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Results for “Isometric Contraction”

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PubMed1982

Effect of nickel ions on spontaneous, electrically and norepinephrine stimulated isometric contractions in the isolated portal vein of the rat.

The effect of low concentrations (1-10 microM) of nickel (Ni2+) was studied on the spontaneous contractile activity of isolated rat portal vein preparations. To distinguish between presynaptic and postsynaptic actions, Ni2+-induced changes of isometric force development evoked either by electrical field stimulation (80V/5 cm; 1 msec; 1-32 Hz) or by exogenous norepinephrine (NE) were compared. Ni2+ inhibited spontaneous isometric force development, decreased basal tone but significantly increased the frequency of contractions. The experimental findings that inhibition of the effect of selective stimulation of adrenergic nerves was significantly more pronounced than the depression of contractions evoked by exogenous norepinephrine indicate that in addition to postsynaptic actions, Ni2+ influences presynaptic mechanisms (i.e. NE-release) in this vessel preparation.

Animals↗

PubMed1986

An evaluation of contractility parameters determined from isometric contractions and micturition studies.

In a group of 110 patients of mixed pathology 218 micturitions were investigated. Using an on-line computer, two contractility parameters were calculated: the parameter U/l, which is derived from the isometric pressure rise in the detrusor before micturition actually started, and the parameter wmax, which is derived from flow and pressure during micturition. It was found that neither of the parameters conforms to the definition of an ideal contractility parameter. Both parameters are subject to the influence of the urethral resistance or the degree of neurogenic stimulation of the bladder, and both measure to some degree the actual performance of the detrusor during a given micturition instead of its myogenic properties. Nevertheless, by dividing patients into groups according to these two measured values, it was shown that clinically relevant types of detrusor behaviour can be distinguished.

Adult↗

PubMed1982

Effect of muscle stretch during isometric contraction on the time-course or relaxation in mammalian myocardium.

The effect of stretch on the time-course of relaxation has been investigated in rat papillary muscle. In control conditions, a quick stretch carried out at or after the peak of an isometric twitch promotes an earlier and faster relaxation. Following inotropic interventions which decelerate the activation decay rate (caffeine addition and Ca2+ replacement with Sr2+) the onset and time-course of relaxation are unaffected by the stretch.

Animals↗

PubMed1976

Relationship between initial chemical reactions and oxidative recovery metabolism for single isometric contractions of frog sartorius at 0 degrees C.

1. Measurements of intitial chemical changes and recovery oxygen consumption (deltaO2) were made in unpoisoned aerobic frog sartorius muscles at 0 degrees C to provide independent measures of the chemical energy used for isometric tetani of various durations. 2. DeltaO2 was measured polarographically and increased in a curvilinear fashion with stimulus duration. For stimulations longer than 4 sec deltaO2 was a linear function of the tension-time integral. 3. Measurements of the changes in the content of phosphorylcreatine, 'free' creatine and inorganic phosphate were made in muscles rapidly frozen during a tetanus. The average of these quantities, delta approximately P, was used to measure the initial 'high energy' phosphate utilization. No break-down of 'high-energy' phosphate compounds was detected up to 200 sec after relaxation of tension. Changes in the content of ATP were not observed except for a small decrease (-0-25+/-0-1 mumole/g) in muscles tetanized for 1 sec. 4. Delta approximately P also increase curvilinearly with tetanus duration and, for tetanic durations greater than 4 sec, was a linear function of the tension-time integral. 5. Both deltaO2 and delta approximately P were quantitatively related by a constant scaling factor of about 4-3 (delta approximately P/deltaO2) throughout the range of tetanic durations studied. The constancy of this ratio.provides evidence against the hypothesis that a significant 'missing reaction' provides energy during any one portion of the tetanus. Several hypothesis may account for the numerical value of the ration delta approximately P/deltaO2.

Adenosine Triphosphate↗

PubMed1986

Increased sensitivity of the isometric contraction of the neonatal isolated rat atria to halothane, isoflurane, and enflurane.

