Maximum speed of shortening and ATPase activity in atrial and ventricular myocardia of hyperthyroid rats

1995 ◽  
Vol 269 (3) ◽  
pp. C785-C790 ◽  
Author(s):  
R. Bottinelli ◽  
M. Canepari ◽  
V. Cappelli ◽  
C. Reggiani
Keyword(s):  
Atpase Activity ◽  
Ventricular Myocardium ◽  
Test Method ◽  
Maximum Speed ◽  
Kinetic Properties ◽  
Shortening Velocity ◽  
Myosin Heavy Chain Isoform ◽  
Force Velocity ◽  
The Difference ◽  
Speed Of Shortening

The kinetic properties of the myofibrillar system of atrial and ventricular myocardia of hyperthyroid rats were analyzed by determining ATPase activity and maximum shortening velocity. Hyperthyroidism was induced by daily subcutaneous injections of triiodothyronine (0.2 mg/kg body wt) for 2 wk. The treatment induced a marked atrial and ventricular hypertrophy and, in ventricular myocardium, an isomyosin shift toward a homogeneous V1 composition. Skinned trabeculae and purified myofibrils were prepared from atrial and ventricular myocardia. Enzymatic assays on the myofibrils showed that both Ca-stimulated ATPase activity and Ca-Mg-dependent ATPase activity had equal values in atrial and ventricular myocardia. In skinned trabeculae during maximal Ca activations, force-velocity curves were determined by load-clamp maneuvers, and unloaded shortening velocity (Vo) was obtained with the slack-test method. Both maximum shortening velocities extrapolated from the force-velocity curves (Vmax) and Vo were significantly higher (+68 and +52%, respectively) in atrial than in ventricular preparations. Developed tension was significantly greater in ventricular preparations. Maximum power output was not significantly different. Previous findings (V. Cappelli, R. Bottinelli, C. Poggesi, R. Moggio, and C. Reggiani. Circ. Res. 65: 446-457, 1989) had led to the conclusion that variations in ATPase activity and shortening velocity of ventricular myocardium can be accounted for by changes in isomyosin composition. In this light, the present results suggest that 1) ATPase activity is equal in atrial and ventricular myocardia as the two tissues contain the same myosin heavy chain isoform, 2) the difference in maximum speed of shortening between atrium and ventricle might be due to the presence of tissue-specific isoforms of myosin light chains.

Instantaneous force-velocity-length relations in isolated dog heart

1977 ◽  
Vol 232 (3) ◽  
pp. H241-H249 ◽  
Author(s):  
K. T. Weber ◽  
J. S. Janicki
Keyword(s):  
Fiber Length ◽  
Initial Period ◽  
Ventricular Myocardium ◽  
Left Ventricular ◽  
Steady State Response ◽  
Shortening Velocity ◽  
Contractile State ◽  
State Response ◽  
Force Velocity ◽  
Isolated Dog Heart

The mechanics of left ventricular contraction were investigated in terms of instantaneous mural force, mid-wall circumferential fiber shortening velocity (dL/dt), and fiber length (L) in seven servo-regulated hearts. The steady-state response of series of variably preloaded or afterloaded allasotonic contractions were utilized. Norepinephrine (0.55-1.38 mug/min) or propranolol (0.07-0.14 mg/min) were given to alter inotropic background. For any given contractile state and initial L, maximum dL/dt was not attained instantly but after a finite time of ejection (39 ms +/- 0.2 SE; range, 24-60) and from a lesser length (92% +/- 0.5 SE; range, 83-99) than present at end diastole. Beyond this initial period instantaneous dL/dt was dependent on both instantaneous force and length while independent of time after contraction and initial L. Instantaneous dL/dt also varied with contractile state, e.g., dL/dt was less after propranolol and greater after norepinephrine. Peak dL/dt for all conditions was a function of the extent of shortening (r = 0.90). Thus, the trajectory describing instantaneous force, velocity, and length provides a useful description of both the mechanical behavior and contractile state of the ventricular myocardium.

