Mechano-chemical coupling in spontaneous oscillatory contraction of muscle

Muscle cells take either one of two states, namely contraction (on-state) and relaxation (off-state), under a particular physiological condition (physiological ionic strength, neutral pH and a few mM MgATP). The transition between these two states is regulated by micromolar concentrations of free Ca²⁺. Here we review spontaneous oscillation phenomena named SPOC. The SPOC state is attained in a contractile system of muscle (muscle model without cell membrane) as a third intermediate state. It appears either at an intermediate concentration of free Ca²⁺ (Ca-SPOC) or under the coexistence of MgATP with its hydrolytic products, i.e., MgADP and inorganic phosphate (Pi), where Ca²⁺ is not required (ADP-SPOC). We have constructed a three-dimensional Phase diagram showing three regions corresponding to three states of muscle realized under various concentrations of MgADP, Pi and free Ca²⁺ in the presence of MgATP; the SPOC region was sandwiched between contraction and relaxation regions. We tried to understand the mechano-chemical coupling in SPOC by explaining the mechanical properties of SPOC based on a standard kinetic scheme of actomyosin ATPase; the experimental results could be well simulated, except for the function of Pi, by assuming that a particular kinetic step regulated by Ca²⁺ is also regulated by the feed-back effect of the actomyosin-ADP complex. It is suggested that the SPOC state is attained by cyclic transition among the different chemical states of the actomyosin complex within each half-sarcomere, which occurs spontaneously through the mechanochemical coupling characteristic to the actomyosin complex, i.e., a mechano-enzyme.     

Skeletal muscle contraction in protecting joints and bones by absorbing mechanical impacts

We have previously hypothesized that the dissipation of mechanical energy of external impact is a fundamental function of skeletal muscle in addition to its primary function to convert chemical energy into mechanical energy. In this paper, a mathematical justification of this hypothesis is presented. First, a simple mechanical model, in which the muscle is considered as a simple Hookean spring, is considered. This analysis serves as an introduction to the consideration of a biomechanical model taking into account the molecular mechanism of muscle contraction, kinetics of myosin bridges, sarcomere dynamics, and tension of muscle fibers. It is shown that a muscle behaves like a nonlinear and adaptive spring tempering the force of impact and increasing the duration of the collision. The temporal profiles of muscle reaction to the impact as functions of the levels of muscle contraction, durations of the impact front, and the time constants of myosin bridges closing, are obtained. The absorption of mechanical shock energy is achieved due to the increased viscoelasticity of the contracting skeletal muscle. Controlling the contraction level allows for the optimization of the stiffness and viscosity of the muscle necessary for the protection of the joints and bones.     

Mechanism of the calcium-regulation of muscle contraction — In pursuit of its structural basis —

The author reviewed the research that led to establish the structural basis for the mechanism of the calcium-regulation of the contraction of striated muscles. The target of calcium ions is troponin on the thin filaments, of which the main component is the double-stranded helix of actin. A model of thin filament was generated by adding tropomyosin and troponin. During the process to provide the structural evidence for the model, the troponin arm was found to protrude from the calcium-depleted troponin and binds to the carboxyl-terminal region of actin. As a result, the carboxyl-terminal region of tropomyosin shifts and covers the myosin-binding sites of actin to block the binding of myosin. At higher calcium concentrations, the troponin arm changes its partner from actin to the main body of calcium-loaded troponin. Then, tropomyosin shifts back to the position near the grooves of actin double helix, and the myosin-binding sites of actin becomes available to myosin resulting in force generation through actin-myosin interactions.     

The influence of middle-ear muscle contraction on auditory threshold for selected pure tones

The influence of middle-ear muscle (MEM) contraction on auditory threshold has been measured for pure tones of 0.25, 0.5, and 1.5 kHz. The reflex-activating signal was a 3-kHz pure tone. Signal paradigms were chosen to reduce or eliminate the effects of binaural loudness summation, contralateral direct masking, and contralateral remote and backward masking effects, and to maximize the influence of MEM contraction. Results indicate that under no condition was behavioral threshold affected by the MEM contraction induced using a pure-tone stimulus of 3 kHz, 105 dB SPL.     

