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Contractile Properties (contractile + property)

Distribution by Scientific Domains

Life Sciences	53%
Medical Sciences	39%
2 Other Domains	8%

Selected Abstracts

Surface Action Potential and Contractile Properties of the Human Triceps Surae Muscle: Effect of ,Dry' Water Immersion

EXPERIMENTAL PHYSIOLOGY, Issue 1 2002
Yuri A. Koryak
The effects of 7 days of ,dry' water immersion were investigated in six subjects. Changes in the contraction properties were studied in the triceps surae muscle. After immersion, the maximal voluntary contraction (MVC) was reduced by 18.9% (P < 0.01), and the electrically evoked (150 impulses s,1) maximal tension during tetanic contraction (Po) was reduced by 8.2% (P > 0.05). The difference between Po and MVC expressed as a percentage of Po and referred to as force deficiency was also calculated. The force deficiency increased by 44.1% (P < 0.001) after immersion. The decrease in Po was associated with increased maximal rates of tension development (7.2%) and relaxation. The twitch time-to-peak was not significantly changed, and half-relaxation and total contraction time were decreased by 5.3% and 2.8%, respectively, but the twitch tension (Pt) was not significantly changed and the Pt/Po ratio was decreased by 8.7%. The 60 s intermittent contractions (50 impulses s,1) decreased tetanic force to 57% (P < 0.05) of initial values, but force reduction was not significantly different in the two fatigue-inducing tests: fatigue index (the mean loss of force of the last five contractions, expressed as a percentage of the mean value of the first five contractions) was 36.2 ± 5.4% vs. 38.6 ± 2.8%, respectively (P > 0.05). While identical force reduction was present in the two fatigue-inducing tests, it would appear that concomitant electrical failure was considerably different. Comparison of the electrical and mechanical alterations recorded during voluntary contractions, and in contractions evoked by electrical stimulation of the motor nerve, suggests that immersion not only modifies the peripheral processes associated with contraction, but also changes central and/or neural command of the contraction. At peripheral sites, it is proposed that the intracellular processes of contraction play a role in the contractile impairment recorded during immersion. [source]

Contractile Properties, Fatigue and Recovery are not Influenced by Short-Term Creatine Supplementation in Human Muscle

EXPERIMENTAL PHYSIOLOGY, Issue 4 2000
J. M. Jakobi
There have been several studies on the effect of short-term creatine (Cr) supplementation on exercise performance, but none have investigated both voluntary and stimulated muscle contractions in the same experiment. Fourteen moderately active young men (19-28 years) were randomly assigned, in a double blind manner, to either a creatine (Cr) or placebo (P) group. The subjects supplemented their regular diet 4 times a day for 5 days with either 5 g Cr + 5 g maltodextrin (Cr group), or 5 g maltodextrin (P group). Isometric maximal voluntary contraction (MVC), muscle activation, as assessed using the modified twitch interpolation technique, electrically stimulated contractile properties, electromyography (EMG), endurance time and recovery from fatigue were measured in the elbow flexors. The fatigue protocol involved both voluntary and stimulated contractions. Following supplementation there was a significant weight gain in the Cr group (1.0 kg), whereas the P group did not change. For each group, pre-supplementation measures were not significantly different from post-supplementation for MVC, twitch and tetanic tensions at rest, time to peak tension, half-relaxation time and contraction duration. Prior to Cr supplementation time to fatigue was 10 ± 4 min (mean ± S.E.M.) for both groups, and following supplementation there was a non-significant increase of 1 min in each group. MVC force, muscle activation, EMG, stimulated tensions and durations were similar for the Cr and P groups over the course of the fatigue protocol and did not change after supplementation. Furthermore, recovery of MVC, stimulated tensions and contractile speeds did not differ as a result of Cr supplementation. These results indicate that short-term Cr supplementation does not influence isometric elbow flexion force, muscle activation, stimulated contractile properties, or delay time to fatigue or improve recovery. [source]

Force,frequency and force,length properties in skeletal muscle following unilateral focal ischaemic insult in a rat model

ACTA PHYSIOLOGICA, Issue 3 2009
G. N. Dormer
Abstract Aim:, Our purpose was to quantify skeletal muscle properties following unilateral focal ischaemic insult (stroke) in a rat model. Methods:, Male rats were divided into two groups: stroke and 2 weeks recovery (n = 8) and control group (n = 7). Stroke was induced in the area of the motor neocortex containing hind limb corticospinal neurones. Contractile properties of the medial gastrocnemius muscle were measured in situ in both limbs. Force,length and force,frequency properties were measured before and 35 min after 5 min fatiguing stimulation. Results:, Stroke resulted in bilateral tetanic fade during 200 Hz stimulation. When normalized to 100 Hz contractions, force at 200 Hz was 95.4 ± 0.9% for the paretic muscles, 96.7 ± 1.7% for non-paretic muscles and 102.2 ± 1.0% for muscles of control rats (P = 0.006). Prior to fatiguing contractions, there was no difference in the length dependence of force. During repetitive contractions, active force fell significantly to 19 ± 4 and 25 ± 5% of initial force in paretic and non-paretic muscles of animals with a stroke respectively. In control animals active force fell to 37 ± 5%. During repetitive contractions, fusion index increased in muscles of stroke animals to 1.0 ± 0 but in control animals it was 0.95 ± 0.02. There was selective force depression at short lengths for fatigued paretic muscle (significant difference at muscle lengths less than reference length ,2 mm). Conclusion:, The tetanic fade at high stimulation frequencies indicates that there may be activation failure following focal ischaemic insult. The greater magnitude of fatigue and selective depression at short lengths following repetitive contractions should be investigated further. [source]