scholarly journals Differences in temperature dependence of muscle contractile properties and myofibrillar ATPase activity in a cold-temperature fish

1984 ◽  
Vol 111 (1) ◽  
pp. 179-189 ◽  
Author(s):  
I. A. Johnston ◽  
B. D. Sidell
Keyword(s):  
Atpase Activity ◽  
Test Method ◽  
Muscle Fibres ◽  
Contraction Velocity ◽  
Mechanical Constraints ◽  
Force Velocity ◽  
Skinned Fibre ◽  
Myoxocephalus Scorpius ◽  
Two Parameters ◽  
Triton X

Single muscle fibres were isolated from the fast myotomal muscle of the teleost Myoxocephalus scorpius L. and chemically skinned with 1% Brij. Maximum Ca2+-activated force (P0) increased from 14.5 +/− 1.1 N cm-2 at 2 degrees C to 19.1 +/− 1.8 N cm-2 at 15 degrees C (mean +/− S.E.). Maximum contraction velocity was determined by Hill's slack-test method (V0) and by extrapolation from force-velocity (P-V) relationships (Vmax). There was a linear relation between log10 V0 and temperature below 15 degrees C (Q10 = 1.9, P less than 0.01). The force-velocity characteristics of the fibres were determined at 2 degrees C and 20 degrees C. Points below 0.6 P0 on the P-V curve could be fitted by a linear form of Hill's equation. Extrapolated Vmax values were 0.55 muscle lengths s-1 (L0 s-1) at 2 degrees C and 1.54 L0 s-1 at 20 degrees C. Curvature of the P-V relationship was independent of temperature. The Mg2+, Ca2+-ATPase activity of Triton-X 100 extracted myofibrils was determined under similar ionic conditions to those used in skinned fibre experiments. (Ionic strength 0.16 mmol l-1, pMgATP 2.5). A linear relationship between log10 ATPase and temperature was only obtained below 15 degrees C (P less than 0.001). Above 15 degrees C, the Q10 for ATPase decreased significantly. The Q10(0–15 degrees C) for ATPase activity (3.9) was significantly higher than for unloaded contraction velocity. Supercontraction of isolated myofibrils to very short sarcomere lengths and differences in the mechanical constraints for crossbridge cycling between the preparations probably account for the lack of proportionality between these two parameters.

Force-velocity properties of fatigue-resistant units in cat fast-twitch muscle after fatigue

1987 ◽  
Vol 63 (4) ◽  
pp. 1511-1518 ◽  
Author(s):  
D. D. Hatcher ◽  
A. R. Luff
Keyword(s):  
Recovery Period ◽  
Motor Units ◽  
Isometric Tension ◽  
Maximum Speed ◽  
Control Value ◽  
Force Velocity ◽  
Flexor Digitorum ◽  
Fast Twitch ◽  
Whole Muscle ◽  
Speed Of Shortening

The isometric and force-velocity properties of an identified and uniform population of fast-twitch, fatigue-resistant (FR) fibers within the flexor digitorum longus (FDL) muscle were investigated before, immediately after, and during recovery from a fatiguing repetitive isometric stimulus regime (40 Hz for 330 ms every s for 180 s) in the anesthetized cat. It was necessary to determine the smallest fraction of muscle that had the same force-velocity properties as the whole muscle. This was approximately 15% for FDL; if the fraction was less, the maximum speed of shortening was depressed and the a/Po value increased. Motor units were enlarged by partial denervation of the muscle, causing the intact motoneurons to sprout and incorporate more muscle fibers; FR units showed the greatest increase. Immediately after the fatigue regime, maximum isometric tetanic tension declined to 67% but subsequently recovered to 90% of the control value by the end of the 60-min recovery period. Maximum speed of shortening dropped to 71% of the control but after 30 min had recovered and did not differ significantly from control values. It is concluded that the capacity for recovery from fatigue is greater for FR units than for a whole muscle, which also contains fast-fatiguable units, and that the mechanisms involved in the recovery of the maximum isometric tension and maximum speed of shortening are independently regulated.

