Isometric contraction, isotonic contraction and passive contraction in smooth muscles.
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Animals↗
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Fatigue of mouse diaphragm muscle in isometric and isotonic contractions.
Fatiguabilities of mouse diaphragm muscle in vitro in isometric and isotonic contractions were compared in this study. Isolated mouse diaphragm muscle was stimulated repetitively to induce fatigue during both isometric and isotonic contractions. The supramaximal electrical stimulation used was a train of 100-Hz, 0.5-ms pulses delivered to the muscle every 2 s for 0.5 s. The percentage decrease in isometric tension from beginning to end of the fatiguing process was used as the index of fatigue. The experiments were carried out at different PO2 levels in both normal and zero-glucose Ringer solutions. It was found that fatigue developed more rapidly in isotonic contractions than in isometric ones. Also, the extracellular glucose level demonstrated little effect on the muscle's short-term fatiguability, whereas reductions in the extracellular PO2 exerted a profound effect, especially in the case of isotonic fatigue.
Aerobiosis↗
The effects of isotonic contractions on the rate of fatigue development and the resting membrane potential in the sartorius muscle of the frog, Rana pipiens.
The goal of this study was to characterize how isotonic contractions affect the rate of fatigue development. Muscle bundles dissected from frog sartorius muscles were stimulated with 100-ms long train of pulses (0.5 ms, 6 V, 140 Hz). To measure the effect of the isotonic contractions, isometric tetanus were elicited at regular time intervals during the stimulation to fatigue. In general, isotonic contractions caused a faster decrease in tetanic force than isometric contractions. The difference in tetanic force between an isotonic and isometric fatigue increased gradually over a 20-min period to 7.9 and 13.5% at 0.04 and 0.1 trains/s (TPS), respectively. At 0.2, 0.5, and 1.0 TPS, the decrease in tetanic force was also faster during an isotonic fatigue, which resulted in an initial difference in tetanic force between the two types of fatigue. The difference did not exceed 18.5% and did not persist throughout the stimulation period; i.e., the difference disappeared before the end of the fatigue stimulation. The half-relaxation time was prolonged during fatigue development, and the prolongation was greater during an isotonic fatigue, except at 0.04 TPS. The increases in the half-relaxation time at 0.2, 0.5, and 1.0 TPS were followed by a decrease, and the decreases were especially pronounced during an isotonic fatigue at 0.5 and 1.0 TPS. The results showed for the first time that isotonic contractions cause a faster rate of fatigue development in frog sartorius muscles, and this effect depends on the frequency of stimulation.
Animals↗
Structural changes in smooth muscle cells during isotonic contraction.
Smooth muscle cells of the guinea-pig taenia coli were studied in light and electron microscopy, in condition of mild stretch or of isotonic contraction. During contraction the cells increase in transverse sectional area and their packing density passes from 94,000-mm-2 to 18,000-mm-2. The percentage increase in transverse sectional area of the taenia is approximately the same as the percentage decrease in length. Measurements of cell transverse sectional area suggest that the individual cells shorten and fatten more than the taenia as a whole. Whereas stretched muscle cells run parallel to each other and show a fairly smooth surface, isotonically contracted cells are twisted and entwine around each other. Their surfaces are covered with myriad processes and folds. Longitudinal, transverse or oblique stripes are seen in light microscopy in the contracted muscle cells and it is suggested that they are related to the characteristics of the cell surface. In electron microscopy a complex pattern of interdigitating finger-like and laminar processes is observed. Caveolae are mainly found on the evaginated parts of the cell surface, dense patches are mainly (but not always) found on the invaginated parts. Desmosome-like attachments between contracted cells are frequent. The collagen fibrils run approximately parallel to the stretched muscle cells; on the other hand, they run obliquely and transversely around the isotonically contracted cells.
Animals↗
[Isotonic contraction of rabbit superior rectus muscle].