Influence of Genetically Predisposed Diabetes on Ethanol-Induced Depression of Cardiac Contraction in Adult Rat Ventricular Myocytes

EXPERIMENTAL PHYSIOLOGY, Issue 3 2002
Jun Ren
Diabetes mellitus and alcohol (ethanol) intake are two positively correlated major risk factors for cardiovascular abnormalities. However, the interaction of the two on cardiac function is largely unknown. The purpose of the present study was to examine the impact of genetically predisposed diabetes on acute ethanol exposure-induced cardiac contractile depression at the myocyte level. Ventricular myocytes from spontaneously biobreeding diabetes-prone (BBDP) rats and their diabetes-resistant littermates (BBDR) were stimulated to contract at 0.5 Hz. Contractile properties analysed include: peak shortening amplitude (PS), time-to-PS (TPS), time-to-90% relengthening (TR90) and maximal velocities of shortening/relengthening (± dL/dt). BBDP rats displayed hyperglycaemia, reduced body weight gain and increased cardiac, hepatic and renal size. Myocytes isolated from BBDP rat hearts exhibited prolonged TPS and TR90 associated with normal PS and ± dL/dt, compared with myocytes from the BBDR group. Acute ethanol exposure (80-640 mg dl,1) caused a concentration-dependent inhibition of PS in both BBDR and BBDP myocytes. However, the degree of inhibition of PS was significantly reduced in BBDP myocytes compared to that of BBDR myocytes. The maximal inhibition was 52.9% and 28.4% in BBDR and BBDP groups, respectively. Ethanol significantly depressed ± dL/dt in both BBDR and BBDP myocytes. In addition, ethanol did not affect TPS or TR90 in either the BBDR or BBDP group. Collectively, these results suggest that the ethanol-induced depression in cardiac myocyte contraction may be ,shadowed' by genetically predisposed diabetes. [source]

Iso-S -petasin, a hypotensive sesquiterpene from Petasites formosanus, depresses cardiac contraction and intracellular Ca2+ transients in adult rat ventricular myocytes

JOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 1 2003
Lucy B. Esberg
ABSTRACT Petasites formosanus is an indigenous species of the medicinal plant Petasites which has been used to treat hypertension. Both S -petasin and its isoform iso-S -petasin have been shown to be the effective ingredients in P. formosanus. However, their effect on heart function has not been revealed. This study was to examine the effect of iso-S -petasin on cardiac contractile function at the myocyte level. Ventricular myocytes were isolated from adult rat hearts and were stimulated to contract at 0.5 Hz under 1.0 mm extracellular Ca2+. Contractile properties were evaluated using an lonOptix MyoCam system including peak shortening (PS), time to PS (TPS), time to 90% re-lengthening (TR90) and maximal velocity of shortening/re-lengthening (±dL/dt). Intracellular Ca2+ properties were assessed by fura-2 and presented as Ca2+ -induced Ca2+ release (CICR) and intracellular Ca2+ decay. Acute application of iso-S -petasin (10,7 to 10,4 M) elicited a concentration-dependent inhibition in PS and CICR, with maximal inhibitions of 51.0% and 31.0%, respectively. iso-S -petasin also induced a concentration-dependent inhibition of ± dL/dt without affecting TPS, TR90, baseline intracellular Ca2+ level or intracellular Ca2+ decay. Elevation of extracellular Ca2+ from 1.0 mm to 2.7 mm significantly antagonized the iso-S -petasin-induced depression in PS and CICR. These results demonstrated a direct depressant action of iso-S -petasin on ventricular contraction, which may work in concert with its antihypertensive action to reduce the cardiac load. The iso-S -petasin-induced decrease in CICR may play a role in its cardiac depressant effect. [source]

