Contractile properties of the human triceps surae muscle during simulated weightlessness

The effect of a 120-day period of bed rest on the mechanical properties of human triceps surae muscle was studied in a group of male volunteers (n = 6, mean age 38 years). The results shows that the contractile properties of skeletal muscle in response to disuse change considerably. Time to isometric peak tension of the triceps surae muscle increased from 120 (SEM 3.0) ms to 136 (SEM 2.9) ms (P < 0.01), half relaxation time from 92 (SEM 2.1) ms to 100 (SEM 1.6) ms (P < 0.05) and total contraction time from 440 (SEM 9.9) ms to 540 (SEM 18.7) ms (P < 0.001). Isometric twitch force (F _t) decreased by a mean of 36.7% (P < 0.05), maximal voluntary contraction (MVC) and maximal force (F _max) by a mean of 45.5% and 33.7%, respectively (P < 0.05-0.01). The valueF _max:F _t ratio increased by 3.6% (nonsignificant). The difference betweenF _max and MVC, expressed as a percentage ofF _max and referred to as force deficiency, has also been calculated. Force deficit increased by a mean of 60% (P < 0.001) after bed rest. Force-velocity properties of the triceps surae muscle calculated according to an absolute scale of voluntary and electrically evoked contraction development decreased considerably. The calculations of the same properties on a relative scale did not differ substantially from the initial physiological state. The results would suggest that muscle disuse is associated with both atrophy and a reduction in contractility in the development ofF _max and decreased central (motor) drive. The change in the triceps surae muscle contractile velocity properties may indicate changes in the kinetically active state in the muscles.     

Physiological properties of human diaphragm muscle fibres and the effect of chronic obstructive pulmonary disease

The contractile and actomyosin ATPase properties of single fibres were examined in human diaphragm muscle obtained from patients with and without chronic obstructive pulmonary disease (COPD). Costal diaphragm biopsies were taken from five patients without evidence of COPD and from 11 age-matched individuals with varying degrees of the disease. Our aim was to establish whether changes in contractile properties of COPD diaphragm could be fully explained by the previously documented shift towards a greater proportion of type I myosin heavy chain isoform in COPD. The relative proportion of type I diaphragm fibres from non-COPD and COPD patients was measured by gel electrophoresis, and was negatively correlated with FEV(1) over the full range of values investigated. There was also significant atrophy of the type I fibre population in COPD diaphragms. Isometric tension was similar among the fibre types and between the COPD and non-COPD patients. The intrinsic energetic properties of diaphragm fibres were examined by monitoring the time-resolved actomyosin ATPase activity in COPD and non-COPD fibres that produced similar isometric forces. The isometric ATPase rate in COPD fibres was reduced to 50% of the rate in non-COPD fibres; hence, the cost of isometric contraction in type I and type IIA COPD fibres was reduced to between one-third and one-half of the tension cost calculated for non-COPD fibres. The rate of force development in type I COPD fibres was reduced to 50% of the rate seen in non-COPD type-I fibres. No difference in the rate of ATP consumption between COPD and non-COPD fibres was evident during isovelocity shortening. These data extend previous findings showing that aspects of breathing mechanics during progressive COPD are associated with remodelling of the diaphragm fibre-type distribution; on top of the increase in type I fibres there are fibre-specific reductions in force development rate (type I fibres) and ATPase rate that are consistent with the impairment of cross-bridge cycling kinetics.     

Contractile properties and histochemical characteristics of the rat diaphragm after prolonged triamcinolone treatment and nutritional deprivation

The influence of decreased muscle mass and reduced food intake on diaphragm structure and contractility in male Wistar rats was determined after triamcinolone acetate treatment (TR: 0.5mg per kg per day for 4 weeks) and two degrees of undernutrition (PW: pair-weight, which resulted in a similar (41%) reduction of body weight as TR; PF: pair-fed, which resulted in a moderate (13%) reduction of body weight) and a free-fed control group (FF, with an increase (9%) in body weight). Energy intake of TR decreased, but based on daily measurements of food intake and body weight, energy expenditure of the TR rats was increased compared with the other groups. Body (BW) and muscle weights were reduced in proportion to the extent of undernutrition in the nutritionally deprived rats (i.e. BW and diaphragm weight of PF animals were reduced 21% and 16% respectively compared with FF, v. a 48% and 41% reduction in the PW group). Triamcinolone-induced atrophy was limited to type II fibres (30% of type IIa and 45% of type IIx/b, p<0.05), while severe chronic undernutrition (PW) induced a generalized fibre type atrophy in the diaphragm (23% type I, 38% type IIa and 49% type IIx/b, p<0.05), and moderate undernutrition (PF) caused only significant type IIa atrophy (20%, p<0.05). A leftward shift of the diaphragmatic tension–frequency relationship and a decreased fatiguability of the TR and PW bundles were observed (p<0.01), while the PF bundles were not significantly different compared with FF. These results suggest that triamcinolone and severe undernutrition cause similar alterations in in vitro contractility of the diaphragm. The effects of triamcinolone treatment on diaphragm structure may be partly explained by the reduced food intake, but the atrophy pattern induced by severe undernutrition (PW) was different. This revised version was published online in July 2006 with corrections to the Cover Date.     

