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PubMed1967

Filament ultrastructure and organization in vertebrate smooth muscle. Contraction hypothesis based on localization of actin and myosin.

Using a variety of preparative techniques for electron microscopy, we have obtained evidence for the disposition of actin and myosin in vertebrate smooth muscle. All longitudinal myofilaments seen in sections appear to be actin. Previous reports of two types of longitudinal filaments in sections are accounted for by technical factors, and by differentiated areas of opacity along individual filaments. Dense bodies with actin emerging from both ends have been identified in homogenates, and resemble Z discs from skeletal muscle (Huxley, 1963). In sections, short, dark-staining lateral filaments 15-25 A in diameter link adjacent actin filaments within dense bodies and in membrane dense pataches. They appear homologous with Z-disc filaments. Similar lateral filaments connect actin to plasma membrane. Dense bodies and dense patches, therefore, are attachment points and denote units analogous to sarcomeres. In glycerinated, methacrylate-embedded sections, lateral processes different in length and staining characteristics from lateral filaments in dense bodies exist at intervals along actin filaments. These processes are about 30 A wide and resemble heavy meromyosin from skeletal muscle. They also resemble heads of whole molecules of myosin in negatively stained material from gizzard homogenates. Intact single myosin molecules and dimers have been found, both free and attached to actin, even in media of very low ionic strength. Myosin can, therefore, exist in relatively disaggregated form. Models of the contraction mechanism of smooth muscle are proposed. The unique features are: (1) Myosin exists as small functional units. (2) Movement occurs by interdigitation and sliding of actin filaments.

Animals↗
PubMed2006

Muscle fibre recruitment can respond to the mechanics of the muscle contraction.

This study investigates the motor unit recruitment patterns between and within muscles of the triceps surae during cycling on a stationary ergometer at a range of pedal speeds and resistances. Muscle activity was measured from the soleus (SOL), medial gastrocnemius (MG) and lateral gastrocnemius (LG) using surface electromyography (EMG) and quantified using wavelet and principal component analysis. Muscle fascicle strain rates were quantified using ultrasonography, and the muscle-tendon unit lengths were calculated from the segmental kinematics. The EMG intensities showed that the body uses the SOL relatively more for the higher-force, lower-velocity contractions than the MG and LG. The EMG spectra showed a shift to higher frequencies at faster muscle fascicle strain rates for MG: these shifts were independent of the level of muscle activity, the locomotor load and the muscle fascicle strain. These results indicated that a selective recruitment of the faster motor units occurred within the MG muscle in response to the increasing muscle fascicle strain rates. This preferential recruitment of the faster fibres for the faster tasks indicates that in some circumstances motor unit recruitment during locomotion can match the contractile properties of the muscle fibres to the mechanical demands of the contraction.

Adult↗
PubMed2000

Bone surface strains and internal bony pressures at the jaw joint of the miniature pig during masticatory muscle contraction.

The long-standing debate on whether the jaw joint is loaded is due in part to the complexity of the factors involved, including a number of different muscles, each with a potentially unique role. This study sought to elucidate how two major jaw muscles, the masseter and the lateral pterygoid, influence jaw-joint loading. Twenty-five 10-month-old miniature pigs were divided into two groups, controls and pigs with the lateral capsular ligament of the jaw joint stripped surgically; this was expected to affect loading by destabilizing the joint. Rosette strain gauges were bonded to: (1) the lateral surface of the squamosal bone (equivalent to the squamosal portion of the temporal bone in humans) at the level of the articular eminence; (2) the lateral surface of the condylar neck; and (3) the lateral surface of the mandibular corpus below the molar region. Semiconductor pressure transducers were placed underneath the surfaces of the anterior slope of the condyle and the posterior slope of the articular eminence through drilled holes. Strains and internal bony pressures were recorded during stimulated tetanic contractions of the masseter or lateral pterygoid muscles. Masseter contraction, either alone or with the contralateral muscle, caused net tension in the squamosal bone and net compression in the condylar neck. The orientations were approximately vertical to the occlusal plane. Masseter contraction elevated both the condylar and eminence pressures from their resting values. The strains caused by lateral pterygoid contractions were much smaller than for the masseter with the exception of the condylar location. Ipsilateral lateral pterygoid contraction decreased both the condylar and eminence pressures from their resting values, perhaps because condylar movement altered the contact between the joint surfaces. Surgical disruption enhanced both pressure changes and bone strains under either muscle contraction but their overall patterns were not altered. In conclusion, both strains and pressures in the jaw joint varied according to specific muscle activity.