Contractile properties of human motor units in health, aging, and disease

MUSCLE AND NERVE, Issue 9 2001
FRCPC, K. Ming Chan MD
Abstract The primary function of skeletal muscle is to produce force for postural control and movement. Although the contractile properties of the whole muscle are useful functional indicators, they do not accurately reflect the heterogeneity of the constituent motor units (MUs) and their changes in health and disease. However, data on the contractile properties of human MUs, in comparison to other animal species, are relatively sparse. This, in part, is due to greater methodological challenges of in vivo studies of MUs in the human. The purpose of this review is to critically appraise the methods used in humans; to describe the normative data from different muscle groups; to discuss differences between data from healthy humans and other animal species; and, last, to characterize changes of the MU contractile properties in aging, disease, and in response to intervention. Because the spike-triggered averaging technique can only be used to study the twitch properties, other methods were subsequently developed to measure a wider range of contractile properties. Although there is general agreement between human data and those from other animal species, major differences do exist. Potential reasons for these discrepancies include true biological differences, but differences in the techniques used may also be responsible. Although limited, measurement of MU contractile properties in humans has provided insight into the changes associated with aging and motoneuronal diseases and provides a means of gauging their adaptive capacity for training and immobilization. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 1113,1133 [source]

Contractile properties of the proximal urethra and bladder in female pig: Morphology and function

NEUROUROLOGY AND URODYNAMICS, Issue 1 2006
J.J.M. Pel
Abstract Aims To compare the contractile properties of proximal urethral and bladder muscle of the female pig. Materials and Methods In two proximal segments (I and II) of the urethra, small muscle bundles were excised to measure the force-length (maximum force) and the force-velocity (unloaded shortening velocity) relation using the stop-test. The rate of force development was calculated using phase plots. Contractile properties of urethral and bladder segments were statistically compared using the Mann,Whitney U -test. Immunohistochemical staining of whole circumference urethral cross sections was used to identify the location of smooth and striated muscle fibres. Results On isometric force development, the urethral muscle bundles revealed a fast (,0.5 sec) and a slow (,2.1 sec) time constant, whereas in bladder only a slow (,2.3 sec) component was measured. On average, isometric force was highest in bladder. The length range over which force was produced was smallest in urethral segment II, followed by urethral segment I and finally bladder. The unloaded shortening velocity was 0.15, 0.25 and 0.35 1/sec, respectively. Histological preparations showed that smooth as well as striated muscle was present in proximal urethra. In urethral muscle bundles, spontaneous contractions were measured with a frequency of 0.4 Hz. Conclusions Differences in contractility found between urethra and bladder may be ascribed to the presence of striated muscle in the proximal urethra. The regulation of tone and spontaneous contractions may be part of the continence mechanism in the female pig urinary tract. © 2005 Wiley-Liss, Inc. [source]

Differential age-related changes in motor unit properties between elbow flexors and extensors

ACTA PHYSIOLOGICA, Issue 1 2010
B. H. Dalton
Abstract Aim:, Healthy adult ageing of the human neuromuscular system is comprised of changes that include atrophy, weakness and slowed movements with reduced spinal motor neurone output expressed by lower motor unit discharge rates (MUDRs). The latter observation has been obtained mostly from hand and lower limb muscles. The purpose was to determine the extent to which elbow flexor and extensor contractile properties, and MUDRs in six old (83 ± 4 years) and six young (24 ± 1 years) men were affected by age, and whether any adaptations were similar for both muscle groups. Methods:, Maximal isometric voluntary contraction (MVC), voluntary activation, twitch contractile properties, force,frequency relationship and MUDRs from sub-maximal to maximal intensities were assessed in the elbow flexors and extensors. Results:, Both flexor and extensor MVCs were significantly (P < 0.05) less (,42% and ,46% respectively) in the old than in the young. Contractile speeds and the force,frequency relationship did not show any age-related differences (P > 0.05). For the elbow flexors contraction duration was ,139 ms and for the extensors it was ,127 ms for both age groups (P > 0.05). The mean MUDRs from 25% MVC to maximum were lower (,10% to ,36%) in the old than in the young (P < 0.01). These age-related differences were larger for biceps (Cohen's d = 8.25) than triceps (Cohen's d = 4.79) brachii. Conclusion:, Thus, at least for proximal upper limb muscles, mean maximal MUDR reductions with healthy adult ageing are muscle specific and not strongly related to contractile speed. [source]

Changes in the contractile properties of motor units in the rat medial gastrocnemius muscle after one month of treadmill training

ACTA PHYSIOLOGICA, Issue 4 2008
M. Pogrzebna
Abstract Aim:, The influence of 4 weeks treadmill training on the contractile properties of motor units (MUs) in the rat medial gastrocnemius muscle was investigated. Methods:, A population of 18 Wistar rats was divided into two groups: trained on a treadmill (n = 7, locomotion speed 27 cm s,1, 1 km daily, 5 days a week, for 4 weeks) and control (n = 11). The contractile properties of isolated MUs were studied. Functional isolation of units was achieved by electrical stimulation of filaments of the ventral roots. A total of 299 MUs were investigated (142 in the control group and 157 in the trained group). They were divided into fast fatigable (FF), fast resistant to fatigue (FR) and slow (S). Their proportions and parameters of contractions were analysed. Results:, Following training, the number of FF units decreased and the number of FR units increased. The distribution of the fatigue index changed within these two types of fast units. The twitch and tetanus forces increased considerably in fast MUs, mainly in those of the FF type. The contraction and relaxation times shortened in the FR and S MUs. The steep part of the force,frequency curves shifted towards higher stimulation frequencies in FR and S units, while in FF units the shift was in the opposite direction. Conclusion:, The significant change in the proportions of fast MUs following training indicates FF to FR transformation. The various effects of training seen in the different MU types help explain the rationale behind mixed training. [source]

