Calcium efflux and spontaneous activity of frog sinus venosus and isotonic sucrose solution.
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Animals↗
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Results for “Isotonic Contraction”
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A comparison of isotonic and isometric exercised performed on contralateral limbs.
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Adult↗
[Protective effects of perindopril in an experimental model of cardiomyopathy].
The effects of an angiotensin converting enzyme (ACE) inhibitor on the intrinsic contractility of the myocardium in cardiac failure have not been studied intensively. The authors studied inotropism, lusitropism and economy of contraction in vitro on left ventricular papillary muscle preparations of cardiomyopathic Syrian hamsters (CSH) treated preventively with perindropil, i.e. before overt signs of cardiac failure. The CSH of the dilated Bio 53.58 strain aged 1 month were treated with perindropil 1 mg/Kg/day for 5 months (PE, N = 11) or with placebo (PL, N = 11) and control hamsters of the F1B strain received placebo (C, N = 7). Compared with C, PL had a significant reduction of the maximal velocity of contraction Vmax (p < 0.01) and of total isometric tension (TF/mm2), p < 0.05, and a reduction of the G curve of the hyperbolic Hill Force-Velocity relationship (p < 0.01). The G value is usually greater in models with improved economy of contraction. When compared with PL, PE showed a 68% inhibition of the plasma activity of ACE, a better Vmax (p < 0.05) but an unchanged TF/mm2. The G value was less depressed than that of C (p < 0.05). The velocity of isotonic relaxation (maxVL) and the negative peak of the derivative of the isometric force (-dF/dt max) were significantly lower in the PL than in the C group but these lusitropic abnormalities remained coordinated with those of the contraction phase, indicating the absence of an intrinsic effect on relaxation in cardiomyopathy. Perindopril prevented the reduction of maxVL but not that of -dF/dt max.(ABSTRACT TRUNCATED AT 250 WORDS)
Angiotensin-Converting Enzyme Inhibitors↗
Activation energy of ventricular contraction in anionicaliy modified solutions.
The activation energy of ventricular contraction and relaxation in chloride and nitrate-Ringer's solution was studied on the driven rat ventricle strip by measurement of the specific contraction and relaxation velocities over a 17 degrees C range of temperature. Nitrate ion produced a small but significant reduction in the activation energy of contraction.
Animals↗
Simultaneous modulation of the exteroceptive suppression periods in the trapezius and temporalis muscles by experimental muscle pain.
OBJECTIVE: To investigate whether the exteroceptive suppression (ES) periods in the trapezius and temporalis muscles could be simultaneously modulated by either experimental trapezius muscle pain or temporalis muscle pain. METHODS: Fourteen healthy volunteers participated in two sessions with randomised injections of either hypertonic or isotonic saline into the right trapezius muscle or right temporalis muscle. The pain intensity was continuously scored on a 10 cm electronic visual analogue scale. During muscle contraction, the early (ES1) and late (ES2) reflex in the temporalis and late (ES2) reflex in the trapezius elicited by electrical stimulation of the right infraorbital nerve were recorded pre-, during-, and post-injection. RESULTS: Hypertonic saline injection induced local muscle pain and referred pain with the maximal pain intensity of 6.3+/-0.5 cm in the right trapezius and 6.7+/-0.6 cm in the right temporalis muscles. Injection of either hypertonic or isotonic saline into the right trapezius muscle was associated with significantly shortened ES2 duration and offset time in the injected right trapezius muscle. Only injection of hypertonic saline into the right trapezius muscle could significantly reduce the ES2 offset time and decrease the degree of suppression of ES2 in the right temporalis and left trapezius muscles. Injection of either hypertonic or isotonic saline into the right trapezius muscle evoked no changes in ES2 parameters in the left temporalis muscle. Injection of hypertonic saline, but not isotonic saline, into the right temporalis muscle caused a significantly shorter ES2 offset time and shorter ES2 duration bilaterally in the temporalis and trapezius muscles. CONCLUSIONS: The findings of the present study provide evidence for a bi-directional effects reflecting convergence of muscle afferents from the trigeminal and upper cervical neural systems in humans, which may partly underlie the manifestations of pain referral between these two areas.