Analysis of Variance↗
PubMed1991

Effect of low extracellular calcium and ryanodine on muscle contraction of the mouse during postnatal development.

We have examined the effects of low Ca2+ solutions, Co2+, and ryanodine on the isometric tension and contraction speed of isolated, developing mouse EDL muscles. Twitch responses of young muscles (7-14 days postnatal) were more sensitive to lowered [Ca2+]o than those of more fully developed muscles (22-35 days postnatal). Responses of EDL muscles from a middle-aged group (15-21 days postnatal) were intermediate between the two other groups. Overall, the time course of contraction in a single twitch was accelerated by low [Ca2+]o. Ca(2+)-free solution induced a 7.95 and 9.25 mV depolarization in young and "old" muscle fibres, respectively. The presence of cobalt ions (5 mM) in the Krebs solution had a similar effect as Ca(2+)-free Krebs in terms of reduction of the isometric twitch and tetanic tensions of EDL muscles from the various age groups. In contrast, the shortening of the contraction time seen with Ca(2+)-free solution did not take place following exposure to Co(2+)-containing solutions. Finally, young (7-14 days postnatal) muscles were less sensitive to the inhibitory action of ryanodine on the twitch compared with more fully developed muscles (22-35 days postnatal). Taken together, our results indicate that from birth to maturity, there is a gradual change in the spectrum of calcium utilization for the contractile process.

Animals↗
PubMed1990

Myosin heads have a broad orientational distribution during isometric muscle contraction: time-resolved EPR studies using caged ATP.

To study the orientation of spin-labeled myosin heads in the first few seconds after the production of saturating ATP, we have used a laser flash to photolyze caged ATP during EPR data acquisition. Rabbit psoas muscle fibers were labeled with maleimide spin label, modifying 60% of the myosin heads without impairing muscle fiber biochemical and physiological activity (ATPase and force). The muscle bundles were incubated for 30 min with 5 mM caged ATP prior to the UV flash. The flash, from an excimer laser, liberated 2-3 mM ATP, generating maximum force in the presence of Ca2+ and relaxing fully in the absence of Ca2+. Control experiments, using fibers decorated with labeled myosin subfragment, showed that the flash liberates sufficient ATP to saturate myosin active sites in all regions of the muscle bundles. To increase the time resolution, and to minimize the time of the contraction, we followed in time the intensity at a single spectral position (P2), which is associated with the high degree of orientational order in rigor. ATP liberation produced a rapid decrease of P2 with liberation of ATP, indicating a large decrease in orientational order in both relaxation and contraction. This transient was absent when caged AMP was used, ruling out nonspecific effects of the UV flash and subsequent photochemistry. The steady-state level of P2 during contraction was almost as low as that reached in relaxation, although the duration of the steady state was much more brief in contraction. Upon depletion of ATP in contraction, the P2 intensity reverted to the original rigor level, accompanied by development of rigor tension. The steady-state results obtained in the brief contractions induced by caged ATP are quantitatively consistent with those obtained in longer contractions by continuously perfusing fibers with ATP. In isometric contraction, most (88% +/- 4%) of the heads are in a population characterized by a high degree of axial disorder, comparable to that observed for all heads in relaxation. Since the stiffness of these fibers in contraction is 80% of the stiffness in rigor, it is likely that most of the heads in this highly disoriented population are attached to actin in contraction and that most actin-attached heads in contraction are in this disoriented population.