Contractility of single human dermal myofibroblasts and fibroblasts

CYTOSKELETON, Issue 2 2002
Louise K. Wrobel
Abstract Human dermal myofibroblasts, characterised by the expression of ,-smooth muscle actin, are part of the granulation tissue and implicated in the generation of contractile forces during normal wound healing and pathological contractures. We have compared the contractile properties of single human dermal fibroblasts and human dermal myofibroblasts by culturing them on flexible silicone elastomers. The flexibility of the silicone substratum permits the contractile forces exerted by the cells to be measured [Fray et al., 1998: Tissue Eng. 4:273,283], without changing their expression of ,-smooth muscle actin. The mean contractile force produced by myofibroblasts (2.2 ,N per cell) was not significantly different from that generated by fibroblasts (2.0 ,N per cell) when cultured on a substrata with a low elastomer stiffness. Forces produced by fibroblasts were unaffected by increases in elastomer stiffness, but forces measured for myofibroblasts increased to a mean value of 4.1 ,N/cell. This was associated with a higher proportion of myofibroblasts being able to produce wrinkles on elastomers of high stiffness compared to fibroblasts. We discuss the force measurements at the single cell level, for both fibroblast and myofibroblasts, in relation to the proposed role of myofibroblasts in wound healing and pathological contractures. Cell Motil. Cytoskeleton 52:82,90, 2002. © 2002 Wiley-Liss, Inc. [source]

Fibre-type composition of rabbit jaw muscles is related to their daily activity

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2005
T. van Wessel
Abstract Skeletal muscles contain a mixture of fibres with different contractile properties, such as maximum force, contraction velocity and fatigability. Muscles adapt to altered functional demands, for example, by changing their fibre-type composition. This fibre-type composition can be changed by the frequency, duration and presumably the intensity of activation. The aim of this study was to analyse the relationship between the spontaneous daily muscle activation and fibre-type composition in rabbit jaw muscles. Using radio-telemetry combined with electromyography, the daily activity of five jaw muscles was characterized in terms of the total duration of muscle activity (duty time) and the number of activity bursts. Fibre-type composition of the muscles was classified by analysing the myosin heavy chain content of the fibres. The amount of slow-type fibres was positively correlated to the duty time and the number of bursts only for activations exceeding 20,30% of the maximum activity per day. Furthermore, cross-sectional areas of the slow-type fibres were positively correlated to the duty time for activations exceeding 30% of the maximum activity. The present data indicate that the amount of activation above a threshold (> 30% peak activity) is important for determining the fibre-type composition and cross-sectional area of slow-type fibres of a muscle. Activation above this threshold occurred only around 2% of the time in the jaw muscles, suggesting that contractile properties of muscle fibres are maintained by a relatively small number of powerful contractions per day. [source]

Ovalbumin-induced sensitization affects non-quantal acetylcholine release from motor nerve terminals and alters contractility of skeletal muscles in mice

EXPERIMENTAL PHYSIOLOGY, Issue 2 2009
Alexander Y. Teplov
Skeletal muscles play key roles in the development of various pathologies, including bronchial asthma and several types of auto-immune disorders, e.g. polymyositis. Since most of these maladies have an immunological/allergic element, this paper is devoted to assessing the impact of immunobiological reorganization on the functional properties of isolated skeletal muscles in mice. A combination of two methods (myography and electrophysiology) was used to evaluate extensor digitorum longus (EDL) and diaphragmatic muscle (DM) in this regard. Conventional myographic technique showed that ovalbumin-induced sensitization (OS) produced different changes in the contractile properties of EDL and DM. The amplitudes of carbachol (CCh)-induced contractions increased in DM but decreased in EDL. Those changes were inversely related to OS-mediated changes of non-quantal acetylcholine (ACh) release intensity within the muscle endplate, as shown by the electrophysiologically measured H-effect. These results clearly show that OS-mediated changes of non-quantal ACh release alter the functional properties of postjunctional ACh receptors and therefore contribute to the disturbance of CCh-induced contractility of skeletal muscles. Other mechanisms of OS-mediated changes of skeletal muscle contractility are also proposed and discussed. [source]

Changes in contractile properties of motor units of the rat medial gastrocnemius muscle after spinal cord transection

