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PubMed1999

Attenuation of rat diaphragm low-frequency fatigue by vanadate in vitro.

Sodium vanadate inhibits protein tyrosine phosphatases, including in skeletal muscle. Vanadate increases contractile force of airway, vascular and gastrointestinal smooth muscle. The present study tested the hypothesis that vanadate augments skeletal muscle contractility. Rat diaphragm muscle strips (n=26 from 12 animals) were studied in vitro at 37 degrees C. Muscles contracted isometrically while stimulated supramaximally with one of two protocols: 30 min of continuous 0.1 Hz stimulation, or 5 min of intermittent 20 Hz stimulation (duty cycle 0.33). Vanadate (500 microM)-treated muscle strips were compared with untreated muscle. Vanadate did not affect force or isometric twitch kinetics of otherwise quiescent muscle. During prolonged 0.1 Hz stimulation, force of control muscles declined by 17 +/- 4% over 30 min, whereas muscles incubated with vanadate maintained force virtually unchanged. Force over time was significantly greater with than without vanadate (P = 0.03), with values being significantly different during the last 10 min of the 30 min stimulation period. In the absence of vanadate force declined at a rate of approximately 0.6% per min, whereas with vanadate the rate of force decline was less than 0.1% per min (P < 0.02). During intermittent 20 Hz stimulation, the degree of force decline was not affected by vanadate at any time over a course of 5 min. Isometric contractile kinetics were not altered by vanadate during either 0.1 or 20 Hz stimulation. These data suggest that vanadate ameliorates low- but not higher-frequency fatigue in diaphragm, suggesting a role for protein tyrosine phosphorylation in the regulation of muscle fatigue resistance.

Animals↗

PubMed1993

A structural and kinetic study on myofibrils prevented from shortening by chemical cross-linking.

In previous work, we studied the early steps of the Mg(2+)-ATPase activity of Ca(2+)-activated myofibrils [Houadjeto, M., Travers, F., & Barman, T. (1992) Biochemistry 31, 1564-1569]. The myofibrils were free to contract, and the results obtained refer to the ATPase cycle of myofibrils contracting with no external load. Here we studied the ATPase of myofibrils contracting isometrically. To prevent shortening, we cross-linked them with 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC). SDS-PAGE and Western blot analyses showed that the myosin rods were extensively cross-linked and that 8% of the myosin heads were cross-linked to the thin filament. The transient kinetics of the cross-linked myofibrils were studied in 0.1 M potassium acetate, pH 7.4 and 4 degrees C, by the rapid-flow quench method. The ATP binding steps were studied by the cold ATP chase and the cleavage and release of products steps by the Pi burst method. In Pi burst experiments, the sizes of the bursts were equal within experimental error to the ATPase site concentrations (as determined by the cold ATP chase methods) for both cross-linked (isometric) and un-cross-linked (isotonic) myofibrils. This shows that in both cases the rate-limiting step is after the cleavage of ATP. When cross-linked, the kcat of Ca(2+)-activated myofibrils was reduced from 1.7 to 0.8 s-1. This is consistent with the observation that fibers shortening at moderate velocity have a higher ATPase activity than isometric fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗

PubMed2003

Why choose myofibrils to study muscle myosin ATPase?

Our objective is to propose an overview of the usefulness of skeletal myofibril as an experimental system for studying mechanochemical coupling of skeletal muscles and myosin ATPase activity. The myofibril is a true functional mini-muscle that is able to contract in the presence of ATP. It also contains the machinery necessary for the calcium sensitivity of the contraction. In the absence of calcium, myofibrillar ATPase activity is basal, no shortening occurs and no active force is developed. In the presence of calcium, myofibrillar ATPase is activated and myofibrils either shorten with no external load (native myofibrils) or contract isometrically (cross-linked myofibrils). With this organised system, both chemical and mechanical studies can be carried out. For a decade, our laboratory has been using rabbit psoas myofibrils for exploring myosin ATPase activity. The first challenge was to successfully apply rapid kinetic approaches, such as rapid-flow-quench, to this organised system. Another challenge was to work with myofibrils in cryoenzymic conditions, i.e. in the presence of organic solvents and at sub-zero temperatures. In this overview, we highlight differences between the myosin ATPase in organised systems (myofibrils or fibres) and that of contractile proteins in solution (S1 or actoS1) that we observed using these approaches. We discuss the importance of these differences in terms of mechanochemical coupling. It is concluded that great care should be taken when extrapolating mechanochemical properties of the contractile proteins in solution to the whole muscle.