Isolated atria from neonatal (0-5 day old) and adult (50 +/- 5 day old) rats were perifused in oxygenated Kreb's Henseleit solution at 30 +/- 0.5 degrees C and exposed to four different concentrations of halothane, isoflurane, or enflurane while isometric contractile tension was recorded and compared with control atria. ED50 values (mM of anesthetic required to produce 50% reduction in contractile tension) of neonates for halothane (0.18 +/- 0.01), isoflurane (0.41 +/- 0.05), and enflurane (0.41 +/- 0.04) were significantly lower than those of adults (0.35 +/- 0.02, 0.80 +/- 0.05, and 1.15 +/- 0.05, respectively). Furthermore, neonatal ED50 calculated as per cent of adult ED50 was significantly less for enflurane (35%) than for halothane (54%) or isoflurane (51%).

Action Potentials↗

PubMed1998

Myosin head movements during isometric contraction studied by X-ray diffraction of single frog muscle fibres.

Time resolved X-ray diffraction experiments in single muscle fibres of the frog at 2.15 microns sarcomere length and 4 degrees C were performed at ID2 (SAXS), ESRF, Grenoble (France) to investigate the structural aspects of cross-bridge action during the development of the isometric tetanic tension (T0). Changes in the low angle myosin-based reflections were measured with 5 ms time resolution by signal averaging data collected with a 10 m camera length and a 2D gas-filled detector. Upon activation the intensity of the first order myosin layer line reflection, I(M1), and the intensity of the second order meridional reflection, I(M2), reduced practically to zero with a half-time which leads the tension rise by 15-20 ms. The complex changes of the intensity of the third order myosin meridional reflection, I(M3), and the increase of its axial spacing from 14.34 nm (at rest) to 14.57 nm (at T0) could be analysed by assuming that they were the result of the combination of the time dependent modulation in intensity of two closely spaced periodicities, one at 14.34 nm, characteristics of the myosin molecule at rest and the other at 14.57 nm, assumed by the myosin as a consequence of the activation and force production. I(14.34) drops monotonically in advance to isometric tension development with a half-time similar to that of I(M1) and I(M2), while I(14.57) rises from zero to a maximum in parallel with tension.

Animals↗

PubMed1975

Relation of activity in precentral cortical neurons to force and rate of force change during isometric contractions of finger muscles.

The activity of single neurons within the hand area of the precentral motor cortex of primates was recorded during the performance of a maintained precision grip between the thumb and forefinger. The finger opposition forces were exerted against a strain gauge which allowed force changes to be studied under near isometric conditions. Task performance required the generation of a force ramp (the dynamic phase) and thereafter the maintenance of a stable force for one second (the static phase). Intracortical stimulation through the recording electrode was used to verify that the recordings were made from the appropriate somatotopographic area of the motor cortex. From a total of 221 recorded neurons, 76 were found to be either activated or deactivated during performance of the task. Among the 51 activated neurons, most discharged at higher frequencies during the dynamic phase, than during the static phase. The discharge of some of these neurons could be related to both force (F) and rate of force change (dF-dt) whereas certain others could only be correlated with dF-dt. The change in discharge frequency for these neurons generally occurred prior to the onset of EMG activity. Eight neurons were more active during maintained force than during the force ramp. The discharge frequency could not be correlated with dF-dt and only one showed a significant positive relation to force. The change in discharge frequency for these neurons either coincided or occurred after the onset of EMG activity.

Animals↗

PubMed1976

Motor unit differentiation and integrated surface EMG in voluntary isometric contraction.

The role of the differentiation of motor units (MU's) in the relation between integrated surface electromydgram and force was studied here for the biceps brachii, in the course of static contraction in man. The global EMG of the biceps brachii was recorded by two silver electrodes fixed to the skin. The MU's activity was simultaneously lead off by three bipolar wire electrodes inserted in three points of the muscle. MU firing frequency and recruitment were estimated by counting the action potentials on the three elementary records. The comparison between the increase of the integrated surface EMG and MU recruitment as a function of force shows that MU recruitment in itself cannot account for the increase in the integrated global EMG, particularly for high values of force. The difference between MU recruitmentand integrated global EMG, which can neither come from a possible MU's synchronisation as was shown in the discussion, is being suggested to be connected to the progressive firing of "phasic" MU's. This type of recruitment may also play an important role in the gradation of isometric force in normal man.

Action Potentials↗

PubMed1973