EXPERIMENTAL PHYSIOLOGY, Issue 5 2006
Jan Celichowski
The effects of complete transection of the spinal cord at the level of Th9/10 on contractile properties of the motor units (MUs) in the rat medial gastrocnemius (MG) muscle were investigated. Our results indicate that 1 month after injury the contraction time (time-to-peak) and half-relaxation time were prolonged and the maximal tetanic force in most of the MUs in the MG muscle of spinal rats was reduced. The resistance to fatigue also decreased in most of the MUs in the MG of spinal animals. Moreover, the post-tetanic potentiation of twitches in MUs diminished after spinal cord transection. Criteria for the division of MUs into three types, namely slow (S), fast fatigue resistant (FR) and fast fatigable (FF), applied in intact animals, could not be directly used in spinal animals owing to changes in contractile properties of MUs. The ,sag' phenomenon observed in unfused tetani of fast units in intact animals essentially disappeared in spinal rats and it was only detected in few units, at low frequencies of stimulation only. Therefore, the MUs in spinal rats were classified as fast or slow on the basis of an adjusted borderline of 20 ms, instead of 18 ms as in intact animals, owing to a slightly longer contraction time of those fast motor units with the ,sag'. We conclude that all basic contractile properties of rat motor units in the medial gastrocnemius muscle are significantly changed 1 month after complete spinal cord transection, with the majority of motor units being more fatigable and slower than those of intact rats. [source]

Contractile Properties, Fatigue and Recovery are not Influenced by Short-Term Creatine Supplementation in Human Muscle

Undulatory fish swimming: from muscles to flow

FISH AND FISHERIES, Issue 2 2006
Ulrike K. Müller
Abstract Undulatory swimming is employed by many fish for routine swimming and extended sprints. In this biomechanical review, we address two questions: (i) how the fish's axial muscles power swimming; and (ii) how the fish's body and fins generate thrust. Fish have adapted the morphology of their axial musculature for high power output and efficiency. All but the superficial muscle fibres are arranged along curved trajectories, and the myomeres form nested cones. Two conflicting performance goals shape the fibre trajectories of the axial muscles. Maximum power output requires that all fibres contract uniformly. In a bending fish, uniform contraction in a single myomere can be ensured by curved fibre trajectories. However, uniform strain is only desirable if all muscle fibres have the same contractile properties. The fish needs several muscle-fibre types that generate maximum power at different contraction speeds to ensure effective muscle power generation across a range of swimming speeds. Consequently, these different muscle-fibre types are better served by non-uniform contractions. High power output at a range of swimming speeds requires that muscle fibres with the same contractile properties contract uniformly. The ensuing helical fibre trajectories require cone-shaped myomeres to reduce wasteful internal deformation of the entire muscle when it contracts. It can be shown that the cone-shaped myomeres of fish can be explained by two design criteria: uniform contraction (uniform strain hypothesis) and minimal internal deformation (mechanical stability hypothesis). So far, only the latter hypothesis has found strong support. The contracting muscle causes the fish body to undulate. These body undulations interact with the surrounding water to generate thrust. The resulting flow behind the swimming fish forms vortex rings, whose arrangement reflects the fish's swimming performance. Anguilliform swimmers shed individual vortex rings during steady swimming. Carangiform swimmers shed a connected chain of vortex rings. The currently available sections through the total flow fields are often not an honest representation of the total momentum in the water , the wake of carangiform swimmers shows a net backward momentum without the fish accelerating , suggesting that our current picture of the generated flow is incomplete. To accelerate, undulatory swimmers decrease the angle of the vortex rings with the mean path of motion, which is consistent with an increased rate of backward momentum transfer. Carangiform swimmers also enlarge their vortex rings to accelerate and to swim at a higher speed, while eel, which are anguilliform swimmers, shed stronger vortex rings. [source]

Comparison of the contractile properties, oxidative capacities and fibre type profiles of the voluntary sphincters of continence in the rat

JOURNAL OF ANATOMY, Issue 3 2010
Maria Buffini
Abstract The external urethral sphincter (EUS) and external anal sphincter (EAS) are the principal voluntary striated muscles that sustain continence of urine and faeces. In light of their common embryological origin, shared tonic sphincteric action and synchronized electrical activity in vivo, it was expected that they would exhibit similar physiological and structural properties. However, the findings of this study using paired observations of both sphincters isolated from the rat show clearly that this is not the case. The anal sphincter is much more fatigable than the urethral sphincter. On completion of a fatigue protocol, the amplitude of the last twitch of the EAS had declined to 42 ± 3% of the first twitch, whereas the last twitch of the EUS was almost identical to that of the first (95 ± 3%). Immunocytochemical detection of myosin heavy-chain isoforms showed that this difference was not due to the presence of more slow-twitch oxidative type 1 fibres in the EUS compared with the EAS (areal densities 4 ± 1% and 5 ± 1%, respectively; P = 0.35). In addition, the fatigue difference was not explained by a greater contribution to force production by fast oxidative type 2A fibres in the urethral sphincter. In fact, the anal sphincter contained a higher areal density of type 2A fibres (56 ± 5% vs. 37 ± 4% in the EUS, P = 0.017). The higher oxidative capacity of the EUS, measured histochemically, explained its fatigue resistance. These results were surprising because the fatigue-resistant urethral muscle exhibited faster single-twitch contraction times compared with the anal sphincter (56 ± 0.87 ms vs. 72.5 ± 1.16 ms, P < 0.001). Neither sphincter expressed the type 2X myosin isoform but the fast-twitch isoform type 2B was found exclusively in the EUS (areal density 16 ± 2%). The type 2B fibres of the EUS were small (diameter 19.5 ± 0.4 ,m) in comparison to typical type 2B fibres of other muscles. As a whole the EUS is a more oxidative than glycolytic muscle. In conclusion, analysis of the twitch mechanics and fatigue of two sphincters showed that the EUS contained more fatigue-resistant muscle fibres compared with the EAS. [source]