Contractile properties of cat skeletal muscle after repetitive stimulation

1988 ◽  
Vol 64 (2) ◽  
pp. 502-510 ◽  
Author(s):  
D. D. Hatcher ◽  
A. R. Luff
Keyword(s):  
Recovery Period ◽  
Isometric Tension ◽  
Maximum Speed ◽  
Time To Peak ◽  
Force Velocity ◽  
Cross Bridges ◽  
Isometric Twitch ◽  
Flexor Digitorum ◽  
Fast Twitch ◽  
Speed Of Shortening

The isometric and force-velocity properties of the fast-twitch flexor digitorum longus (FDL) and slow-twitch soleus muscles were investigated immediately after and during recovery from a fatiguing stimulus regime (40 Hz for 330 ms every second for 180 s) in the anesthetized cat. The amplitude of the isometric twitch of FDL was unaffected but in soleus it remained depressed for much of the recovery period. Immediately after stimulation the twitch time to peak of FDL increased to 140% of the control (prefatigue) value and then reverted to control values. The maximum isometric tetanic tension (Po) developed by FDL was reduced to 67% of control values immediately after the stimulus regime, whereas soleus declined to 93% of control. Recovery of maximum force development was achieved after 45 min in FDL and after 15 min in soleus. The maximum speed of shortening of FDL was reduced to 63% of control values immediately after fatigue; despite some recovery within the first 30 min, it remained depressed during the remainder of the recovery period (up to 300 min). Maximum speed of shortening was unaltered in soleus. The a/Po value transiently increased to 176% of control values in FDL immediately after the fatigue regime but promptly returned to control values. Force-velocity properties of soleus were not affected by the stimulus regime. It is concluded that in FDL changes in the maximum speed of shortening and maximum isometric tension as a result of the stimulus regime are attributable to changes in the intrinsic behavior of cross-bridges and the metabolic status of the fibers, particularly in the fast-twitch fatigue-resistant fibers.

Isometric and isovelocity contractile performance of red musle fibres from the dogfishScyliorhinus canicula

2002 ◽  
Vol 205 (11) ◽  
pp. 1585-1595 ◽  
Author(s):  
F. Lou ◽  
N. A. Curtin ◽  
R. C. Woledge
Keyword(s):  
Isometric Force ◽  
Maximum Velocity ◽  
Test Method ◽  
Muscle Fibres ◽  
Shortening Velocity ◽  
Fibre Bundles ◽  
Series Elasticity ◽  
In Series ◽  
Force Velocity ◽  
Maximum Isometric Force

SUMMARYMaximum isometric tetanic force produced by bundles of red muscle fibres from dogfish, Scyliorhinus canicula (L.), was 142.4±10.3 kN m-2 (N=35 fibre bundles); this was significantly less than that produced by white fibres 289.2±8.4 kN m-2(N=25 fibre bundles) (means ± S.E.M.). Part, but not all, of the difference is due to mitochondrial content. The maximum unloaded shortening velocity, 1.693±0.108 L0 s-1(N=6 fibre bundles), was measured by the slack-test method. L0 is the length giving maximum isometric force. The force/velocity relationship was investigated using a step-and-ramp protocol in seven red fibre bundles. The following equation was fitted to the data:[(P/P0)+(a/P0)](V+b)=[(P0*/P0)+(a/P0)]b,where P is force during shortening at velocity V,P0 is the isometric force before shortening, and a, band P0* are fitted constants. The fitted values were P0*/P0=1.228±0.053, Vmax=1.814±0.071 L0s-1, a/P0=0.269±0.024 and b=0.404±0.041 L0 s-1(N=7 for all values). The maximum power was 0.107±0.005P0Vmax and was produced during shortening at 0.297±0.012Vmax. Compared with white fibres from dogfish, the red fibres have a lower P0 (49%) and Vmax (48%), but the shapes of the force/velocity curves are similar. Thus, the white and red fibres have equal capacities to produce power within the limits set by the isometric force and maximum velocity of shortening of each fibre type. A step shortening of 0.050±0.003L0 (N=7) reduced the maximum isometric force in the red fibres' series elasticity to zero. The series elasticity includes all elastic structures acting in series with the attached cross-bridges. Three red fibre bundles were stretched at a constant velocity, and force (measured when length reached L0) was 1.519±0.032P0. In the range of velocities used here, -0.28 to -0.63Vmax, force varied little with the velocity.