Unilateral cricothyroid contraction and glottic configuration

It is frequently stated that unilateral cricothyroid muscle (CT) paralysis can be diagnosed by physical examination, noting rotation of the glottis, and shortening and vertical displacement of the ipsilateral vocal fold. These signs, however, are inconsistently observed, and there is considerable controversy regarding the direction of glottic rotation. To determine the effects of CT contraction on three-dimensional glottic configuration, we performed computerized tomography on cadaver larynges before and after simulated CT contraction. Radiopaque makers were used to compute distances. Unilateral CT contraction equally increased the length of both membranous vocal folds, and rotated the posterior glottis less than 1 mm. CT contraction neither adducted the vocal processes, nor significantly their altered vertical level. These results suggest that unilateral CT paralysis cannot be diagnosed on the basis of any clinically apparent change in glottal configuration.     

Mechanochemical model for myosinⅡdimer that can explain the spontaneous oscillatory contraction of muscle

The spontaneous oscillatory contraction(SPOC) of myofibrils is the essential property inherent to the contractile system of muscle. Muscle contraction results from cyclic interactions between actin filament and myosin II which is a dimeric motor protein with two heads. Taking the two heads of myosin II as an indivisible element and considering the effects of cooperative behavior between the two heads on rate constants in the mechanochemical cycle, the present work proposes the tenstate mechanochemical cycle model for myosin II dimer. The simulations of this model show that the proportion of myosin II in different states periodically changes with time, which results in the sustained oscillations of contractive tension, and serves as the primary factor for SPOC. The good fit of this model to experimental results suggests that the cooperative interaction between the two heads of myosin II dimer may be one of the underlying mechanisms for muscle contraction.     

A three-phase single sheet tester with digital control of flux loci based on the contraction mapping principle

Tight control of flux loci in 2D testing of soft magnetic laminations is realized by a method based on the principle of contraction mapping. It is implemented through digital control of the currents supplying a three-phase yoke magnetizer and the use of circular samples. Faithful realization of the prescribed loci and good measuring accuracy are demonstrated in grain-oriented and non-oriented Fe–Si laminations.     

Basic connection between superconductivity and superfluidity

A basic and inherently simple connection is shown to exist between superconductivity and superfluidity. It is shown that the author's previously derived general equation, which agrees well with the superconducting transition temperatures for the heavy-electron superconductors, metallic superconductors, oxide superconductors, metallic hydrogen, and neutron stars, also works well for the superfluid transition temperature of 2.6 mK for liquid³He. Reasonable estimates are made from 10^–3 to 10⁹ K — a range of 12 orders of magnitude. The same paradigm applies to the superfluid transition temperature of liquid⁴He, but results in a slightly different equation. The superfluid transition temperature for dilute solutions of³He in superfluid⁴He is estimated to be l–10K. This paradigm works well in detail for metallic, cuprate, and organic superconductors.     

FT-IR study of the effect of zinc exposure on the biochemical contents of the muscle of Labeo rohita

Heavy metal pollution is a major environmental problem in the modern world due to increasing human activities. Zinc is an essential element involved in a wide variety of cellular processes. However, it becomes toxic when elevated concentrations are introduced into the environment. The goal of the present study is to investigate the effect of zinc exposure on the biochemical contents of the muscle tissues of freshwater species Labeo rohita using Fourier transform infrared (FT-IR) spectroscopy. Since the muscle constitutes the greatest mass of the fish that is consumed, the present study has paid particular attention to muscle component. The result reveals that the zinc exposure causes significant changes in the biochemical contents of the L. rohita muscle tissues. In addition, it causes an alteration in the protein secondary structures by decreasing the α-helix and increasing the β-sheet contents of muscle tissues. Further, it has been observed that the administration of chelating agent D-penicillamine improves the protein and lipid contents in the muscle tissues compared to zinc exposed tissues. This result shows that D-penicillamine is the effective chelator of zinc in reducing the body burden of L. rohita fingerlings.     