Actins↗

PubMed1990

Surgical repair of ruptured Achilles tendon in sportsmen and sedentary patients: a longitudinal ultrasound assessment.

Ultrasound scanning was performed at different postoperative times on a total of 22 patients who underwent an end-to-end suture using absorbable material following a full thickness subcutaneous rupture of their Achilles tendon. All ultrasonic examinations were performed using a 5 MHz sectorial probe. The parameters taken into account were the size of the tendon, its borders and echographic pattern, the possible surgical sequelae, and residual pathology. Moreover, maximal isometric voluntary contraction, isometric endurance, and toe raising were tested. The patients' personal postoperative condition and satisfaction was also assessed. The operated tendon remained of increased thickness 9 months after surgery, and the suture material, although absorbable, was still visible on ultrasound scans at that time. Diagnostic ultrasonography can be used as a guide for physiotherapy in patients undergoing surgery for rupture of the Achilles tendon.

Achilles Tendon↗

PubMedDate not supplied

Effects of CM7857, a derivative of disopyramide, on electrophysiologic properties of canine Purkinje fibers and inotropic properties of canine ventricular muscle.

Effects of CM7857 on electrophysiologic properties in canine Purkinje fibers and inotropic effects in canine ventricular muscle were studied. As CM7857 is a derivative of disopyramide phosphate, the effects of CM7857 (5 mg/L, 1.5 X 10(-5) M) were compared with those of disopyramide phosphate (5 mg/L, 1.4 X 10(-5) M). CM7857 significantly lowered the maximum rate of rise of phase 0 (Vmax) from 351.5 +/- 50.6 V/s (mean +/- SE, n = 5) to 283.6 +/- 33.0 V/s, and conduction velocity from 2.68 +/- 0.56 m/s to 1.70 +/- 0.28 m/s. The automaticity of Purkinje fibers was depressed by CM7857 as the result of reduction in the slope of phase 4. These effects were comparable to those of disopyramide. A marked difference between CM7857 and disopyramide was observed in the effect on action potential duration. APD90 was significantly shortened from 327.4 +/- 14.8 ms (n = 8) to 279.9 +/- 12.9 ms by CM7857, whereas disopyramide did not show any significant changes in APD90. As the CM7857-induced shortening of APD disappeared in low [Na+]o or low [K+]o concentration, it may be attributed to the lowering effect of "window current," a steady-state sodium current, maintaining action potential plateau. Effective refractory period (ERP) did not show any significant change. An acetylstrophanthidin-induced oscillatory afterpotential was significantly depressed by disopyramide, but not by CM7857. Isotonic contraction and isometric contraction of the right ventricular trabecullae were depressed by both drugs.

Action Potentials↗

PubMed1991

Alternative parameters for evaluating the performance of skeletal muscle in cardiac assistance.

This article describes a system designed to study the force, intramuscular pressure (IP), thickening (TH), and electromyographic (EMG) activity of the latissimus dorsi muscle in response to electrical stimulation. Experiments were carried out on fresh unconditioned muscles freed from the left flank insertion and fixed to contract isometrically. Statistical analysis of the data obtained demonstrated that IP and EMG activity were linearly related to force. The thickening of the muscle was found to be sensitive only to large variations in force, in a linear fashion.

Animals↗

PubMed1986

Observations on the automatic compensation of reflex gain on varying the pre-existing level of motor discharge in man.