It is well known that the mammalian extraocular muscle has slow muscle fiber morphologically. But the contraction speed of slow muscle fiber has not been mentioned in previous reports. We studied the isotonic contraction of slow muscle fiber and compared it with fast muscle fiber. Each fiber bundle was isolated from the rabbit superior rectus muscle. Both light microscopic findings and the reaction to isotonic contraction in Ca2+ free Ringer's solution could identify each of the two muscle fiber types. Contraction speed depended on the frequency of stimuli (40-200 Hz) in both slow and fast muscle fiber. Maximum velocities of slow and fast fiber bundles were 4.3 +/- 1.53 mm/sec and 26.9 +/- 3.48mm/sec at 200Hz, respectively. It was suggested that the relaxation of slow muscle fiber did not interfere with the contraction of the fast muscle fiber. The relation between contraction velocity and afterload showed an approximately right angle hyperbolic curve.
Animals↗
Energy production in cardiac isotonic contractions.
The energy output of rabbit papillary muscle is examined and it is shown that there is more energy liberated in an afterloaded isotonic contraction than in an "equivalent" isometric contraction. This statement holds true regardless of whether equivalence is based on the proposition that tension or the time integral of tension is the best index of muscle energy expenditure. Besides the external work performed there is additional heat production in isotonic contractions and this heat increases as the afterload is decreased. The additional heat is more evident when tension rather than the time integral of tension is made the determinant of energy expenditure. It is shown in single contractions that the rate of isotonic heat production, regardless of afterload size, never exceeds the heat rate recorded in an isometric contraction at the same initial length. Experiments reveal no simple linear correlation between isotonic energy output and contractile element work. Problems associated with the compartmentalization of the energy output of a contraction are discussed.
Analysis of Variance↗
[Isotonic contraction and contracture of the isolated right rat ventricle. Effect of La3+, prenylamine, ATP, Mg2+ (author's transl)].
1. The isolated right rat ventricle was immersed in Tyrode solution (25) ml) and stimulated electrically at a frequency of 60/min. Changes in the amplitude of isotonic contractions and contractures were assessed. 2. Isotonic contractions were reduced (after Prenylamine, ATP, Mg), or suppressed (by LaCl3 = 10 mM). Contracture was caused by Prenylamine (4 mg/25 ml Tyrode solution or more). 3. Addition of 100 mM KCl (NaCl reduced equimolarily to 37 mM did not influence contracture in the presence of the investigated substances with the exception of MgCl2 = 10 to 15mM, where only the rate of development of potassium contracture was reduced. 4. After previous immersion of the tissue in the presence of LaCl3 - 10 mM and Prenylamine 1-4 mg/25 ml Tyrode solution the contracture developed after removal of NaCl (substitution by sucrose 270 mM), which, however, declined after addition of NaCl only when previously treated with Prenylamine and not when treated with La. 5. Addition of 100 mM KCl (naCl reduced to 37 mM) after previous immersion of the tissue in the presence of the investigated substances caused contracture the rate of rise of which was smaller after La than in controls: after the remaining substances it did not differ. 6. Reduction of the contracture after reduction of KCl from 100 to 5.6 mM developed only after previous immersion of the tissue in the presence of ATP and Mg and not after previous immersion in the presence of Prenylamine and La. 7. The results are compared with biochemical findings. They suggest a shift of contractile Ca in the heart.
Adenosine Triphosphate↗
Ca2+-dependent facilitated shortening in isotonic contraction of trachealis muscle.