Adult↗
[Dynamics of the efferent regulation of muscle contraction. Analysis of transition processes: frequency of efferent stimulation--muscle length].
Transition processes of the length changes were studied in the ankle extensors of anesthetized cats. The processes were evoked under isotonical conditions by step changes in frequency of distribution stimulation of the efferents supplying these muscles. The system dynamics was essentially nonlinear because the time constants of the processes were dependent on amplitudes and sign of the input signal. The time constants abruptly decreased when the sign of the length changes alternated from minus to plus and continuously decreased when amplitude of the transition process rose in the absolute value. The time constants for the transition processes were 1.15 +/- 0.09 s for soleus shortening and 0.40 +/- 0.07 s for its lengthening. The same parameters in fast muscles were 0.51 +/- 0.085 for shortening and 0.21 +/- 0.04 s for lengthening. These time constants are very close to the parameters of the transition processes: external load-muscles length. The observed properties of the muscles are discussed for their functional significance.
Animals↗
The relative activation of elbow-flexor muscles in isometric flexion and in flexion/extension movements.
Coordination studies of multi-joint movements suggest that the central nervous system uses some constraints to reduce the large number of degrees of freedom of the arm. To gain insight into how the net joint torque is distributed among the muscles, intramuscular EMG recordings were made to determine the relative activation of five major elbow-flexor muscles during isometric, shortening, and lengthening contractions at three elbow joint angles. A regularization procedure was used to evaluate the effect of two different approaches used to calculate the relative contribution of elbow-flexor muscles to joint torque from intramuscular EMG recordings. The results demonstrate a significant increase of the relative contribution of the biarticular muscles for more extended elbow joint angles and for isotonic tasks relative to isometric tasks.
Adult↗
Intraoperative image-directed dye marking of tumor margins.
The incorporation of interactive image guidance during intracranial tumor surgery offers the possibilities of reduced operative trauma, shorter operation time, greater precision, and an increased understanding of complex anatomy and pathology. A basic weakness with these systems though is that they cannot account for movement of target points due to brain shift by draining of CSF or removal of pathology during the operative procedure. We have developed a stereotactic (frameless) guided injector probe for marking the tumor boundary with dye injection in conjunction with a neuronavigation system. The device consisted of a rigid blunt hollow probe (2 mm dia.) with 4 small side holes at the tip. The catheter is mounted in a holder equipped with 3 LEDs supplying guidance information for the neuronavigation system. A small manual aliquoting pump delivers a measured amount of dye in each track. Isotonic methylene blue was injected in 6 to 8 tracks around the periphery of the tumor as determined by the contract ring in MR scans. The dye was injected using image-directed guidance before resection of the tumor was started (often with the dura intact). Tumor tissue could then be resected until the dye became visible at the tumor boundary. Identification of the dye in the tissue was enhanced with the use of the operating microscope. The 3-dimensional position of the dye track could be determined at the end of tumor resection and compared with its initial position giving a good estimate of local brain shift. The method has proved especially helpful for the resection of large gliomas allowing for a more radical operative result.
Aged↗
The effects of iodixanol and iopamidol on hemodynamic and cardiac electrophysiologic parameters in vitro and in vivo.