The human stretch reflex is well known to show 'automatic gain compensation'; in other words, the electromyographic (e.m.g.) response evoked by a given disturbance increases progressively with the level of pre-existing voluntary activity, and so remains an approximately constant proportion of the background. Such behaviour has now been observed using vibration as the stimulus to Ia action and recording the reflexly developed force, in addition to the e.m.g. Inhibition was studied as well as excitation by vibrating the antagonist as well as the agonist, and found to be similarly regulated. The experiments were performed on the elbow flexors while they were contracting isometrically under voluntary drive. The vibration was either square-wave modulated at 5 Hz or delivered in bursts of one to five pulses. The latency of the e.m.g. responses produced by the latter was sufficiently short to show that gain compensation was a feature of spinal reflex action. In the Discussion, it is concluded that in principle 'automatic gain compensation' can be readily attributed to the known organization of the motoneurone pool. As the background force increases so does the number of active motoneurones available to be frequency-modulated by a given input, and the larger and stronger will be those motor units which are on the verge of recruitment or de-recruitment.

Adult↗

PubMed1988

Stretch sensitization of human muscle spindles.

1. Sixty-seven afferents from the finger extensor muscles were consecutively recorded by microneurography. 2. The units were classified as primary or secondary muscle spindle afferents or Golgi tendon organ afferents on the basis of their responses to ramp-and-hold stretches, sinusoidals superimposed on ramp-and-hold stretches, maximal twitch contractions and isometric contractions and relaxations. 3. The muscle was repeatedly stretched and then either kept short or long for a few seconds followed by a slow ramp stretch. The responses of the muscle afferents to the slow stretch were compared under the two conditions. 4. Thirty out of thirty-eight units classified as primary spindle afferents and four out of eleven units classified as secondary afferents showed an enhanced response to the slow ramp when the muscle had been kept short compared to the response when the muscle had been kept long. 5. None of the eighteen Golgi tendon organ afferents showed any difference in this respect. 6. It is concluded that stretch sensitization does occur in human muscle spindles and, when present, constitutes firm evidence of the afferent originating from a muscle spindle rather than a Golgi tendon organ. In addition, due to differences in the response characteristics of primaries and secondaries, the test may aid in separating muscle spindle primary afferents from secondary afferents.

Action Potentials↗

PubMed2002

The inotropic effect of nitric oxide on mammalian papillary muscle is dependent on the level of beta1-adrenergic stimulation.

We tested the hypothesis that nitric oxide has a positive inotropic effect on mammalian cardiac muscle contractility and that this effect sums with the positive inotropic effect of beta1-adrenergic agonists when both are present. Feline right ventricular papillary muscles were stimulated to contract isometrically at 0.2 Hz in Krebs-Henseleit bicarbonate buffer (KREBS) gassed with 95% O2 and 5% CO2 (26 degrees C; pH 7.34). The nitric oxide (NO) donor, S-nitroso-N-acetylpenicillamine (SNAP, 10(-5) M), and the membrane permeable cGMP analog 8-bromoguanosine-3',5'-cyclophosphate sodium (Br-cGMP, 10(-5) M), significantly increased developed force by 13.3+/-1.5% (n = 11) and 7.8+/-2.8% (n = 7), respectively. SNAP, at 10(-5) M, significantly increased the force developed by papillary muscle treated with 10(-11) M or 10(-9) M dobutamine hydrochloride (a beta1-adrenergic agonist) (n = 25, 11.3+/-2.9% and 10.0+/-3.6%, respectively) when compared with the addition of KREBS (n = 27, 2.6+/-0.9% and 5.5+/-0.9%), but the increase was less than predicted by the sum of inotropic effects of SNAP and dobutamine. SNAP at 10(-5) M did not change developed force in muscles treated with 10(-7) M dobutamine but it significantly decreased developed force in muscles challenged with 10(-5) M dobutamine (n = 18, 29.3+/-5.0%) when compared with KREBS (n = 10, 41.5+/-6.8%). Similarly, 10(-4) M 8-bromo-adenosine cyclic 3',5'-hydrogen phosphate monosodium (a membrane permeable cAMP analog) increased developed force 14.9+/-3.3% and the addition of 10(-5) M Br-cGMP to those muscles significantly reduced developed force by 3.5%+/-1.1% (n = 7). Thus, the positive inotropic effect of NO decreased and ultimately became an attenuation as the level of beta1-adrenergic stimulation increased due at least in part, to an interaction between the cAMP and cGMP second messenger pathways.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1996

Shortening heat in slow- and fast-twitch muscles of the rat.