Contractile properties of human skeletal muscle in childhood and adolescence

Summary Using a combination of single maximal stimuli and maximum voluntary contractions, a comparison has been made of muscle properties in pre- and post-pubertal male subjects. In the dorsiflexor and plantarflexor muscles of the ankle, the twitch and maximum voluntary torques were approximately twice as large in the older subjects; the mean height and mean weight increased by factors of 1.20 and 1.86 respectively. The only other muscle parameter that changed, as a function of age, was the contraction time of the ankle dorsiflexors; the mean value was significantly longer in the older subjects. In the younger subjects, there were already clear differences between the dorsiflexor and plantarflexor muscles, the former developing smaller torques and having shorter contraction and half-relaxation times, greater post-activation potentiation and more susceptibility to fatigue. Even in the youngest subject, motor unit activation was complete in the ankle dorsiflexors; although this was not always true of the plantarflexors, the difference between the two subject groups was not significant.Supported by the Muscular Dystrophy Association of Canada     

Contractile properties of the human triceps surae following prolonged exercise and beta-blockade

Sixteen healthy males volunteered to perform both an incremental maximal and prolonged submaximal treadmill test with beta-blockade (2 X 80 mg oral propranolol per day) or matched placebo in a blind crossover design. Prior to and following the prolonged exercise, electrical stimulation of the triceps surae was performed to examine contractile properties. During the maximal test, the heart rate (HR) was reduced at all times by beta-blockade. The time to exhaustion in this test was significantly reduced by beta-blockade (P less than 0.03), while the maximal oxygen uptake (VO2 max) was not significantly lower (P = 0.06). In response to prolonged treadmill walking at 60% of VO2 max, the HR was reduced but VO2, respiratory quotient and ventilation were not affected by beta-blockade relative to placebo. Plasma concentrations of free fatty acids increased during exercise in the placebo but not beta-blocked treatment (P less than 0.0001). Plasma noradrenalin and adrenalin increased with exercise; the increase in adrenalin with beta-blockade was greater than that with placebo (P less than 0.0001). The RPE obtained at intervals during the prolonged exercise were greater for beta-blockades than placebo. Eight of 16 subjects were unable to complete full 90 min with beta-blockade; but all 16 completed the test with placebo. The electrically evoked twitches in the triceps surae muscle group after exercise did not differ in peak torque or one-half relaxation time compared to pre-exercise. The time to peak twitch torque was significantly shorter after exercise. No differences in twitch were observed due to beta-blockade. The tetanic responses at 10, 20, 50 and 100 Hz were not affected by either exercise or the beta-blockade. In conclusion, an increased subjective estimate of fatigue (RPE) was observed during prolonged exercise with beta-blockade. This subjective fatigue did not relate to altered peripheral muscle force production during electrical stimulation. The results suggest either a central rather than peripheral origin of fatigue, or fatigue in a muscle group not examined by stimulation of the triceps surae.     

Contractile events during inflammation

Contractile events during wound healing.During granulation tissue contraction, fibroblasts develop characteristics typical of smooth muscle: (1) they contain an extensive cytoplasmic fibrillar system, (2) they show immunofluorescent labeling of anti-actin antibodies, (3) there are cell to cell and cell to stroma attachments, (4) strips of granulation tissue, when tested pharmacologically in vitro, behave similarly to smooth muscle.These data support the view that under certain conditions, fibroblasts can differentiate into a cell type structurally and functionally similar to smooth muscle and this cell, the myofibroblast, plays an important role in connective tissue contraction.During epithelialization, epidermal cells develop an extensive cytoplasmic contractile apparatus which has morphological and immunological characteristics similar to those of myofibroblasts. Such apparatus disappears as soon as epithelialization is completed. It is proposed that such a contractile apparatus plays a role in cell motility enabeling individual cells to rearrange themselves in an appropriate pattern.In conclusion, significant amounts of contractile proteins may be synthetized by fibroblasts and epithelial cells during wound healing and may play an important role in this process.     

Contractile properties of smooth-muscle cells of the aorta during the development of experimental a therosclerosis

Contractile responses of smooth-muscle cells to the action of catecholamines and KCl at 27 and 37°C, under normal conditions and in the initial stages of atherosclerosis, were investigated in experiments on isolated ring segments of the rabbit aorta. The contractile responses of the atherosclerotic aorta induced by KCl were of lower amplitude than in the intact aorta, but the opposite pattern was found after the action of catecholamines. Lowering the temperature depresses the contractile responses of both the normal and the atherosclerotic aorta.Department of Normal Physiology, Leningrad Sanitary-Hygiene Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR, V. V. Zakusov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 82, No. 9, pp. 1036–1038, September, 1976.     