Transient length-related mechanical states in smooth muscle

1994 ◽  
Vol 72 (11) ◽  
pp. 1325-1333 ◽  
Author(s):  
Richard A. Meiss
Keyword(s):  
Mechanical Properties ◽  
Mathematical Model ◽  
Smooth Muscle ◽  
Internal Resistance ◽  
Steady Increase ◽  
Kinetic Properties ◽  
Shortening Velocity ◽  
Force Velocity ◽  
Isotonic Contractions ◽  
Isotonic Shortening

The isotonic shortening of electrically stimulated ovarian ligament smooth muscle strips from rabbits was studied by briefly applying sudden increases in afterload (force steps, 0.6 to 3.0 s long) just sufficient to halt the shortening. Upon removal of the extra afterload, the isotonic shortening velocity significantly increased compared with prestep velocities measured at the same muscle lengths. The degree of potentiation depended upon the duration of the force step. Muscles yielded initially when the step was applied, and their stiffness decreased. During the zero-velocity portion of the force step there was a steady increase in stiffness back to levels appropriate to that force. Complete force–velocity curves were made following short (0.6 s) and long (3.0 s) force steps. The values for Vmax (and all intermediate velocities) were significantly greater following a long force step. In a final experimental series, muscles were held isometric immediately after removal of the force step. Force rose monotonically, with a more rapid redevelopment following a long force step. A mathematical model is presented, according to which the effect of the duration of the force step on the poststep mechanical properties may be due to either the alteration of an internal resistance to shortening or a change in the kinetic properties of the cross-bridge array. A hypothesis is proposed relating the steady decline in isotonic shortening velocity to a partial local depletion of energy-yielding substrates.Key words: smooth muscle, isotonic contractions, mechanics, models.

Dependence of force, velocity, and O2 consumption on [Ca2+]o in porcine carotid artery

1988 ◽  
Vol 255 (3) ◽  
pp. C393-C400 ◽  
Author(s):  
J. M. Krisanda ◽  
R. J. Paul
Keyword(s):  
Steady State ◽  
Carotid Artery ◽  
Isometric Force ◽  
Test Method ◽  
O2 Consumption ◽  
Shortening Velocity ◽  
Tension Development ◽  
Calcium Dependent ◽  
The Difference ◽  
Porcine Carotid Artery

The relationship between extracellular calcium concentration ([Ca2+]o), isometric force (Fo), unloaded shortening velocity (Vus), and the rate of ATP utilization (JATP) were studied in vascular smooth muscle (VSM) during the steady state of an isometric contraction at 37 degrees C. Experiments were conducted on porcine carotid artery media strip and ring preparations that were stimulated with 109 mM KCl substituted for NaCl. Unloaded shortening velocity was estimated by the "slack" test method. Both Fo and Vus were dependent on [Ca2+]o. Vus at 7.5 mM [Ca2+]o was 1.7 times greater than Vus at 1.6 mM [Ca2+]o. The difference in force at these two Ca2+ concentrations was more variable than Vus, but in general was less than the change in Vus. The rate of ATP utilization was assessed from steady-state measurements of tissue O2 consumption. Increasing [Ca2+]o in the range of 0.15-7.5 mM resulted in an increase in both JATP and Fo. The relation between JATP and Fo was nonlinear with JATP increasing proportionately more than Fo between 1.6 and 7.5 mM Ca2+. The calcium-dependent increase in JATP appears to be primarily related to contractile protein interaction, since the effect of [Ca2+]o on JATP was substantially reduced during stimulation at short muscle lengths (Lmin), where tension development is absent. The economy of tension maintenance was 3.3. times greater when measured in the [Ca2+]o range of 0.15 and 1.6 mM than when measured at 1.6 to 7.5 mM [Ca2+]o. These data indicate that [Ca2+]o may regulate both the number and the rate of cycling of cross bridges in porcine carotid artery.