We compared isotonic shortening with isometric force generation as a function of external Ca2+ in 166 tracheal smooth muscle (TSM) strips from 27 mongrel dogs in vitro. Concentration-response curves were generated with muscarinic stimulation (acetylcholine, ACh), alpha-adrenergic receptor activation (norepinephrine after beta-adrenoceptor blockade, NE), serotonin (5-HT), and KCl-substituted Krebs-Henseleit solution. The concentrations of 5-HT causing half-maximal shortening (ECS50, 1.54 +/- 0.14 X 10(-7) M) and half-maximal active isometric tension (ECT50, 1.72 +/- 0.30 X 10(-7) M) were similar (P = NS). Likewise, ECS50 (21.9 +/- 0.7 mM) and ECT50, (22.0 +/- 0.9 mM) were similar for KCl. In contrast, facilitated isotonic shortening (i.e., greater isotonic shortening for comparable degrees of force generation) was elicited with ACh and NE for all levels of force generation between 15 and 85% of maximum and for all concentrations of ACh from 3 X 10(-8) to 3 X 10(-5) M (P less than 0.05 for all points). Facilitated isotonic shortening also was elicited for all concentrations of NE from 10(-8) to 10(-6) M (P less than 0.05 for all points). Removal of Ca2+ from the perfusate substantially reduced the potency of ACh (P less than 0.001) and abolished differences between ECS50 (2.23 +/- 0.28 X 10(-5) M) and ECT50 (2.50 +/- 0.46 X 10(-5) M, P = NS). We demonstrate that for comparable degrees of force generation, muscarinic and alpha-adrenergic receptor activation cause greater isotonic shortening than KCl or 5-HT and that this facilitated shortening is associated with the concentration of external Ca2+.
Acetylcholine↗
Indices of myocardial oxygen consumption for isotonic contraction.
To investigate the model-independent mechanical determinants of energy expenditure, a respirometer was constructed to study isolated feline papillary muscles. Mechanical parameters recorded were the distance of shortening (deltaL), peak velocity of shortening (Vp), mean velocity of shortening (V), tension-time index (TTI), afterload (P), and the integral of the contraction portion of the phase plane trajectory of velocity and length (integral of VdL). Oxygen consumption (Vo2) during 15-min isotonic contraction periods was monitored with a polarographic electrode. Vp, V, and delta L were inversely related to Vo2 in a curvilinear manner. P and TTI were directly related to Vo2 in a curvilinear fashion. Integral of VdL was inversely related to Vo2 in a linear manner. In several experiments the contractile state of the muscles was augmented by addition of norepinephrine (7 X 10(-8) M). The relationship between integral of VdL and Vo2 was shifted above and parallel to that for the control muscles. These experiments indicate that the index integral of VdL is linearly related to the oxygen consumed in isotonic contraction of isolated mammalian ventricular myocardium at a given level of contractile state.
Animals↗
Force-velocity shifts with repetitive isometric and isotonic contractions of canine gastrocnemius in situ.
The force-velocity (F-V) relationships of canine gastrocnemius-plantaris muscles at optimal muscle length in situ were studied before and after 10 min of repetitive isometric or isotonic tetanic contractions induced by electrical stimulation of the sciatic nerve (200-ms trains, 50 impulses/s, 1 contraction/s). F-V relationships and maximal velocity of shortening (Vmax) were determined by curve fitting with the Hill equation. Mean Vmax before fatigue was 3.8 +/- 0.2 (SE) average fiber lengths/s; mean maximal isometric tension (Po) was 508 +/- 15 g/g. With a significant decrease of force development during isometric contractions (-27 +/- 4%, P < 0.01, n = 5), Vmax was unchanged. However, with repetitive isotonic contractions at a low load (P/Po = 0.25, n = 5), a significant decrease in Vmax was observed (-21 +/- 2%, P < 0.01), whereas Po was unchanged. Isotonic contractions at an intermediate load (P/Po = 0.5, n = 4) resulted in significant decreases in both Vmax (-26 +/- 6%, P < 0.05) and Po (-12 +/- 2%, P < 0.01). These results show that repeated contractions of canine skeletal muscle produce specific changes in the F-V relationship that are dependent on the type of contractions being performed and indicate that decreases in other contractile properties, such as velocity development and shortening, can occur independently of changes in isometric tension.
Animals↗
[The inotropic and bathmotropic effects of beta stimulation: a study comparing dobutamine and dopamine on the guinea-pig papillary muscle in isotonic contraction].