Contractile properties during development of hypertrophy of the smooth muscle in the rat portal vein

Structural and mechanical alterations during hypertrophy of the rat portal vein were investigated. Growth of the vessel was induced by a partial ligature of the vessel causing an increased transmural pressure. Vessel segments from animals kept with ligature for 1, 3, 5 and 7 days, were compared with vessels from sham-operated animals. Maximal active force and vessel cross-sectional area increased with time in the ligated group. On day 7, force and cross-sectional area at the optimal length, were markedly increased in the ligated group (21.1 +/- 1.0 mN, 0.55 +/- 0.04 mm2, n = 9) compared with the control vessels (11.7 +/- 1.0 mN, 0.30 +/- 0.02 mm2, n = 7). Light and electron microscopy of preparations fixed at optimal length showed that the amount of smooth muscle and the cross-sectional area of cell profiles were almost doubled in the ligated group on day 7, consistent with hypertrophy of the smooth muscle. The force per smooth muscle cell area was similar in the two groups (ligated: 132 +/- 15; control: 145 +/- 16 mN mm-2, n = 4-5). The maximal shortening velocity was significantly lower in the hypertrophied group (ligated: 0.28 +/- 0.02; control: 0.41 +/- 0.01 optimal length s-1, n = 6). In chemically skinned preparations, activated by maximal thiophosphorylation of the myosin light chains, force was higher in the ligated group compared to the controls but no difference in maximal shortening velocity was observed. In conclusion, the increased transmural pressure is associated with a rapid increase in the amount of smooth muscle in the portal vein. The mechanical data show that after 7 days the force generating ability of the contractile system has increased in proportion to the smooth muscle cell mass. The unaltered maximal shortening velocity in the skinned hypertrophied preparations suggests that the kinetic properties of the maximally activated contractile system are unaltered. The decreased maximal shortening velocity in the intact hypertrophied preparations may reflect alterations in the excitation-contraction coupling.     

Contractile properties of the human tibialis anterior muscle at different stages of denervation and reinnervation

Department of Normal Physiology and Department of Nervous Diseases Medical Institute, Kazan'. (Presented by Academician of the Academy of Medical Sciences of the USSR A. D. Ado.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 106, No. 10, pp. 395–397, October, 1988.     

Contractile properties of isolated muscle spindles of the frog

Force and isotonic shortening velocities were studied (0.6-4.0 °C) in isolated single muscle spindles from the anterior tibialis muscle of Rana temporaria using techniques that enabled measurements both from the spindle as a whole and from marked segments of the preparation. The force-velocity relationship during tetanic stimulation exhibited the same biphasic shape as previously described for extrafusal muscle fibres. However, the maximum speed of shortening of the spindle fibres was merely 0.95 ± 0.006 lengths s⁻¹ (mean ± s.e.m. ,   n = 11  ), which is approximately half the value recorded in extrafusal fibres of the same muscle. The maximum tetanic force, 91 ± 10 kN m⁻²,   n = 14  , was likewise only approximately half that produced by extrafusal fibres. The force generated by the capsule segment was lower than that produced by the whole spindle resulting in elongation of the capsule region during a fixed-end tetanus. The intracellular calcium ion concentration reached during the plateau of the tetanus, 1.7 ± 0.1 μM (   n = 8  ), was substantially lower than the value attained in extrafusal fibres under equivalent conditions. In accordance, the spindle fibres did not become fully activated during supramaximal electrical stimulation as indicated by the finding that the tetanic force could be further increased by 16.6 ± 0.04 % (   n = 5  ) on addition of 0.5 m m caffeine. Inadequate activation may thus, to a certain extent, account for the relatively low force per cross-sectional area of the spindle fibres. The contractile properties of the intrafusal fibres should make the spindle organ suited to provide feedback control during eccentric (forced lengthening) and static (isometric) contractions and, with reduced effectiveness, during slow muscle shortening.     