Iodixanol is a new, nonionic, dimeric contrast medium which, in concentrations appropriate for radiographic use, is hypotonic with respect to plasma. The purpose of these in vivo and in vitro studies was to compare the effects of iopamidol, iodixanol formulated to isotonicity with sodium salts (sodium formulation), and iodixanol formulated to isotonicity with sodium, calcium, and magnesium salts (cationic formulation) on hemodynamic and electrophysiologic parameters. In vitro, the spontaneous rate of contraction by guinea pig right atrial and force development by right ventricular papillary muscles were evaluated in the presence of 1% to 100% (v/v) of the three contrast media. Iopamidol significantly (P less than .05) decreased the rate of atrial contraction to a greater extent than either formulation of iodixanol. Iopamidol decreased papillary muscle force development more than the sodium formulation of iodixanol (P less than .05). The cationic formulation of iodixanol had little effect (less than 30% change) on papillary muscle force development at concentrations up to 100%. The contrast media were also injected into the left coronary arteries of open-chest, anesthetized dogs at 0.8 mL/second for 5 to 30 seconds. All contrast media increased (P less than .05) systolic blood pressure (SBP), mean arterial pressure (MAP), and peak left ventricular pressure (LVP). Iopamidol increased LVP and LV end diastolic pressure to a greater extent (P less than .05) than the cationic formulation of iodixanol. We conclude that iopamidol affected cardiovascular parameters more than iodixanol.
Animals↗
Effect of airway inflammation on smooth muscle shortening and contractility in guinea pig trachealis.
We studied the effect of either 1) immunogenic inflammation caused by aerosolized ovalbumin or 2) neurogenic inflammation caused by aerosolized capsaicin in vivo on guinea pig tracheal smooth muscle (TSM) contractility in vitro. Force-velocity relationships were determined for nine epithelium-intact TSM strips from ovalbumin-sensitized (OAS) vs. seven sham-sensitized controls and TSM strips for seven animals treated with capsaicin aerosol (Cap-Aer) vs. eight sham controls. Muscle strips were tethered to an electromagnetic lever system, which allowed isotonic shortening when load clamps [from 0 to maximal isometric force (Po)] were applied at specific times after onset of contraction. Contractions were elicited by supramaximal electrical field stimulation (60 Hz, 10-s duration, 18 V). Optimal length for each muscle was determined during equilibration. Maximal shortening velocity (Vmax) was increased in TSM from OAS (1.72 +/- 0.46 mm/s) compared with sham-sensitized animals (0.90 +/- 0.15 mm/s, P < 0.05); Vmax for TSM from Cap-Aer (0.88 +/- 0.11 mm/s) was not different from control TSM (1.13 +/- 0.08 mm/s, P = NS). Similarly, maximal shortening (delta max) was augmented in TSM from OAS (1.01 +/- 0.15 mm) compared with sham-sensitized animals (0.72 +/- 0.14 mm, P < 0.05); delta max for TSM from Cap-Aer animals (0.65 +/- 0.11 mm) was not different from saline aerosol controls (0.71 +/- 0.15 mm, P = NS). We demonstrate Vmax and delta max are augmented in TSM after ovalbumin sensitization; in contrast, neurogenic inflammation caused by capsaicin has no effect on isolated TSM contractility in vitro. These data suggest that airway hyperresponsiveness in vivo that occurs in association with immunogenic or neurogenic inflammation may result from different effects of these types of inflammation on airway smooth muscle.
Aerosols↗
Mechanical properties of carotid arteries from DOCA hypertensive swine.
Carotid arteries from control and deoxycorticosterone acetate (DOCA) hypertensive swine were examined for alterations in structure and in contractile properties. Vessels were excised 7 weeks after subcutaneous implantation of the steroid and subsequent elevation in mean arterial pressure from 102 to 133 mm Hg. The carotid media was 1.8 times thicker in arteries from hypertensive animals than in arteries from control animals. This enlargement was associated with an increase in muscle mass, as the fraction of the media composed of smooth muscle cells remained unchanged. Maximal active stress induced by several agonists normalized for cell cross-sectional area was unaltered. No change was observed in sensitivity or maximal response to norepinephrine, histamine, or KCl depolarization. Isotonic shortening rates were also comparable, as was the time course of shortening velocity to a constant afterload during tonic contractions. It is concluded that an enlargement of the carotid media develops in this model of hypertension. However, this response is not associated with detectable alterations in contractile system function.
Animals↗
Light-evoked contraction of the photosensitive iris of the frog.