The study was aimed at comparing the effects of dobutamine (dob) and dopamine (dop) on isotonic contraction and rhythmicity of isolated guinea-pig papillary muscles (in oxygenated Tyrode at 37 degrees C), by taking into account: 1) the rate of stimulation (50% above the diastolic threshold) at 5 fixed periods: (RR: 1600, 1200, 1000, 800 and 400 ms); 2) 7 log concentrations (logC) of the index amine (from 10(-9) to 10(-3) M). To this end, a dose-relation protocol which explored the effects of all 5 RR and 7 logC was designed and 15 adult female Guinea-pigs (250 to 350 g) were randomized to either the dob (n = 8) or the dop (n = 7) arm. This enabled a total of 525 sets of data to be analyzed: in 38 sets (7.2%) premature contractions (CP) were coded. CP were sustained (freq: > 3) in 25 of these latter 38 sets (4.8%). Compared to the basal state, the amplitude (AMP%) and the log of percent amplitude (logAMP%) and time to peak (TP%) changes of the isotonic (Gould transducer) twitch were calculated along with the log of this latter variable (logTP%). AMP%, log AMP%, TP% and logTP% were linearly correlated with logC at all RR. In the range 1600-400 RR, for both amines, significant linear correlations (magnitude of 0.15 > r < magnitude of 0.70, 0.001 > p < 0.022) were seen for plots of AMP%, logAMP% and TP%:steeper correlations were observed for dop. This was confirmed in multivariate analysis (BMDP-9R) whereby AMP%, logAMP%, TP%, logTP%, CP, and freqCP were dependent variables and coded variables were included to either define the type of treatment (dop versus dob) or logC. In these analyses, logC (t > 11) and dop (t > magnitude of 3) might be used to explain (0.28 > r2 < 0.42, 0.00001 > p < 0.0025) AMP% and logAMP%, meaning that a different inotropic (isotonic) efficacy exists between these 2 amines, at all logC. On the other hand, when CP and freqCP were coded, explanatory variables were AMP% and logAMP% (4.86 > t < 6.95, 0.06 > r2 < 0.09, p < 0.00001), but not the variable used to code the type of treatment (dob versus dop).(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Changes of tracheal smooth muscle stiffness during an isotonic contraction.
Stiffness of the series elastic component (SEC) of canine tracheal smooth muscle in isotonic contraction and relaxation was measured by applying small force perturbations to the muscle and measuring the resulting length perturbations. The quick, elastic length transient was taken as the change in length of the SEC (delta L). The force perturbation was a train of 10-Hz rectangular force waves varying from 0 to 10% maximum isometric tension (Po) in magnitude (delta P = 10% Po). Stiffness of the SEC was estimated by the ratio delta P/delta L. The change in SEC stiffness with respect to the change in muscle length was further studied by obtaining the stress-strain curves of the SEC at different muscle lengths using the load-clamping method. The clamps were applied at a fixed time (10 s after stimulation). Length of the muscle 10 s after contraction was controlled by the magnitude of the isotonic afterload. It was found that the apparent SEC stiffness increased as muscle length decreased. This stiffness increase is not likely due to an increase in the number of attached cross bridges, but it is probably due to the gradual diminution of the SEC length itself during muscle shortening.
Animals↗
Force-velocity relationship of human elbow flexors in voluntary isotonic contraction under heavy loads.
The force-velocity relationships of the human elbow flexors as one muscle in maximal voluntary contraction were determined using isotonic lever systems for seven men (19-38 yrs). The external loads used for the contraction weighed 0%, 20%, 40% 60%, 80% and 90% of maximum voluntary isometric force (Fo). The force and velocity were determined at an elbow angle of 90 degrees. The effect of the inertia of the forearm on the force was corrected using the angular acceleration of the forearm during an elbow flexion. The effect of muscular fatigue on the velocity during an elbow flexion was minimized by adjusting the initial elbow angle at the onset of the elbow flexion to the size of the load and reducing the time duration of the elbow flexion with a heavy load. Hill equation fitted fairly well to the force-velocity data observed in the experiments up to 90% Fo. The maximum isometric force predicted using Hill equation was larger by 6% (mean) than that observed in the experiments.
