also used stochastic length-perturbation analysis to characterize cross-bridge kinetics. The cross-bridge detachment rate was measured as a function of [MgATP] to determine the effect of mavacamten on myosin nucleotide handling rates. Mavacamten increased the MgADP release and MgATP binding rates for both genotypes, thereby contributing to faster cross-bridge detachment, which could speed myocardial relaxation during diastole. Our data suggest that mavacamten reduces isometric tension and Ca2+-sensitivity of contraction via decreased strong cross-bridge binding. Mavacamten may become a useful therapy for patients with heart disease, including some forms of HCM.

BDM affects nucleotide binding and force generation steps of the cross-bridge cycle in rabbit psoas muscle fibers

1994 ◽  
Vol 266 (2) ◽  
pp. C437-C447 ◽  
Author(s):  
Y. Zhao ◽  
M. Kawai
Keyword(s):  
Equilibrium Constants ◽  
Muscle Fibers ◽  
Psoas Muscle ◽  
Isometric Tension ◽  
Activation Mechanism ◽  
Phosphate Binding ◽  
Rabbit Psoas ◽  
Cross Bridge ◽  
The Cross ◽  
Cross Bridges

The effect of 2,3-butanedione monoxime (BDM) on elementary steps of the cross-bridge cycle was studied with the sinusoidal analysis technique in skinned rabbit psoas muscle fibers. Our results showed that isometric tension and stiffness decreased progressively with an increase in the BDM concentration. The MgATP and MgADP binding constants increased 27 and 6 times, respectively, when BDM was increased from 0 to 18 mM, whereas the phosphate binding constant did not change significantly. The equilibrium constants of the ATP isomerization and detachment step were not sensitive to BDM, whereas the equilibrium constant of the attachment (power stroke) step decreased with BDM. Thus, in the presence of BDM, the number of attached cross bridges decreases; more cross bridges accumulate in the detached state, causing isometric tension and stiffness to decline. However, our detailed analysis shows that the decrease in the number of attached cross bridges is approximately 40%, which is not adequate to account for the 84% decrease in the isometric tension when 18 mM BDM was present. Therefore we suggest that a thin-filament activation mechanism is also affected by BDM.

scholarly journals Mechanical Responses of a Crustacean Slow Muscle

1983 ◽  
Vol 107 (1) ◽  
pp. 367-383 ◽  
Author(s):  
WILLIAM D. CHAPPLE
Keyword(s):  
Short Range ◽  
Motor Nerve ◽  
Maximum Velocity ◽  
Isometric Tension ◽  
Muscle Stiffness ◽  
Gradual Transition ◽  
Active Muscle ◽  
Cross Bridge ◽  
Reference Length ◽  
Activation Level

1. Mechanical properties of the abdominal ventral superficial muscle of the hermit crab, Pagurus pollicarus, were examined under isometric and iso-velocity conditions. The muscle was activated by stimulating its motor nerve at different frequencies. 2. Length-isometric tension relations were measured. Peak tension, P0, was 0.16–0.2MNm−2 and the sarcomere length of the muscle at the optimum length, L0, was 10.8+1.0 μm. Passive tension was high at L0. Correlated measurements of the operating length of the muscle and L0 indicate that the operating length is at a point on the ascending limb of the length-tension curve approximately 0.77 L0. 3. The relationship between activation level of the muscle and the length-tension relation indicates that the curve is not substantially displaced along the length axis by increasing activation level; increased force is primarily due to an increase in the slope of the ascending limb of the curve. 4. The force-velocity relation was obtained by measuring the force at a reference length during iso-velocity shortening of an active muscle. Hill constants of a/P0 = 0.11 + 0.02 and b = 1.07 = 0.24 mm s−1 were obtained. The maximum velocity of shortening per half sarcomere was approximately 4.2μms−1. 5. Stretch of an active muscle did not produce an abrupt short range yield but a gradual transition between short range and terminal stiffness. This behaviour is shown to be due not to differences in cross bridge stiffness between VSM and other muscle but to a non cross bridge stiffness with a value that is one-fifth that of vertebrate muscle. 6. Such a low stiffness may provide an intrinsic mechanism for simplifying load compensation in the absence of rapid proprioceptive reflexes for the control of muscle stiffness.