Contractile properties of the human triceps surae with some observations on the effects of temperature and exercise

Summary The contractile properties of the triceps of five healthy male subjects (mean age 22 years) during electrically stimulated and voluntary isometric muscle contractions were investigated and some observations made on the effects of muscle heating and cooling and dynamic exercise. The times to peak twitch tension (TPT) and half relaxation time (1/2RT) were 111±20 ms and 83±13 ms respectively. Heating and prior exercise decreased, and cooling severely prolonged, TPT and 1/2RT. Exercise and heating had no effect on supramaximal twitch tension (P_t0) but cooling the muscle to a temperature of 24.3‡ C reduced it by 52%. The effects of repetitive stimuli on P_t0 were dependent on frequency; at 0.2 Hz potentiation was observed but at 2 Hz, P_t0 was depressed under control conditions. Heating had no effect on these responses but cooling reversed the 2 Hz and abolished 0.2 Hz response. Post-tetanic potentiation of the twitch was observed under all conditions of measurement. At submaximal stimulation voltages, heating and exercise enhanced twitch and tetanic tensions, but at supramaximal voltages heating reduced tetanic tension (P₀) at 10 Hz (by 115N), though not at 20 Hz. Exercise decreased P₀ at both frequencies of stimulation. Cooling significantly reduced the maximal voluntary contraction and P₀ at 20 Hz. At submaximal voltages, heating enhanced and cooling severely depressed tetanic tensions at high frequency (100 Hz) stimulation. A 2-min fatigue test was unaffected by heating but cooling reduced force generation at the onset of, and the decline of force during, the test. It was concluded that studies of the contractile properties of human muscle in vivo should be based on supramaximal stimulation, and that temperature and prior exercise should be carefully standardised in order to obtain reliable and meaningful results.     

Size and location of the fetal diaphragm during the fetal period in human fetuses

Aim The aim of this study was to determine the development and the size and localization of the diaphragm during the fetal period in human fetuses. Materials and methods One hundred and eighty-four diaphragm obtained from human fetuses aged between 9 and 40 weeks of gestation was used in this study. The localization of the diaphragm with respect to abdominal cavity and the level of costodiaphragmatic recess with respect to the ribs were determined. The dimensions (height, width, and depth) of the diaphragm were measured. The diameter and localization of apertures on the diaphragm were determined. Results During the fetal period, the costodiaphragmatic recess was most commonly located at the level of the 9th rib. Means and standard deviations of the all parameters with respect to gestational weeks and months were calculated. No significant differences were observed between sexes for any of the parameters (P > 0.05). All parameters were increasing with age during fetal period. There was significant correlation between gestational age and all parameters (P < 0.001). The localizations of the diaphragmatic apertures did not change throughout the fetal period and aortic hiatus and oesophageal hiatus were most frequently situated to the left of the median plane. Conclusion New data are derived for human fetuses to evaluate diaphragmatic development. Data acquired in this study are believed to contribute to studies of obstetrics, perinatology, forensic medicine and fetal pathology on fetal development of the diaphragm, and diagnosis of its anomalies, pathologies and variations.     

Contractile activity of lymphatic microvessels during the febrile reaction

Department of Pathology with Pharmacotherapy Course, S. V. Kuzashov Kazan' Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR A. D. Ado.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 110, No. 9, pp. 328–330, September, 1990.     

Role of nitric oxide in isometric contraction properties of rat diaphragm during hypoxia

Hypoxia disturbs Ca²⁺ regulation and increases the intracellular Ca²⁺ concentration ([Ca²⁺]_i), which may in turn activate the nitric oxide synthase (NOS) regulated by [Ca²⁺]_i. Since nitric oxide (NO) reduces the isometric contractility of rat diaphragm in vitro, we hypothesized that NO contributes to the impaired force generation of an hypoxic diaphragm. The effects of different concentrations of the NOS inhibitor, N^G-monomethyl-L-arginine (L-NMMA), the NO scavenger haemoglobin (150 μmol·l^–1) and the NO donor spermine NONOate (Sp-NO; 1 mmol·l^–1) were determined on isometric contractility during hypoxia [partial pressure of oxygen, PO₂, about 7 kPa (about 54 mmHg)] and hyperoxia [PO₂ about 83 kPa (about 639 mmHg)]. Hypoxia significantly reduced maximal twitch force (F _t), and submaximal tetanic force (30 Hz, F ₃₀) in all L-NMMA groups. A low concentration of L-NMMA (30 μmol·l^–1) increased F ₃₀ but a high concentration (1,000 μmol·l^–1) reduced F ₃₀ during hypoxia. The effects of L-NMMA on force generation were more pronounced during hypoxia compared to hyperoxia. Peak increases in F ₃₀ and F _t were observed at a concentration of 30 μmol·l^–1 L-NMMA during hypoxia, but with 10 μmol·l^–1 L-NMMA during hyperoxia. The same concentration of haemoglobin increased F ₃₀ and F _t less during hypoxia compared to hyperoxia. The Sp-NO reduced F _t, F ₃₀ and maximal tetanic force (F ₀) during hypoxia; these effects were abolished in the presence of haemoglobin. The Sp-NO did not alter F _t, F ₃₀ and F ₀ during hyperoxia. We conclude that NO plays a more prominent role during hypoxia and that NO contributes to the depression of force generation in the hypoxic rat diaphragm in vitro. This change may be related to an elevated NO generation within the hypoxic diaphragm. Electronic Publication