Pathophysiology and Disease Progression of Atrial Fibrillation: Importance of Achieving and Maintaining Sinus Rhythm

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 8 2008
F.A.C.C., MARC COHEN M.D.
Atrial fibrillation (AF) is a progressive disease in which arrhythmia-induced remodeling facilitates evolution from paroxysmal AF to persistent and permanent AF. Changes in electrical, structural, and contractile properties of cardiac tissue that are thought to underlie AF maintenance and progression are reviewed. Also examined is the negative impact of AF on clinical outcomes, as well as the potential benefits of restoration and maintenance of sinus rhythm. Because of the limited efficacy and adverse effects of current antiarrhythmics, new antiarrhythmic drugs need to be developed that provide safer and more effective rhythm control in AF. [source]

Mitochondrial function and apoptotic susceptibility in aging skeletal muscle

AGING CELL, Issue 1 2008
Béatrice Chabi
Summary During aging, skeletal muscle undergoes sarcopenia, a condition characterized by a loss of muscle cell mass and alterations in contractile function. The origin of these decrements is unknown, but evidence suggests that they can be partly attributed to mitochondrial dysfunction. To characterize the nature of this dysfunction, we investigated skeletal muscle contractile properties, subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondrial biogenesis and function, as well as apoptotic susceptibility in young (6 months old) and senescent (36 months old) Fischer 344 Brown Norway rats. Muscle mass and maximal force production were significantly lower in the 36-month group, which is indicative of a sarcopenic phenotype. Furthermore, contractile activity in situ revealed greater fatigability in the 36-month compared to the 6-month animals. This decrement could be partially accounted for by a 30% lower mitochondrial content in fast-twitch muscle from 36-month animals, as well as lower protein levels of the transcriptional coactivator peroxisome proliferator-activated receptor , coactivator-1,. Enzyme activities and glutamate-induced oxygen consumption rates in isolated SS and IMF mitochondria were similar between age groups. However, mitochondrial reactive oxygen species (ROS) production during state 3 respiration was ~1.7-fold greater in mitochondria isolated from 36-month compared to 6-month animals, and was accompanied by a 1.8-fold increase in the DNA repair enzyme 8-oxoguanine glycosylase 1 in fast-twitch muscle. Basal rates of release of cytochrome c and endonuclease G in SS mitochondria were 3.5- to 7-fold higher from senescent animals. These data suggest that the age-related sarcopenia and muscle fatigability are associated with enhanced ROS production, increased mitochondrial apoptotic susceptibility and reduced transcriptional drive for mitochondrial biogenesis. [source]

Properties of the two neuromuscular compartments in a split bipennate muscle

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2004
Barry P. Pereira
Abstract Bipennate muscles may be split along their distal aponeurosis, dividing each into two compartments. These sub-muscle units may be used in tendon transfers. This paper presents the contractile properties of the two sub-units of the flexor carpi ulnaris in a macaca fascicularis, after it was split by up to 80% of its length. The sub-muscle units were electrically stimulated and found to have independent isometric contraction, with minimal contraction recorded from the non-stimulated sub-unit. Also, the sum of the forces measured from each unit when stimulated individually, was found to be greater than the force of the whole muscle, given the same isometric conditions. The distal aponeurosis which is common allows force transmission between the compartments. Splitting the muscle along this distal aponeurosis alters this function and the force capacity of the muscle, providing a new potential for using the sub-units as grafts for tendon transfers. © 2004 Orthopaedic Research Society. Published y Elsevier Ltd. All rights reserved. [source]

Single muscle fiber size and contractility after spinal cord injury in rats

MUSCLE AND NERVE, Issue 1 2006
Walter R. Frontera MD
Abstract Spinal cord injury (SCI) results in muscle weakness but the degree of impairment at the level of single fibers is not known. The purpose of this study was to examine the effects of T9,level SCI on single muscle fibers from the tibialis anterior of rats. Significant decreases in cross-sectional area (CSA), maximal force (Po), and specific force (SF = Po/CSA) were noted at 2 weeks. Atrophy and force-generating capacity were reversed at 4 weeks, but SF remained impaired. Maximum shortening velocity (Vo) did not change after injury. SCI thus appears to affect various contractile properties of single muscle fibers differently. Normal cage activity may partially restore function but new interventions are needed to restore muscle fiber quality. Muscle Nerve, 2006 [source]