Tension and ATPase rate in steady-state contractions of rabbit soleus fiber segments

1983 ◽  
Vol 245 (5) ◽  
pp. C405-C414 ◽  
Author(s):  
B. H. Krasner ◽  
M. J. Kushmerick
Keyword(s):  
Steady State ◽  
Atpase Activity ◽  
Calcium Ion ◽  
Isometric Tension ◽  
Ion Concentration ◽  
Cross Bridge ◽  
A Value ◽  
Tension Time ◽  
Calcium Ion Concentration ◽  
Substrate Concentrations

Steady-state isometric tension and ATPase were studied in hyperpermeable segments of single muscle fibers from rabbit soleus muscle at 22 degrees C. The ATPase activity was due to actomyosin. The ratio of fiber ATPase to tension was used as an index of steady-state cross-bridge kinetics. Increasing the calcium ion concentration from pCa 8 to pCa 5 activated both tension and ATPase. The maximal tension was 1.35 +/- 0.07 kg/cm2. The maximal ATPase was 1.05 +/- 0.13 mumol X g-1. s-1 at pCa 5.2. ATPase activity increased with tension, such that the ratio of ATPase to tension remained constant at all calcium concentrations. In the absence of calcium, increasing the concentration of MgATP from 1 to 7 X 10(-7) M increased tension from zero to a maximum of 0.46 +/- 0.03 kg/cm2. Increasing MgATP concentration further to 1 X 10(-6) M inhibited tension. In the phase of rising tension, ATPase increased proportionally to tension, to 0.11 +/- 0.01 mumol X g-1 X s-1 at maximum tension. However, the ratio of ATPase to tension on the rising phase had a value only one-third of that seen with calcium-activated tension. Thus, low substrate concentrations, but not low calcium ion concentrations, influence cross-bridge kinetics under steady-state isometric conditions, possibly by an increase in the tension-time product during a cross-bridge cycle.

scholarly journals Variations in cross-bridge attachment rate and tension with phosphorylation of myosin in mammalian skinned skeletal muscle fibers. Implications for twitch potentiation in intact muscle.

1989 ◽  
Vol 93 (5) ◽  
pp. 855-883 ◽  
Author(s):  
J M Metzger ◽  
M L Greaser ◽  
R L Moss
Keyword(s):  
Steady State ◽  
Light Chain ◽  
Time Course ◽  
Myosin Light Chain ◽  
Isometric Force ◽  
Vastus Lateralis ◽  
Isometric Tension ◽  
National Academy Of Sciences ◽  
Cross Bridge ◽  
Myosin Light Chain 2

The Ca2+ sensitivities of the rate constant of tension redevelopment (ktr; Brenner, B., and E. Eisenberg. 1986. Proceedings of the National Academy of Sciences. 83:3542-3546) and isometric force during steady-state activation were examined as functions of myosin light chain 2 (LC2) phosphorylation in skinned single fibers from rabbit and rat fast-twitch skeletal muscles. To measure ktr the fiber was activated with Ca2+ and steady isometric tension was allowed to develop; subsequently, the fiber was rapidly (less than 1 ms) released to a shorter length and then reextended by approximately 200 nm per half sarcomere. This maneuver resulted in the complete dissociation of cross-bridges from actin, so that the subsequent redevelopment of tension was related to the rate of cross-bridge reattachment. The time course of tension redevelopment, which was recorded under sarcomere length control, was best fit by a first-order exponential equation (i.e., tension = C(1 - e-kt) to obtain the value of ktr. In control fibers, ktr increased sigmoidally with increases in [Ca2+]; maximum values of ktr were obtained at pCa 4.5 and were significantly greater in rat superficial vastus lateralis fibers (26.1 +/- 1.2 s-1 at 15 degrees C) than in rabbit psoas fibers (18.7 +/- 1.0 s-1). Phosphorylation of LC2 was accomplished by repeated Ca2+ activations (pCa 4.5) of the fibers in solutions containing 6 microM calmodulin and 0.5 microM myosin light chain kinase, a protocol that resulted in an increase in LC2 phosphorylation from approximately 10% in the control fibers to greater than 80% after treatment. After phosphorylation, ktr was unchanged at maximum or very low levels of Ca2+ activation. However, at intermediate levels of Ca2+ activation, between pCa 5.5 and 6.2, there was a significant increase in ktr such that this portion of the ktr-pCa relationship was shifted to the left. The steady-state isometric tension-pCa relationship, which in control fibers was left shifted with respect to the ktr-pCa relationship, was further left-shifted after LC2 phosphorylation. Phosphorylation of LC2 had no effect upon steady-state tension during maximum Ca2+ activation. In fibers from which troponin C was partially extracted to disrupt molecular cooperativity within the thin filament (Moss et al. 1985. Journal of General Physiology. 86:585-600), the effect of LC2 phosphorylation to increase the Ca2+ sensitivity of steady-state isometric force was no longer evident, although the effect of phosphorylation to increase ktr was unaffected by this maneuver.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals The Transient Mechanics of Muscle Require Only a Single Force-Producing Cross-Bridge State and a 100 Å Working Stroke