Adenosine Triphosphate↗
PubMed2003

Reflex muscle contractions can be elicited by valgus positional perturbations of the human knee.

Experimental evidence on the reflex responses of thigh muscles to valgus mechanical perturbations at the human knee are presented. Random step positional deflections, ranging from 5 degrees to 12 degrees at 60 degrees /s, were applied to the fully extended knees of seven healthy subjects. Subjects were instructed to maintain a constant background co-activation ( approximately 2-11% MVC) of the quadriceps and hamstring muscles prior to and during the mechanical stimulus. We found that the reflex response to sustained valgus joint deflection in the vasti muscles had longer onset latencies (range: 83-92ms) than did the stretch reflex in the same muscles (latencies: 29-31ms). This reflex EMG response consisted typically of a peak followed by sustained muscle activity throughout the step perturbation. The sustained EMG activity was dependent on the amplitude of the perturbing stimulus, but in a nonlinear manner. The long latency of the valgus response suggests that the reflex originates in nonmuscular sensory pathways, potentially from mechanoreceptors lying in periarticular tissues such as joint ligaments and capsule. Analysis of the spatial distribution of reflex responses showed an asymmetrical pattern with preferential activation of medial vs. lateral muscles of the knee. We assess whether these asymmetric reflex contractions could promote joint stability, either by inducing generalized joint stiffening, or by preferential activation of those muscles that are best suited to resist induced ligament strain.

Adult↗
PubMed1998

Effects of newly synthesized amino acids containing thiazole residues on electrically evoked smooth muscle contractions.

New amino acids containing thiazole residues have been synthesized and in vitro experiments were performed to study their action on neurotransmission in target tissues with adrenergic and cholinergic neurotransmission. Acetaminothiazoles, structurally related to the novel class, are known to act as H1 agonists, therefore, the effects of the newly synthesized Ala- and Pro-thiazole derivatives on smooth muscle contractile activity were compared to those of histamine (HA). The experiments were carried out on electrically stimulated prostatic part of rat and rabbit vasa deferentia and proximal guinea pig ileum. HA had biphasic effect on electrically evoked neurogenic contractions of guinea pig ileum, Pro(Thz) had a stimulating effect, while Ala(Thz) had no effect. The histamine H1-receptor antagonist diphenhydramine inhibited the Pro(Thz)-induced spontaneous contractile activity in the longitudinal layer of guinea pig ileum. HA had a biphasic effect on electrically induced neurogenic contractions of rat and rabbit vasa deferentia while Pro(Thz) and Ala(Thz) inhibited the ES-contractions. The present results show that the newly synthesized compounds might affect the electrically evoked smooth muscle contractions. Some similarity in the effects of HA and of the new substances was observed.

Amino Acids↗
PubMed1977

Maximum isometric knee flexor and extensor muscle contractions: normal patterns of torque versus time.

Isometric torque of the knee flexor and extensor muscles were recorded for 5 seconds at three knee joint positions. The subjects included healthy men in age groups from 20 to 35 and 45 to 65 years of age. The amplitudes and duration of peak torque and the time to peak torque were measured for each contraction. Peak torque was usually maintaned less than 0.1 second and never longer than 0.9 second. At each of the three angles, the mean extensor muscle torque was higher than the mean flexor muscle torque in both age groups, and the mean torque for both muscle group was higher among the younger than among the older man. The highest average torque was recorded at the knee angle of 60 degrees for the extensor muscles and 45 degrees for the flexor muscles, but this was not always a stereotyped response either for a given individual or among individuals.

Adult↗
PubMed1981

Estimation of myodynamic parameter values from observations on isometrically contracting muscle groups.