Myotonia and muscle contractile properties in mice with SIX5 deficiency

MUSCLE AND NERVE, Issue 4 2005
Kirkwood E. Personius PhD
Abstract Myotonic dystrophy (DM1) is an autosomal-dominant multisystem disease characterized by progressive skeletal muscle weakness, myotonia, cataracts, cardiac arrhythmias, mild mental retardation, and endocrinopathies. Heterozygous loss of SIX5 in mice causes cataracts and cardiac conduction disease, and homozygous loss also leads to sterility and decreased testicular mass, reminiscent of DM1 in humans. The effect of SIX5 deficiency in muscle is unknown. In this study, we found that muscle contractile properties, electromyographic insertional activity, and muscle histology were normal in SIX5 deficient mice. The implications of these findings for the pathogenesis of DM1 are discussed. Muscle Nerve, 2004 [source]

Mechanisms of force failure during repetitive maximal efforts in a human upper airway muscle

MUSCLE AND NERVE, Issue 1 2002
Christiana DelloRusso BS
Abstract The upper airway respiratory muscles play an important role in the regulation of airway resistance, but surprisingly little is known about their contractile properties and endurance performance. We developed a technique that allows measurement of force and the electromyogram (EMG) of human nasal dilator muscles (NDMs). Endurance performance was quantified by measuring NDM "flaring" force and EMG activity as healthy human subjects performed 10 s maximal voluntary contractions (MVCs), separated by 10 s rest, until the area under the force curve fell to 50% MVC (the time limit of the fatigue task, Tlim), which was reached in 34.2 ± 3.1 contractions (685.0 ± 62.3 s). EMG activity was unchanged except at Tlim, where it averaged 78.7 ± 3.6% of pretest activity (P < 0.01). M-wave amplitude did not change, suggesting that neuromuscular propagation was not impaired. MVC force increased to 80% of the pretest level within 10 min of recovery but twitch force failed to recover, suggesting low-frequency fatigue. The data suggest that a failure of the nervous system to excite muscle could explain at most only a small fraction of the NDM force loss during an intermittent fatigue task, and then only at Tlim. Thus, the majority of the force failure during this task is due to impairment of mechanisms that reside within the muscle fibers. © 2002 Wiley Periodicals, Inc. Muscle Nerve 26: 94,100, 2002 [source]

Contractile properties of human motor units in health, aging, and disease

Smooth muscle phenotypic plasticity in mechanical obstruction of the small intestine

NEUROGASTROENTEROLOGY & MOTILITY, Issue 7 2008
J. A. Macdonald
Abstract, Chronic, partial obstruction of the small intestine can dramatically alter peristaltic contractile properties. Morphological studies have revealed hypertrophy of the circular smooth muscle cells in the constricted part of the intestine. In this issue of Neurogastroenterology and Motility, Chen et al. show that hyperplasia and hypertrophy of intestinal smooth muscle cells occur at distinct times in response to partial obstruction of the ileum. Furthermore, the first evidence is provided to link intestinal smooth muscle remodelling during mechanical obstruction with changes in serum response factor and two of its co-regulating factors, myocardin and Elk-1. [source]

Contractile properties of the proximal urethra and bladder in female pig: Morphology and function

In vivo proteome dynamics during early bovine myogenesis

PROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 20 2008
Thibault Chaze
Abstract Myogenesis is a complex process of which the underlying mechanisms are conserved between species, including birds and mammals. Despite a good understanding of the stages of myogenesis, many of the mechanisms involved in the regulation of proliferation of the successive myoblast generations, the cellular transitions cell proliferation/alignment of myoblasts/fusion of myoblasts into myotubes/differentiation of myofibres and the control of total myofibre number still remain unknown. An in vivo proteomic analysis of the semitendinosus muscle from Charolais foetuses, at three specific stages of myogenesis (60, 110 and 180,days postconception), was conducted using 2-DE and MS. Expression profiles of more than 170 proteins were revealed and analysed using two way hierarchical clustering and statistical analysis. Our studies identify, for the first time, distinct proteins of varied biological functions and protein clusters with myogenic processes, such as the control of cell cycle activity and apoptosis, the establishment of cellular metabolism and muscle contractile properties and muscle cell reorganisation. These results are of fundamental interest to the field of myogenesis in general, and more specifically to the control of muscle development in meat producing animals. [source]

Comparison of protein expression in human deltoideus and vastus lateralis muscles using two-dimensional gel electrophoresis

PROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 10 2005
Daniele Capitanio
Abstract We have used two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS) to study the expression of contractile and regulatory proteins in human vastus lateralis and deltoideus muscles, in order to understand protein turnover and isoform switching in muscles with the same fiber-type composition but different functional properties. We demonstrate a two- to six-fold overexpression of enzymes associated with glycolysis, the tricarboxylic acid cycle, oxidative phosphorylation, and substrate transport in vastus lateralis compared to deltoideus. Expression levels of contractile protein isoforms correlated to the proportion of slow-twitch fibers in deltoideus compared to vastus lateralis are consistent with the different contractile properties of the two muscles. Two proteins involved in free radical homeostasis were differentially expressed, suggesting a direct relationship between radical scavenging and the muscle function. The application of 2-DE and MS to studies of muscle physiology thus offers a more comprehensive assessment of the molecular determinants of muscle function than traditional approaches. [source]

