Contractile Phenomena Research Articles

A novel kinetic model to demonstrate the independent effects of ATP and ADP/Pi concentrations on sarcomere function.

Understanding muscle contraction mechanisms is a standing challenge, and one of the approaches has been to create models of the sarcomere-the basic contractile unit of striated muscle. While these models have been successful in elucidating many aspects of muscle contraction, they fall short in explaining the energetics of functional phenomena, such as rigor, and in particular, their dependence on the concentrations of the biomolecules involved in the cross-bridge cycle. Our hypothesis posits that the stochastic time delay between ATP adsorption and ADP/Pi release in the cross-bridge cycle necessitates a modeling approach where the rates of these two reaction steps are controlled by two independent parts of the total free energy change of the hydrolysis reaction. To test this hypothesis, we built a two-filament, stochastic-mechanical half-sarcomere model that separates the energetic roles of ATP and ADP/Pi in the cross-bridge cycle's free energy landscape. Our results clearly demonstrate that there is a nontrivial dependence of the cross-bridge cycle's kinetics on the independent concentrations of ATP, ADP, and Pi. The simplicity of the proposed model allows for analytical solutions of the more basic systems, which provide novel insight into the dominant mechanisms driving some of the experimentally observed contractile phenomena.

Understanding altered contractile properties in advanced age: insights from a systematic muscle modelling approach

Age-related alterations of skeletal muscle are numerous and present inconsistently, and the effect of their interaction on contractile performance can be nonintuitive. Hill-type muscle models predict muscle force according to well-characterised contractile phenomena. Coupled with simple, yet reasonably realistic activation dynamics, such models consist of parameters that are meaningfully linked to fundamental aspects of muscle excitation and contraction. We aimed to illustrate the utility of a muscle model for elucidating relevant mechanisms and predicting changes in output by simulating the individual and combined effects on isometric force of several known ageing-related adaptations. Simulating literature-informed reductions in free Ca2+ concentration and Ca2+ sensitivity generated predictions at odds qualitatively with the characteristic slowing of contraction speed. Conversely, incorporating slower Ca2+ removal or a fractional increase in type I fibre area emulated expected changes; the former was required to simulate slowing of the twitch measured experimentally. Slower Ca2+ removal more than compensated for force loss arising from a large reduction in Ca2+ sensitivity or moderate reduction in Ca2+ release, producing realistic age-related shifts in the force-frequency relationship. Consistent with empirical data, reductions in free Ca2+ concentration and Ca2+ sensitivity reduced maximum tetanic force only slightly, even when acting in concert, suggesting a modest contribution to lower specific force. Lower tendon stiffness and slower intrinsic shortening speed slowed and prolonged force development in a compliance-dependent manner without affecting force decay. This work demonstrates the advantages of muscle modelling for exploring sources of variation and identifying mechanisms underpinning the altered contractile properties of aged muscle.

The Myofibroblast: TGFβ-1, A Conductor which Plays a Key Role in Fibrosis by Regulating the Balance between PPARγ and the Canonical WNT Pathway

Myofibroblasts are non-muscular contractile cells that occur physiologically in organs such as in stem villi of the human placenta during normal pregnancies. They have the ability to contract and relax in response to changes in the volume of the intervillous chamber. Myofibroblasts are also found in many pathological states, and are involved in wound healing and fibrosis processes in several organs such as liver, lung, kidney, and heart. During fibrosis, the contractile phenomenon is a relaxation-free mechanism, associated with the synthesis of collagen in the extracellular matrix (ECM), which leads to irreversible fibrosis, tissue retraction and finally apoptosis of the myofibroblasts. The molecular motor of myofibroblasts is the non-muscle myosin type II (NMII). Differentiation of fibroblasts into myofibroblast is largely regulated by the Transforming Growth Factor-β1 (TGF-β1). This system regulates the canonical WNT/β-catenin pathway in a positive manner and PPARγ in a negative manner. WNT/β-catenin promotes fibrosis while PPARγ prevents fibrosis. This review focuses on the contractile properties of myofibroblasts and on the TGF-β1 conductor which regulates the antagonism between PPARγ and the canonical WNT/β-catenin pathway.

Actomyosin based contraction: one mechanokinetic model from single molecules to muscle?

Bridging the gaps between experimental systems on different hierarchical scales is needed to overcome remaining challenges in the understanding of muscle contraction. Here, a mathematical model with well-characterized structural and biochemical actomyosin states is developed to that end. We hypothesize that this model accounts for generation of force and motion from single motor molecules to the large ensembles of muscle. In partial support of this idea, a wide range of contractile phenomena are reproduced without the need to invoke cooperative interactions or ad hoc states/transitions. However, remaining limitations exist, associated with ambiguities in available data for model definition e.g.: (1) the affinity of weakly bound cross-bridges, (2) the characteristics of the cross-bridge elasticity and (3) the exact mechanistic relationship between the force-generating transition and phosphate release in the actomyosin ATPase. Further, the simulated number of attached myosin heads in the in vitro motility assay differs several-fold from duty ratios, (fraction of strongly attached ATPase cycle times) derived in standard analysis. After addressing the mentioned issues the model should be useful in fundamental studies, for engineering of myosin motors as well as for studies of muscle disease and drug development.Electronic supplementary materialThe online version of this article (doi:10.1007/s10974-016-9458-0) contains supplementary material, which is available to authorized users.