Biology ◽  
2020 ◽  
Vol 9 (12) ◽  
pp. 475
Author(s):  
Carlo Knupp ◽  
John M. Squire
Keyword(s):  
Simple Model ◽  
The Other ◽  
Active Muscle ◽  
Step Size ◽  
Constant Length ◽  
X Ray ◽  
Cross Bridge ◽  
Mechanical Explanation ◽  
Single Force ◽  
Cross Bridges

An informative probe of myosin cross-bridge behaviour in active muscle is a mechanical transient experiment where, for example, a fully active muscle initially held at constant length is suddenly shortened to a new fixed length, providing a force transient, or has its load suddenly reduced, providing a length transient. We describe the simplest cross-bridge mechanical cycle we could find to model these transients. We show using the statistical mechanics of 50,000 cross-bridges that a simple cycle with two actin-attached cross-bridge states, one producing no force and the other producing force, will explain much of what has been observed experimentally, and we discuss the implications of this modelling for our understanding of how muscle works. We show that this same simple model will explain, reasonably well, the isotonic mechanical and X-ray transients under different loads observed by Reconditi et al. (2004, Nature 428, 578) and that there is no need to invoke different cross-bridge step sizes under these different conditions; a step size of 100 Å works well for all loads. We do not claim that this model provides a total mechanical explanation of how muscle works. However, we do suggest that only if there are other observations that cannot be explained by this simple model should something more complicated be considered.

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.

Caffeine alters cardiac myofilament activity and regulation independently of Ca2+ binding to troponin C

1995 ◽  
Vol 268 (6) ◽  
pp. C1348-C1353 ◽  
Author(s):  
F. M. Powers ◽  
R. J. Solaro
Keyword(s):  
Atpase Activity ◽  
Isometric Force ◽  
Troponin C ◽  
Fiber Bundles ◽  
Direct Effects ◽  
Skinned Fiber ◽  
Myofilament Function ◽  
Cardiac Myofilament ◽  
Myosin Interaction ◽  
Skinned Fiber Bundles

We investigated the mechanism by which caffeine influences myofilament responsiveness to Ca2+ by measuring isometric force, Ca2+ binding, and ATPase activity of dog cardiac myofilament proteins. Caffeine (20 mM) increased submaximal and depressed maximal force in skinned fiber bundles. Although the Ca2+ sensitivity of myofilament activity was increased by caffeine, there was no effect on Ca2+ binding to troponin C (TnC) in skinned fiber bundles. To determine if caffeine altered actin-myosin interaction or affected myosin directly, myofibrillar, actomyosin, and myosin ATPase activities were measured. Maximal Ca(2+)-activated myofibrillar Mg(2+)-ATPase activity was depressed by 20 mM caffeine, whereas submaximal Mg(2+)-ATPase activities were not changed. Actomyosin Mg(2+)-ATPase activity was significantly depressed by caffeine concentrations > or = 15 mM. Myosin Ca(2+)-ATPase activity was depressed by caffeine, whereas Mg(2+)-ATPase and K(EDTA)-ATPase activities were not affected. These data suggest that caffeine affects myofilament function via a mechanism that is independent of TnC-Ca2+ binding but that may involve direct effects on actin-cross-bridge interaction.

Sign in / Sign up

Export Citation Format

Share Document