Differences in sodium voltage-gated channel properties according to myosin heavy chain isoform expression in single muscle fibres

THE JOURNAL OF PHYSIOLOGY, Issue 21 2009
F. Rannou
The myosin heavy chain (MHC) isoform determines the characteristics and shortening velocity of muscle fibres. The functional properties of the muscle fibre are also conditioned by its membrane excitability through the electrophysiological properties of sodium voltage-gated channels. Macropatch-clamp is used to study sodium channels in fibres from peroneus longus (PL) and soleus (Sol) muscles (Wistar rats, n= 8). After patch-clamp recordings, single fibres are identified by SDS-PAGE electrophoresis according to their myosin heavy chain isoform (slow type I and the three fast types IIa, IIx, IIb). Characteristics of sodium currents are compared (Student's t test) between fibres exhibiting only one MHC isoform. Four MHC isoforms are identified in PL and only type I in Sol single fibres. In PL, maximal sodium current (Imax), maximal sodium conductance (gNa,max) and time constants of activation and inactivation (,m and ,h) increase according to the scheme I,IIa,IIx,IIb (P < 0.05). ,m values related to sodium channel type and/or function, are similar in Sol I and PL IIb fibres (P= 0.97) despite different contractile properties. The voltage dependence of activation (Va,1/2) shows a shift towards positive potentials from Sol type I to IIa, IIx and finally IIb fibres from PL (P < 0.05). These data are consistent with the earlier recruitment of slow fibres in a fast-mixed muscle like PL, while slow fibres of postural muscle such as soleus could be recruited in the same ways as IIb fibres in a fast muscle. [source]

The time course of the motoneurone afterhyperpolarization is related to motor unit twitch speed in human skeletal muscle

THE JOURNAL OF PHYSIOLOGY, Issue 2 2003
E. Roderich Gossen
The relationship between the electrophysiological properties of motoneurones and their muscle units has been established in animal models. A functionally significant relationship exists whereby motoneurones with long post-spike afterhyperpolarizations (AHPs) innervate slow contracting muscle units. The purpose of this study was to determine whether the time course of the AHP as measured by its time constant is associated with the contractile properties of its muscle unit in humans. Using an intramuscular fine wire electrode, 46 motor units were recorded in eight subjects as they held a low force contraction of the first dorsal interosseus muscle for approximately 10 min. By applying a recently validated transform to the interspike interval histogram, the mean voltage versus time trajectory of the motoneurone AHP was determined. Spike-triggered averaging was used to extract the muscle unit twitch from the whole muscle force with strict control over force variability and motor unit discharge rate (interspike intervals between 120 and 200 ms). The AHP time constant was positively correlated to the time to half-force decay (,= 0.36, P < 0.05) and twitch duration (,= 0.57, P < 0.001); however, time to peak force failed to reach significance (,= 0.27, P < 0.07). These results suggest that a similar functional relationship exists in humans between the motoneurone AHP and the muscle unit contractile properties. [source]

Impaired myofibrillar function in the soleus muscle of mice with collagen-induced arthritis

ARTHRITIS & RHEUMATISM, Issue 11 2009
Takashi Yamada
Objective Progressive muscle weakness is a common feature in patients with rheumatoid arthritis (RA). However, little is known about whether the intrinsic contractile properties of muscle fibers are affected in RA. This study was undertaken to investigate muscle contractility and the myoplasmic free Ca2+ concentration ([Ca2+]i) in the soleus, a major postural muscle, in mice with collagen-induced arthritis (CIA). Methods Muscle contractility and [Ca2+]i were assessed in whole muscle and intact single-fiber preparations, respectively. The underlying mechanisms of contractile dysfunction were assessed by investigating redox modifications using Western blotting and antibodies against nitric oxide synthase (NOS), superoxide dismutase (SOD), 3-nitrotyrosine (3-NT), carbonyl, malondialdehyde (MDA), and S-nitrosocysteine (SNO-Cys). Results The tetanic force per cross-sectional area was markedly decreased in the soleus muscle of mice with CIA, and the change was not due to a decrease in the amplitude of [Ca2+]i transients. The reduction in force production was accompanied by slowing of the twitch contraction and relaxation and a decrease in the maximum shortening velocity. Immunoblot analyses showed a marked increase in neuronal NOS expression but not in inducible or endothelial NOS expression, which, together with the observed decrease in SOD2 expression, favors peroxynitrite formation. These changes were accompanied by increased 3-NT, carbonyl, and MDA adducts content in myofibrillar proteins from the muscles of mice with CIA. Moreover, there was a significant increase in SNO-Cys content in myosin heavy-chain and troponin I myofibrillar proteins from the soleus muscle of mice with CIA. Conclusion These findings show impaired contractile function in the soleus muscle of mice with CIA and suggest that this abnormality is due to peroxynitrite-induced modifications in myofibrillar proteins. [source]