Shortening heat has been reported in several amphibian skeletal muscles. In this investigation, shortening heat has been investigated in both soleus and extensor digitorum longus (EDL) muscles of young rats. The procedure involved shortening the muscles through two different distances, at near maximum velocity and at the onset of a summated twitch from different initial lengths. At the end of the shortening period, the muscle contracted isometrically, and the stress and associated heat production were recorded. These heat-stress data were compared with heat-stress data of isometric twitches at different initial lengths. There was a parallel upward shift in energy output when shortening occurred, indicating the presence of a shortening heat. Shortening heat increased with the distance shortened in soleus, but this was not the case for EDL. The values for the shortening heat coefficient for both muscle types are slightly higher than those reported for amphibian skeletal muscle and suggest that shortening heat is a significant component of the energy output of mammalian skeletal muscle.

Animals↗

PubMed1999

Mechanosensitive tyrosine phosphorylation of paxillin and focal adhesion kinase in tracheal smooth muscle.

We investigated the role of the integrin-associated proteins focal adhesion kinase (FAK) and paxillin as mediators of mechanosensitive signal transduction in tracheal smooth muscle. In muscle strips contracted isometrically with ACh, we observed higher levels of tyrosine phosphorylation of FAK and paxillin at the optimal muscle length (Lo) than at shorter muscle lengths of 0.5 or 0.75 Lo. Paxillin phosphorylation was also length sensitive in muscles activated by K+ depolarization and adjusted rapidly to changes in muscle length imposed after contractile activation by either ACh or K+ depolarization. Ca2+ depletion did not affect the length sensitivity of paxillin and FAK phosphorylation in muscles activated with ACh, indicating that the mechanotransduction process can be mediated by a Ca2+-independent pathway. Since Ca2+-depleted muscles do not generate significant active tension, this suggests that the mechanotransduction mechanism is sensitive to muscle length rather than tension. We conclude that FAK and paxillin participate in an integrin-mediated mechanotransduction process in tracheal smooth muscle. We propose that this pathway may initiate alterations in smooth muscle cell structure and contractility via the remodeling of actin filaments and/or via the mechanosensitive regulation of signaling molecules involved in contractile protein activation.

Acetylcholine↗

PubMed1999

Rapid force recovery in contracting skeletal muscle after brief ischemia is dependent on O(2) availability.

We tested the hypothesis that contracting skeletal muscle can rapidly restore force development during reperfusion after brief total ischemia and that this rapid recovery depends on O(2) availability and not an alternate factor related to blood flow. Isolated canine gastrocnemius muscle (n = 5) was stimulated to contract tetanically (isometric contraction elicited by 8 V, 0.2-ms duration, 200-ms trains, at 50-Hz stimulation) every 2 s until steady-state conditions of muscle blood flow (controlled by pump perfusion) and developed force were attained (3 min). While maintaining the same stimulation pattern, muscle blood flow was then reduced to zero (complete ischemia) for 2 min. Normal blood flow was then restored to the contracting muscle; however, two distinct conditions of oxygenation (at the same blood flow) were sequentially imposed: deoxygenated blood (30 s), blood with normal arterial O(2) content (30 s), a return to deoxygenated blood (30 s), and finally a return to normal arterial O(2) content (90 s). During the ischemic period, force development fell to 39 +/- 6 (SE)% of normal (from 460 +/- 40 to 170 +/- 20 N/100 g). When muscle blood flow was restored to normal by perfusion with deoxygenated blood, developed force continued to decline to 140 +/- 20 N/100 g. Muscle force rapidly recovered to 310 +/- 30 N/100 g (P < 0.05) during the 30 s in which the contracting muscle was perfused with oxygenated blood and then fell again to 180 +/- 30 N/100 g when perfused with blood with low PO(2). These findings demonstrate that contracting skeletal muscle has the capacity for rapid recovery of force development during reperfusion after a short period of complete ischemia and that this recovery depends on O(2) availability and not an alternate factor related to blood flow restoration.