Length-tension relationship of the feline thyroarytenoid muscle

Vocal fold tension during phonation is generated by coordinated contraction of the intrinsic laryngeal muscles. The thyroarytenoid muscle has been found to have increased stiffness at various levels of strain when compared with other intrinsic laryngeal muscles. The objective here is to test the hypothesis that the thyroarytenoid muscle exhibits high passive tension during maximal isometric tetanic force generation, and to test the hypothesis that the thyroarytenoid maintains the ability to generate contractile force at high levels of strain more effectively than other skeletal muscle. The thyroarytenoid muscles (n=9) and digastric muscle strips (n=7) were removed from adult random-bred cats. Maximal isometric tension and passive tension at optimum length were measured from each muscle in vitro. Active and passive length-tension curves were constructed for each muscle. The contractile properties of the thyroarytenoid group were compared with those of the digastric muscle group. The thyroarytenoid muscle group required on average 140 mN of passive tension to generate maximal isometric tetanic tension. This represented 39% of the average maximal isometric tetanic tension generated by the muscles. These results were significantly higher than the digastric muscle group, which required on average 28 mN of passive tension (9% of maximal isometric tetanic tension, p<0.05). At 110% of optimum length, the thyroarytenoid muscle maintained 89.8% of maximal isometric tetanic force, whereas the digastric muscle group maintained 67.7% of maximal isometric tetanic force (p<0.05). The thyroarytenoid muscle exhibits higher passive tension when generating maximal isometric tension than the digastric muscle control group. The thyroarytenoid muscle maintains higher levels of active tension at high strain than the digastric muscle control group. We conclude that these findings are related to the ability of the thyroarytenoid muscle to function as a fine tensor of the vocal fold in a high strain environment.     

Relationships between Changes in Oxygenation during Exercise and Recovery in Trained Athletes

The purpose of this study was to investigate the relationships of rate of deoxygenation determined using near-infrared spectroscopy (NIRS) during isometric contraction exercise (Rate_deoxy) with maximal muscle strength, muscle thickness and muscle oxidative capacity of knee extensors in eight well-trained male athletes. The subjects performed sustained isometric extension at 30% and 50% of the maximal voluntary contraction (MVC) load for 10s and 30 repetitive maximal isokinetic knee extensions. Rate_deoxy in the final 5s of 30% MVC was negatively correlated with maximal muscle strength, muscle thickness of knee extensors and the half-time of deoxygenation recovery (T1/2) determined by NIRS after 30 repetitive maximal isokinetic contractions, defined as muscle oxidative capacity. The results suggest that Rate_deoxy during submaximai isometric contraction reflects muscle aerobic capacity.     

Conjugacy and stability theorems in connection with contraction of lie algebras

Let $\text{a ? Г}{}_{\mathrm{n}}\text{(}\text{g}\text{?}\text{)}$, the n-dimensional Grassmannian variety, and ? be a Lie algebra of the dimension m?n. We study some properties of the set $\text{B <}\text{G(a)}$, where $\text{G(a)}$ is the Zariski closure of the orbit of $\text{G=GL(}\text{g}\text{?}\text{)}$ at the point a. The group GL(?) is the group of automorphisms of ?. The set B is shown to be the set of Lie algebras which are contractions of ā. ā is a subalgebra of ?. The main results are formulated in theorems on the conjugacy of contracted algebras and stability of the Lie algebra ā under contraction. The conjugacy theorem relates the algebras in the set B.     

Observation of magnetic field-induced contraction of fission yeast cells using optical projection microscopy

The charges in live cells interact with or produce electric fields, which results in enormous dielectric responses, flexoelectricity, and related phenomena. Here we report on a contraction of Schizosaccharomyces pombe (fission yeast) cells induced by magnetic fields, as observed using a phase-sensitive projection imaging technique. Unlike electric fields, magnetic fields only act on moving charges. The observed behavior is therefore quite remarkable, and may result from a contractile Lorentz force acting on diamagnetic screening currents. This would indicate extremely high intracellular charge mobilities. Besides, we observed a large electro-optic response from fission yeast cells.     

Group contraction and the nine Cayley-Klein geometries

A one-to-one correspondence between the nine Cayley-Klein geometries and the so-called kinematic groups is presented. As is well known, the kinematic groups are related to each other through group contraction. The pattern of contraction is explained by relating each kinematic group to a specific Cayley-Klein geometry. The very meaning of group contraction is deeply rooted in the relationship between the nine geometries. Lie algebras of those geometries are explicitly constructed.In part from the Tesina de LicenciaturaM. A. Fernandez Sanjuan, Tesina de Licenciatura: Contracciones anisötropas del grupo de Poincar, Universidad de Valladolid, 1981.     

Simulated effects of cricothyroid and thyroarytenoid muscle activation on adult-male vocal fold vibration

Adjustments to cricothyroid and thyroarytenoid muscle activation are critical to the control of fundamental frequency and aerodynamic aspects of vocal fold vibration in humans. The aerodynamic and physical effects of these muscles are not well understood and are difficult to study in vivo. Knowledge of the contributions of these two muscles is essential to understanding both normal and disordered voice physiology. In this study, a three-mass model for voice simulation in adult males was used to produce systematic changes to cricothyroid and thyroarytenoid muscle activation levels. Predicted effects on fundamental frequency, aerodynamic quantities, and physical quantities of vocal fold vibration were assessed. Certain combinations of these muscle activations resulted in aerodynamic and physical characteristics of vibration that might increase the mechanical stress placed on the vocal fold tissue.     