Maximum shortening speed of motor units of various types in cat lumbrical muscles

1993 ◽  
Vol 69 (2) ◽  
pp. 442-448 ◽  
Author(s):  
J. Petit ◽  
M. Chua ◽  
C. C. Hunt
Keyword(s):  
Motor Unit ◽  
Inverse Correlation ◽  
Motor Units ◽  
Maximum Speed ◽  
Single Motor Units ◽  
Maximal Speed ◽  
Contraction Times ◽  
Isometric Twitch ◽  
Lumbrical Muscles ◽  
Speed Of Shortening

1. Isotonic shortening of cat superficial lumbrical muscles was studied during maximal tetanic contractions of single motor units of identified types. For each motor unit, the maximal speed of contraction, Vmax, was determined by extrapolating to zero the hyperbolic relation between applied tension and speed of shortening. 2. The maximal speeds of shortening of motor units formed a continuum with the highest velocities observed for the fast fatigable motor units and the lowest for the slow motor units. 3. On average, the maximum speed of shortening increased with the tetanic tension developed by the motor units. 4. In motor units with isometric twitch contraction times less than 35 ms, these times showed a significant inverse correlation with Vmax. Progressively longer contraction times were associated with rather small changes in Vmax. 5. The implications of these findings on the speed of muscle shortening during motor-unit recruitment are discussed.

Force-velocity and force-power properties of single muscle fibers from elite master runners and sedentary men

1996 ◽  
Vol 271 (2) ◽  
pp. C676-C683 ◽  
Author(s):  
J. J. Widrick ◽  
S. W. Trappe ◽  
D. L. Costill ◽  
R. H. Fitts
Keyword(s):  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Power Output ◽  
Peak Power ◽  
Isometric Force ◽  
Peak Force ◽  
Peak Power Output ◽  
Type I ◽  
Shortening Velocity ◽  
Force Velocity

Gastrocnemius muscle fiber bundles were obtained by needle biopsy from five middle-aged sedentary men (SED group) and six age-matched endurance-trained master runners (RUN group). A single chemically permeabilized fiber segment was mounted between a force transducer and a position motor, subjected to a series of isotonic contractions at maximal Ca2+ activation (15 degrees C), and subsequently run on a 5% polyacrylamide gel to determine myosin heavy chain composition. The Hill equation was fit to the data obtained for each individual fiber (r2 > or = 0.98). For the SED group, fiber force-velocity parameters varied (P < 0.05) with fiber myosin heavy chain expression as follows: peak force, no differences: peak tension (force/fiber cross-sectional area), type IIx > type IIa > type I; maximal shortening velocity (Vmax, defined as y-intercept of force-velocity relationship), type IIx = type IIa > type I; a/Pzero (where a is a constant with dimensions of force and Pzero is peak isometric force), type IIx > type IIa > type I. Consequently, type IIx fibers produced twice as much peak power as type IIa fibers, whereas type IIa fibers produced about five times more peak power than type I fibers. RUN type I and IIa fibers were smaller in diameter and produced less peak force than SED type I and IIa fibers. The absolute peak power output of RUN type I and IIa fibers was 13 and 27% less, respectively, than peak power of similarly typed SED fibers. However, type I and IIa Vmax and a/Pzero were not different between the SED and RUN groups, and RUN type I and IIa power deficits disappeared after power was normalized for differences in fiber diameter. Thus the reduced absolute peak power output of the type I and IIa fibers from the master runners was a result of the smaller diameter of these fibers and a corresponding reduction in their peak isometric force production. This impairment in absolute peak power production at the single fiber level may be in part responsible for the reduced in vivo power output previously observed for endurance-trained athletes.

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