Animals↗

PubMed1995

Creep rupture of wallaby tail tendons.

The tail tendons from wallabies (Macropus rufogriseus) suffer creep rupture at stresses of 10 MPa or above, whereas their yield stress in a dynamic test is about 144 MPa. At stresses between 20 and 80 MPa, the time-to-rupture decreases exponentially with stress, but at 10 MPa, the lifetime is well above this exponential. For comparison, the stress on a wallaby tail tendon, when its muscle contracts isometrically, is about 13.5 MPa. Creep lifetime depends sharply on temperature and on specimen length, in contrast to strength and stiffness as observed in dynamic tests. The creep curve (strain versus time) can be considered as a combination of primary creep (decelerating strain) and tertiary creep (accelerating strain). Primary creep is non-damaging, but tertiary creep is accompanied by accumulating damage, with loss of stiffness and strength. 'Damage' is quantitatively defined as the fractional loss of stiffness. A creep theory is developed in which the whole of tertiary creep and, in particular, the creep lifetime are predicted from measurements made at the onset of creep, when the tendon is undamaged. This theory is based on a 'damage hypothesis', which can be stated as: damaged material no longer contributes to stiffness and strength, whereas intact material makes its full contribution to both.

Animals↗

PubMed1983

Contractile and structural reactions to impediments of Ca2+-homeostasis in Physarum polycephalum.

A combined application of 5 mM KCN and 19 microM Ca++-ionophore A-23187 leads to pronounced contractures of plasmodial strands of Physarum polycephalum. The appearance of the contractures is independent of the amount of Ca++ in the external medium. Tensiometric registrations of longitudinal contraction activity (isometric regime) reveal an average tension increase of 50 mp compared with the preceding tension level before the addition of KCN and ionophore. This high force output during the contracture coincides with a pronounced increase in the number of cytoplasmic actomyosin fibrils. Their ultrastructure is seen as a high lateral density of strictly parallel arranged F-actin filaments; the state of cytoplasmic actomyosin during this isometric contracture corresponds to the ultrastructure of isometrically contracted fibrils during the normal contraction-relaxation cycle of this organism. A simultaneous impediment of respiration and Ca++ homeostasis strongly favours a shift of the actin equilibrium to the high polymeric side in the form of fibrils and may thus be used as a preparatory step improving the specimens in the context of other investigations, e.g., for immunocytochemical investigations or for the preparation of cell-free models to be reactivated after extraction procedures.

Actomyosin↗

PubMed1984

Trigeminal nerve activity and buccal pressure as an index of total inspiratory activity in the bullfrog.

In bullfrogs with glottis occluded and lungs artificially ventilated, the buccal cavity contractors (BCconts) were found to contract isometrically, meaning that peak buccal pressure (OBP) well represents the total inspiratory nerve activities (TIAs) of BCconts. Unilateral sectioning of the trigeminal (V), hypoglossal, facial, or vagal nerve reduced the magnitude of OBP by 43.3, 28.8, 10.9, or 4.3%, respectively. The integrated peak V activity (I-ENGv) showed a linear relationship to OBP (r = 0.944) in the glottis occluded frog, but a curvilinear relationship to peak buccal pressure (peak BP) in the spontaneously breathing frog during inflation period. The latter relationship was better fitted by a hyperbolic equation (r = 0.943) than by a linear equation (r = 0.927) (p less than 0.001). The relationship between I-ENGv and peak BP showed a hysteresis during deflation period. It was suggested that both I-ENGv and peak BP can be used as a measure of TIAs, but use of the latter requires some reservations.

Animals↗

PubMed1993

[Comparison of the hand grip apex cardiography test and stress ECG for detection of patients with coronary heart disease].