A new method is presented which makes it possible to estimate from a series of experimental observations of isometric maximum-effort muscle torque, a set of myodynamic parameter values for each of a number of muscles contributing collectively to the total torque output. The parameters that can be estimated are: the individual maximum isometric forces; the spreads of the length-tension curves; the relative maximum isometric tendon extensions; and the optimum muscle lengths; most of which parameters could not be estimated previously. The method is described for both penniform and fusiform muscles, and is demonstrated using the human triceps muscle as an example. The values obtained by this method are in general agreement with comparable values obtained by in vitro methods.

Adult↗
PubMed1986

[Hysteretical properties of muscle contraction during continuous and intermittent efferent stimulation].

Hysteretical effects were studied on the ankle extensor muscle of the anesthetized cat. Continuous and intermittent stimulations were applied to efferents supplying these muscles; linear sinusoidal and step changes of the length were used. Stiffness of the muscle could became negative when the muscle was stretched above the resting length provided that the intermittent stimulation was used. If the same length was achieved under conditions of continuous stimulation, the stiffness was invariably positive. Effectiveness of the intermittent stimulation was higher as compared with continuous one in shortening phases of length changing. The observed hysteretical effects are discussed from the functional point of view.

Animals↗
PubMed1993

Inhibition by 2,3-butanedione-monoxime of mitochondrial ADP-dependent respiration and muscle contraction.

2,3-Butanedione-monoxime (BDM) inhibits tension development in skeletal, cardiac and smooth muscle. Experiments on isolated single fibres of frog-muscle have shown a use dependent intermittent failure of twitching during continued stimulation. Our analysis of the effect of BDM on rabbit liver mitochondria and submitochondrial particles revealed a reduction of oxygen consumption in coupled mitochondria stimulated by adding of ADP, while in uncoupled mitochondria the oxygen consumption was not inhibited by BDM. Furthermore the substance did not inhibit ATP hydrolysis by submitochondrial particles. Based on these findings we suggest that BDM inhibits the activity of the mitochondrial ATP/ADP translocase.

Adenosine Diphosphate↗
PubMed2000

Differential effects of muscle contraction from various body parts on neuromagnetic somatosensory responses.

We studied eight healthy subjects with a whole-scalp 306-channel neuromagnetometer to explore the effect of motor activity from different body parts on somatosensory responses to left median nerve stimulation. The stimuli produced clear tactile sensation without any motor movement. In the rest condition, the subject had no task. During contraction conditions, the subject had to maintain submaximal isometric contraction in masseter, left deltoid, left thenar, or left tibialis muscles. Short-latency responses from the primary somatosensory cortex did not change during contraction. Responses from both the right (contralateral) and left second somatosensory cortices (SII) were significantly enhanced during contraction of the left thenar muscles. Responses from the left SII were significantly enhanced also during contraction of the left deltoid muscles, but they were decreased during contraction of the masseter and left tibialis anterior muscles. This study implies that SII activation is modulated by motor activity and that the effect depends on the topographical proximity of the stimulated and contracted body parts.

Adult↗
PubMed1994

Actin-severing and Ca(2+)-induced reversal of smooth muscle contraction that is independent of Ca2+.

1. Intracellular actin filament organization of gastric smooth muscle cells of the guinea pig in primary culture was examined with rhodamine-labelled phalloidin using a confocal laser fluorescence microscope. 2. The resting cells, both in the presence and absence of Ca2+, showed an even distribution of microfilamentous actin fibers. 3. The characteristic image of the stimulated cells with 10 microM acetylcholine in the presence of 1.8 mM Ca2+ was that the actin filaments were located only on the periphery of the cell. 4. The characteristic image of the cells stimulated as above, but in the absence of Ca2+, was that the actin filaments were unevenly distributed in the cell. 5. The characteristic image of the cells stimulated in the presence of 1 microM Ca2+, which inhibits the above contraction, was pultaceous with the actin filaments absent, indicating severing of actin filaments by a Ca(2+)-activated system, such as gelsolin.

Actins↗
PubMed1988

Inosine and adenosine formation in ischemic and non-ischemic contracting muscles of rats: difference between fast and slow muscles.