Challenges for detection of neuronal currents by MRI

Neuronal current MRI (nc-MRI) is an imaging method that directly maps magnetic field changes caused by neuronal currents with, at the same time, a high spatial and temporal resolution. A viable nc-MRI method would be of great benefit, both for the study of human brain function and for clinical applications in the field of epilepsy, especially for the noninvasive presurgical mapping of epileptogenic foci. A survey of fundamental issues in nc-MRI is reviewed, and challenges for future developments of the method are described within this context. Particularly, an overview of the models for signal generation is given, and the origin and physiology of different sources of neuronal currents are described. Prospects for predicting neuronal currents by electromagnetic field mapping and using this information, both a priori and a posteriori, for nc-MRI are considered. Ways of increasing specificity in nc-MRI by minimizing secondary hemodynamic and metabolic effects are described as well as means of optimizing the nc-MRI method for pushing the detection limit. Previously published works are described within these categories and future directions for nc-MRI are proposed.     

Effects of thermal contraction on structure and properties of PET fibers

A series of poly(ethylene terephthalate) fibers of various molecular weights was first drawn to a practical maximum draw ratio and then allowed to contract thermally under tension for 10, 20, and 38%. These contracted fibers exhibit a high degree of plasticity even when tested at—100°C and extension rates of 1300%/sec. An attempt is made to explain this behavior by means of a systematic study of morphological changes which occur during thermal contraction. The interpretation of the results of small-angle and wide-angle x-ray diffractions, infrared spectroscopy, and birefringence suggest the existence of two types of amorphous domains; those separating the adjacent crystallites in the microfibril and those separating the microfibrils. It is speculated that the molecules in these two domains respond differently to thermal effects and stress, and that the interfibrillar amorphous domain consists of highly extended molecules.

It is shown that the thermal contraction, which does not involve major changes in the degree of crystallinity, proceeds by several mechanisms. At low degrees of contraction, the most important mechanism is the contraction of the microfibrils. At high levels of contraction, the shrinkage proceeds to a large degree via relative displacement of the microfibrils and the contraction of extended interfibrillar tie molecules.

The conclusions regarding the structure of these fibers are corroborated by means of transmission electron microscopy of thin cross-sections.     

Spatial heterogeneity in the muscle functional MRI signal intensity time course: effect of exercise intensity

It has previously been observed that during isometric dorsiflexion exercise, the time course of T2-weighted signal intensity (SI) changes is spatially heterogeneous. The purpose of this study was to test the hypothesis that this spatial heterogeneity would increase at higher contraction intensities. Eight subjects performed 90-s isometric dorsiflexion contractions at 30% and 60% of maximum voluntary contraction (MVC) while T2-weighted (repetition time/echo time=4000/35 ms) images were acquired. SI was measured before, during and after the contractions in regions of interest (ROIs) in the extensor digitorum longus (EDL) muscle and the deep and superficial compartments of the tibialis anterior (D-TA and S-TA, respectively). For all ROIs at 30% MVC, SI changes were similar. The maximum postcontraction SI was greater than the SI during exercise. At 60% MVC, SI changes during contraction were greater in the S-TA than in the D-TA and EDL. For the EDL and D-TA, the maximum postcontraction SI was greater than those during exercise. For the S-TA, the maximum postcontraction change was greater than the changes at t=8, 20 and 56 s but not the end-exercise value. We conclude that spatial heterogeneity increases during more intense dorsiflexion contractions, possibly reflecting regional differences in perfusion or neural activation of the muscle.     

使用超声估计肌肉疲劳的初步研究

表面肌电信号把神经肌肉活动和肌肉收缩联系起来，已被视为一种估计肌肉疲劳比较客观的方法，但也存在一些不足。另一方面，超声已广泛应用于医学诊断和研究，在骨骼肌方面也有不少研究报道，但还未见文献报道超声用于肌肉疲劳的估计。本文介绍一套自行开发的新的同步连续采集B超图像、力矩和肌电信号的采集系统，并利用它对肱二头肌的肌肉疲劳进行了估计。试验表明在30秒的肌肉疲劳过程中，肌肉厚度会以非线性的方式增加。