It has been recently demonstrated by many authors that diastolic abnormalities of the left ventricle are the earliest mechanical manifestations of myocardial ischemia preceding both the ECG changes and angina pectoris. Recently, we have shown that using a handgrip-apexcardiographic test (HAT), one can accurately assess exercise-induced abnormalities of diastolic function in patients with angina pectoris or silent ischemia. Aim of this study is to compare the clinical value of HAT and stress-ECG in patients with prospectively documented coronary artery disease (CAD). Subject and methods 275 healthy volunteers (208 men) and 52 patients (47 men) with known (18 with prior infarction) or suspected CAD were examined. HAT and stress-ECG were performed within one month before heart catheterization. There were 17 single, 17 double, and 18 triple vessel disease patients, who showed no large dyskinesias and no wall aneurysms on angiography. Apexcardiogram (ACG) was recorded simultaneously with phonocardiogram and ECG before, during and after a low level (40% of maximal voluntary contraction) isometric stress of short duration (two minutes). As indices of diastolic function served the relative A wave to total (A/H) and to diastolic deflection (A/D) as well as the total apexcardiographic relaxation time (TART) from the onset of the aortic component of the second heart sound (A2) to the protodiastolic nadir of ACG and the TART index (TARTI) given by dividing the square root of the duration of diastolic length with TART (TARTI = square root of A2-C/TART, whereas C is the apexcardiographic onset of the systolic upstroke). Furthermore, the combined index of diastolic function DATI (diastolic amplitude time index) was calculated (DATI = TARTI/[A/D]). A pathologic or positive HAT was defined by the presence of at least one of the following recently introduced criteria: 1. A/H during and/or after handgrip > 21%, 2. TART during handgrip > TART at rest > 143 ms and/or TARTI during handgrip < 0.14, or 3. DATI during handgrip < 0.27; these limits representing the largest and lowest individual values in the controls. Complications occurred less often during HAT than during stress-ECG (angina pectoris: 4% and 25%, ventricular extrasystoles 6% and 16%, respectively). Changes of diastolic apexcardiographic indices As evident in Table 1, in the normals there were only slight, although significant, changes of TART, TARTI, DATI and A/D during handgrip; whereas A/H showed no significant changes.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗

PubMed1984

Centrally programmed patterns of muscle activity in voluntary motor behavior of humans.

Rapid voluntary limb movements are accompanied by a triphasic electromyogram (EMG): the agonist muscle discharges briefly to generate the initial limb displacement and then, in sequence, an antagonist and second agonist burst occur. The origins of these bursts of EMG have been attributed to both peripheral and central sources. We attempted to determine in human subjects whether somesthetic afferent inputs related to passive muscle stretch or joint rotation were necessary for the appearance of the three bursts. EMGs were recorded while subjects performed rapid isotonic movements before and after forearm afferent function was blocked by ischemia. EMG patterns were also studied during phasic and sustained isometric contractions of forearm muscles. When the forearm was ischemically deafferented the triphasic EMG pattern persisted though the amplitudes of the three bursts were modified. In separate experiments, a similar three burst pattern was also observed while phasic isometric contractions were performed but not when rapid-onset sustained isometric contractions were executed. These data support the view that somesthetic afferent information related to muscle length or joint rotation is not necessary for the occurrence of the three burst pattern during rapid motor behaviors. Since bursts of EMG activity were observed when torque rose and fell quickly during fast isotonic movements and phasic isometric contractions, the triphasic pattern appears to be a fundamental property of the central program underlying such rapid motor behaviors.

Adult↗

PubMed1983

Isometric training in human elbow flexor muscles. The effects on voluntary and electrically evoked forces.

The elbow flexor muscles of four men were trained using maximal voluntary isometric contractions. Thirty contractions a day were performed for five weeks. The four men and four control subjects were tested once a week: measurements of the supramaximally stimulated isometric twitch force, the time taken for the twitch force to peak and the tetanic force were carried out; simultaneously, measurements of the force of maximal voluntary isometric contraction and resistance to fatigue were made. The testing sessions produced no training effect on control subjects. Training produced a 20 per cent increase in the force of maximal voluntary isometric contraction after five weeks, but the forces of electrically evoked twitch and tetanus showed no increase. It was concluded that the increase in the force of maximal voluntary isometric contraction must be related to factors other than the force-generating capacity of the muscle fibres themselves.

Adult↗