Smooth muscle cells of the frog iris sphincter contain rhodopsin and contract in response to light. The mechanism of light-evoked contraction was studied with particular attention paid to the role of calcium. The contractile proteins of the sphincter smooth muscle cell can be activated by an increase in intracellular calcium. Light-evoked contraction, however, is not accompanied by a measurable change in membrane potential and occurs in the absence of extracellular Na+ and/or Ca2+, as well as in the presence of isotonic KCI. Maximum light-evoked tension is reduced by exposure to Ca2+-free solutions containing EGTA and high K+ and is restored by incubation in solutions containing Ca2+. The restored response, which persists after return to Ca2+-free solution, depends on the concentration of Ca2+ in the incubating solution and on the duration of the incubation. The results support the conclusion that light produces contraction of the iris sphincter by causing the release of Ca2+ from an intracellular storage site.
Animals↗
Effect of gastrin-releasing peptide (GRP) on guinea pig gallbladder contraction in vitro.
Few studies have reported the effects of gastrin-releasing peptide (GRP)/bombesin on the guinea pig gallbladder, and the results are contradictory. Because such contradictory results may, in part, be due to technical factors, we investigated the effect of GRP on guinea pig gallbladder smooth muscle, using an improved horizontal organ bath. The guinea pigs were killed and the gallbladder was removed. Four longitudinal muscle strips (2 x 12 mm) were suspended in Krebs-Ringer solution at 37 degrees C and aerated with 95% O2 and 5% CO2. The mechanical activity of the strips was recorded isotonically by displacement-voltage transducers, via L-arms, to which a piezoelectric element with a frequency of 100 Hz and movement of 50 microns was applied. GRP contracted gallbladder muscle strips dose dependently, but the calculated maximal response was 22.4% and 20.1% of the acetylcholine- and cholecystokinin octapeptide (CCK8)-induced responses, respectively. The GRP-induced contraction was unaffected by the muscarinic blocker, atropine, or by the CCK receptor antagonist, loxiglumide. It is concluded that GRP weakly, but apparently directly, stimulates guinea pig gallbladder contraction.
Acetylcholine↗
Effects of isokinetic, isotonic and isometric submaximal exercise on heart rate and blood pressure.
The purpose of the present study was to compare arterial pressure (AP) and heart rate (HR) responses to submaximal isokinetic, isotonic and isometric exercises currently employed in physical rehabilitation therapy in terms of both magnitude and time-course. To this aim AP and HR were continuously and noninvasively measured in ten healthy subjects performing isokinetic, isotonic and isometric exercises at the same relative intensity. Isokinetic and isotonic exercises consisted of 30 knee extension/flexion repetitions at 40% of maximal effort. Isokinetic speed was set at 180 degrees s(-1). Isometric exercise consisted of a 60-s knee extension at 40% maximal voluntary contraction. The AP showed a rapid and marked increase from the onset of all types of exercise progressing throughout the exercises. Peak systolic (SAP) and diastolic (DAP) arterial pressure were 190.7 (SEM 8.9) and 121.6 (SEM 7.8) mmHg during isokinetic and 197.6 (SEM 11.2) and 128.3 (SEM 7.7) mmHg during isotonic exercise, respectively. During isometric exercise peak SAP and DAP were 168.1 (SEM 6.3) and 102.1 (SEM 3.7) mmHg, respectively [both lower compared to isokinetic and isotonic exercise (P < 0.05)]. The HR rose abruptly and after five isokinetic and isotonic repetitions it had already increased by about 30 beats min(-1), continuing to rise throughout the exercises. The HR response to isometric exercise was significantly less (P < 0.05) at all times. An immediate fall in AP, undershooting resting levels, was observed at the cessation of all types of exercise, being more marked after isokinetic and isotonic exercise. These results indicate that submaximal exercise of a dynamic type induces greater AP responses than intensity-matched isometric exercise and that even submaximal endurance-type rehabilitation exercise yields an elevated functional stress on the cardiovascular system which could precipitate hazardous events particularly in subjects with unrecognized cardiac diseases.
Adult↗
[Contraction of the muscle fiber during propagation of excitation].