Adult↗
[Muscles as a chain of the Hill three element model for calculating asynchronicity of excitation in assessing the "active state" during isotonic contraction].
The muscle is described by the chain of Hill three-element models. The expression is obtained of the index of chemical energy transformation into the mechanical one ("active state") as a function of the velocity of the excitation wave propagation along the chain under isotonic contraction.
Mathematics↗
Agonist-induced isotonic contraction of cultured mesangial cells after multiple passage.
Contractile cells under conditions of prolonged culture lose their ability to contract in the usual manner (i.e., isotonically). One explanation for this may be that contraction is prevented by tight cell-to-substrate adhesion. Two models in which substrate adhesiveness was expected to be diminished were used to test this hypothesis. In one, cells were seeded onto collagen-coated dishes and used within 40 min of plating. In the other, cells were plated onto dishes coated with poly-2-hydroxyethyl methacrylate (poly-HEMA) and used, depending on thickness of the poly-HEMA substrate, up to periods of 1 wk. Cells plated onto such substrates contracted when challenged with either PGE2 (2 X 10(-6) and 2 X 10(-9) M), arginine vasopressin (AVP, 10(-6)-10(-9) ), or the calcium ionophore A23187 (5 micrograms/ml). Contraction took place within 5-15 min at 37 degrees C. The contraction seen with AVP was due to its pressor action because 1-desamino-8-D-arginine vasopressin (dDAVP), the antidiuretic analogue, did not cause contraction and the anti-pressor analogue [1-(beta-mercapto-beta beta-cyclopentamethylene propionic acid)-4-valine 8-D-arginine]-vasopressin [d(CH2)5-VDAVP] blocked contraction by AVP. The contraction seen with AVP was dependent on extracellular calcium, whereas that observed with prostaglandin E2 (PGE2) was not.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Modulation of cutaneous cortical evoked potentials during isometric and isotonic contractions in the monkey.
The effects of the direction of movement (flexion vs extension) and the nature of the motor task (isotonic vs isometric) on the modulation of sensory cortical evoked responses to cutaneous stimulation were investigated in one monkey. Sensory responses were assessed by measuring the magnitude of the short latency component of air puff-evoked potentials recorded intracortically in the arm representation of areas 3b and 1 in the primary somatosensory cortex. At most recording sites, it was found that the amplitude of the air puff-evoked potential was decreased in a non-specific manner by motor activity. Neither the timing nor the depth of the modulation were found to vary with either the direction or the type of contraction. The effects were widespread since inputs from practically the entire forelimb (hairy skin) were diminished during the motor tasks. These results thus show that the modulation was more closely linked to the central motor output than to the peripheral input generated by muscle force and/or limb displacement. It is suggested that signals originating from central motor structures, acting in a feedforward manner, play a major role in 'gating' cutaneous inputs during movement. It is further suggested that the centrally mediated effects are exerted via a final common pathway upon which the 'gating' signals converge.
Animals↗
Isometric and isotonic contractions in airway smooth muscle.
Canine tracheal smooth muscle was used as an in vitro model of smooth muscle in intrapulmonary airways to determine whether active tension curves derived from isometric and isotonic muscles are similar, and thus resemble striated muscle in this respect. Isometric, isotonic after-loaded, and isotonic free-loaded contractions elicited at different lengths and loads, were analysed. The data demonstrate that length-tension (L-T) diagrams were different in these various types of contractions for electrically and carbachol driven tracheal smooth muscles strips. In general, at any given length active tension is less in isotonic and free-loaded modes of contraction as compared with isometric. We conclude that the ability to actively develop tension at a given length in airway smooth muscle depends on the mode of contraction.
Animals↗
[Proceedings: Comparison between isometric and isotonic contraction of the guinea pig taenia coli (on a catch state)].
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