Inosine and adenosine formation was evaluated in different types of rat skeletal muscle during ischemic and non-ischemic contraction. Extensor digitorum longus (EDL, fast) and soleus (slow) muscles were stimulated electrically via the sciatic nerve (5 Hz, 10 min). Under non-ischemic condition, the concentrations of IMP, inosine, adenosine, and hypoxanthine increased in EDL muscles but not in soleus muscles during stimulation. Under ischemic condition, these metabolites increased in both EDL and soleus muscles, although the increases in IMP and inosine were greater in EDL muscles. The increase in inosine had a strong positive correlation with that in IMP in ischemic EDL and soleus muscles, but the ratio, delta inosine/delta IMP was smaller in EDL muscles. The increase in adenosine under ischemic condition was not significantly different between the two muscles. These findings suggest that ischemia enhances degradation of purine nucleotides in contracting fast and slow muscles, and that although the degradation of purine nucleotides to IMP is greater in fast muscles than in slow muscles, the relative degradation rate of IMP to inosine is rather smaller in fast muscles.

Adenosine↗
PubMedDate not supplied

[Changes in the energetics of muscle contraction as a result of hyperoxia].

Using a highly sensitive thermometric method (1 X 10(-5) degrees C/mm), it was found that the heat production of a single isometric contraction of an isolated diaphragm of the rats exposed to 99% O2 at normal pressure for 3 and 6 hrs significantly differed from the norm: after 3 hr hyperoxygenation muscle heat production increased almost three-fold, and after 6 hr hyperoxygenation it decreased almost two-fold. The increase is regarded as a result of oxygen-potentiated increase of energy expenditures involved in a contraction and of a decrease of the performance of muscle contraction. The decrease is considered as a consequence of the primary in economical energy expenditures by an intensively working muscle represented by the diaphragm and of a reduced viability of the muscle preparation incubated in vitro.

Animals↗
PubMed1994

Magnesium and lithium antagonism of carbachol- and electrically-induced smooth muscle contractions in the rat gastrointestinal tract.

The pharmacological actions of lithium and magnesium have been investigated using isolated smooth muscle preparations from the rat gastrointestinal tract. Tissue contraction was evoked by means of carbachol or electrical field stimulation and the degree of inhibition of contraction caused by lithium was measured. Lithium effects were compared with those of the chemically similar ions, magnesium and calcium, by manipulation of the physiological buffer solutions. Lithium antagonism was enhanced when tissue contractile mechanisms were dependent on extracellular calcium concentration in the bathing fluid. This suggests that lithium is acting at the cell membrane by preventing calcium entry via ion channels. These results are consistent with evidence from clinical studies which indicate low cellular accumulation of lithium at therapeutic concentrations.

Animals↗
PubMed1981

Drugs that block smooth muscle contraction inhibit in vivo ovulation in hamsters.

We have demonstrated previously that smooth muscle cells (SMC) in the base of hamster follicles contract minutes before ovulation. The contraction of these cells correlates well in time with the development of a constriction in the base of the follicle. The purpose of this study was to determine whether contraction of SMC (1) produces this constriction and (2) is necessary for ovulation. We treated preovulatory hamster ovaries with six classes of drugs (lanthanides, calcium antagonists, local anesthetics, prostaglandins, cAMP modulators, and cytochalasin B) known to inhibit SMC contraction in other tissues. Drugs were injected into the experimental bursal cavity of a hamster 3 hours before ovulation; the contralateral ovary received no treatment and served as a control. Three hours after ovulation, the number of ruptured follicles on experimental and control ovaries were compared by light and electron microscopy. All the smooth muscle (SM) inhibitors, except those that affect cAMP levels and cytochalasin B, prevented (1) contraction of follicular SM, (2) constriction of the base of the follicle, and (3) ovulation. These results support the idea that contraction of follicular SMC constricts the follicle and is required for ovulation. The results further show that follicular SMC are activated by an influx of extracellular calcium and that prostaglandin F2 alpha may be involved in promoting this contraction.

Animals↗