One-dimensional contraction propagating in a muscle fibre with prescribed load is considered theoretically. The analysis is based on the general model of continuous medium with mechanochemical reactions. Deformations and displacements in isotonic regime are calculated for two modes of stimulation: at the end point of the fibre or at some its intermediate point. Possible applications of the results to a cardiomyocyte are discussed in Addendum.
Animals↗
Decreased PO2 and rabbit aortic smooth muscle mechanics.
Rabbit thoracic aorta was used to determine the effects of decreasing PO2 on the mechanical properties of contractions in response to norepinephrine (NE) and KCl. Aortae were aerated with 45% O2/5% CO2/50% N2 and stimulated with 10 microM NE or 50 mM KCl. At 5 min of stimulation, 5% CO2/95% N2 aeration was introduced for 15 min, defined as hypoxia. This time period was previously shown to produce similar decrease in [ATP] in either stimulation condition. Force, stiffness and isotonic shortening velocity were monitored during the initial stimulation, during hypoxia and during re-oxygenation. Hypoxia produced a substantial and rapid decrease in force and a concomitant decrease in stiffness during NE stimulation; delayed and smaller decreases in force and stiffness were observed during KCl stimulation. The force-stiffness relationship was steeper during KCl than NE stimulation, and hypoxia did not affect these relationships. Isotonic shortening velocity was significantly depressed by hypoxia during both stimulations although the decrease during KCl stimulation required a longer time. These data demonstrate that relaxation of an agonist-induced contraction in response to hypoxia results from a decrease in the number of activated crossbridges and not formation of rigor bridges.
Animals↗
Characterisation of detrusor contractile function in relation to old age.
This report describes an age-related clinical study of detrusor muscle function using urodynamic data obtained from 1391 women and 324 men of different age groups who were free from overt neurological disease and diabetes. Isometric detrusor function during unstable activity was assessed by integrating the calculated force of unstable detrusor activity during filling of the bladder. Isotonic voiding activity was measured by calculating the velocity constant Q*, which reflects the speed of detrusor muscle shortening. In addition, the change in detrusor pressure on initiation of voiding and the post-micturition residual urine volume were recorded. Older patients of both sexes had higher residual urine volumes. Older women showed lower detrusor shortening velocities. There were no age-related differences in isometric detrusor function. Older women showed a tendency for the detrusor contraction to fail on initiation of voiding, whereas older men did not demonstrate this difference. Voiding dysfunction in late life was more marked amongst women and seemed to be related to a failure of isotonic detrusor function with no related changes in isometric function.
Adult↗
Hepatitis B in St Petersburg, Russia (1994-1999): incidence, prevalence and force of infection.
Hepatitis B (HB) is thought to be an expanding health problem in Russia. The incidence of infection was estimated from mandatorily reported HB cases in St Petersburg. The two-sided t-test for independent samples and the LOESS (locally-weighted regression) smoother were used to compare the age at infection for symptomatic, asymptomatic and chronic infections, by gender. The force of infection was estimated from seroprevalence data (907 sera taken in 1999) using a newly developed nonparametric method based on local polynomials, as well as an earlier method based on isotonic regression and kernel smoothers. With the local polynomial method, pointwise confidence intervals (95%) were constructed by bootstrapping. On average, men contracted HB infection at a significantly younger age than women (in 1999, 21.8 vs 22.7 years, respectively). The overall male to female ratio was 1.92. In 1999 the overall incidence almost doubled compared with the preceding years and tripled among the age groups with highest incidence (15-29-year olds: 85% of cases in 1999). The incidence increase was associated with a lower average age at infection (24.1 years in 1994 vs 22.1 years in 1999). The age and gender-specific force of infection estimates generally confirmed the incidence estimates and emphasized the usefulness of local polynomials to do this. Hence HB transmission in St Petersburg occurs mainly in young adults. The dramatic increase of infections in 1999 was probably due to injecting drug use. Without intervention, HB virus is expected to continue to spread rapidly with a greater proportion of female infections caused by sexual transmission. These trends may also provide an indication for HIV transmission.
Adolescent↗