筋収縮の基本原理から筋弛緩を考える

日頃使い慣れている筋弛緩薬といえども，知らないことや忘れていることも意外に多い．本学会の教育講演では，筋弛緩薬の基礎的な知識から臨床使用法まで幅広く体系的に理解できるように企画した．本稿では，筋収縮のメカニズム，筋弛緩薬の効果発現と薬物動態，薬物動態から見た筋弛緩薬の至適投与量と拮抗薬スガマデクスの効果に関して要点を概説する．

Impaired but reversible vascular reactivity in a rat model of microgravity

Background: The hindlimb unweighting (HLU) rat model mimics cardiovascular deconditioning following microgravity or human bed rest, particularly for the development of orthostatic intolerance. We have examined vascular responses to α1 adrenergic and non-α1 adrenergic agonists in vitro. We have also explored the reversibility of the contractile abnormalities observed. Methods: Dose-response curves were generated to phenylephrine (PE) and norepinephrine (NE) (10 −9 to 10 −4 M), U46619 (U4) (10 −10 to 10 −6 M) at one-half log order intervals in controls (n = 6), HLU (n = 6), or recovered rats (n = 6). EC50s and maximal responses (Emax) were calculated by nonlinear logistic regression analysis with PRIZM software (Graphpad, Mountain View, CA). Results: Simulated microgravity results in attenuated contractile responses to both α1 adrenergic and non-α1 adrenergic agonists, but the impaired contractile phenomenon reverses with time. Conclusions: The decreased vascular reactivity after microgravity and prolonged bed rest could cause attenuated baroreflex function and produce orthostatic intolerance, but that problem resolved with time. (Korean J Anesthesiol 2008; 55: 602～6)

Megakaryocyte-restricted MYH9 inactivation dramatically affects hemostasis while preserving platelet aggregation and secretion

AbstractMutations in the MYH9 gene encoding the nonmuscle myosin heavy chain IIA result in bleeding disorders characterized by a macrothrombocytopenia. To understand the role of myosin in normal platelet functions and in pathology, we generated mice with disruption of MYH9 in megakaryocytes. MYH9Δ mice displayed macrothrombocytopenia with a strong increase in bleeding time and absence of clot retraction. However, platelet aggregation and secretion in response to any agonist were near normal despite absence of initial platelet contraction. By contrast, integrin outside-in signaling was impaired, as observed by a decrease in integrin β3 phosphorylation and PtdIns(3,4)P2 accumulation following stimulation. Upon adhesion on a fibrinogen-coated surface, MYH9Δ platelets were still able to extend lamellipodia but without stress fiber–like formation. As a consequence, thrombus growth and organization, investigated under flow by perfusing whole blood over collagen, were strongly impaired. Thrombus stability was also decreased in vivo in a model of FeCl3-induced injury of carotid arteries. Overall, these results demonstrate that while myosin seems dispensable for aggregation and secretion in suspension, it plays a key role in platelet contractile phenomena and outside-in signaling. These roles of myosin in platelet functions, in addition to thrombocytopenia, account for the strong hemostatic defects observed in MYH9Δ mice.

Differences in the profile of unfused tetani of fast motor units with respect to their resistance to fatigue in the rat medial gastrocnemius muscle.

In most studies performed on motor units in mammalian muscles the division of these units into fast and slow types has been based on the 'sag' visible in the profile of unfused tetanus. The time course of the sag in unfused tetani of fast motor units was analysed in the present study. Fast units of rat medial gastrocnemius muscle were classified as fast fatigable (FF) or fast resistant to fatigue (FR) on the basis of a fatigue index calculated during the standard fatigue test. In middle-fused tetani (fusion index 0.25-0.75), it was observed that for FF motor units the sag was shorter and occurred earlier than for FR units. Moreover, in FF units, the sag was followed by potentiating tension, whereas for FR units this potentiation was weaker or even absent. A tetanus shape index, which expressed the ratio of the area of the first part of the tetanus record (between the tension record and the baseline, from the beginning of tetanus up to the lowest point during the sag in the tension record) to the area under the second part of tetanus (from this lowest point up to the end of the record) was introduced. For FF units, this index ranged from 0.13 to 0.47, whereas for FR units it ranged from 0.54 to 17.8 (with one exception). These results showed that the difference in unfused tetanus expressed in this tetanus shape index could be used as an accurate alternative method of dividing fast units into FF and FR groups. Moreover, the difference in sag time course in FF and FR groups. Moreover, the difference in sag time course in FF and FR units suggests that the metabolism responsible for this contractile phenomenon is significantly different time courses in IIa and IIb muscle fibres, constituting FF and FR units, respectively.

Transforming growth factor-beta induction of alpha-smooth muscle actin is dependent on the deformability of the collagen matrix.

Current evidence suggests that fibroblasts undergo phenotypic modulation during several physiologic and pathologic conditions, such as wound healing and fibrocontractive diseases [29]. These phenotypically altered fibroblasts develop cytoskeletal features similar to those of smooth muscle cells (SMCs), including the expression of α-smooth muscle actin (α-SMA), which is a contractile isoform of actin and, hence, they have been denoted as myofibroblasts [8]. The myofibroblast is thought to contribute to the process of wound contraction, as well as contractile phenomena observed during fibrotic diseases. However, little is known about the mechanisms responsible for phenotypic modulation of fibroblasts and the expression of α-SMA. Several types of growth factors and cytokines that are locally released from inflammatory and stromal cells at wound sites, as well as components of the extracellular matrix, have been studied to evaluate their role in fibroblastic differentiation. A likely candidate for regulation of α-SMA is transforming growth factor-β (TGF-β) [7], a potent regulator of matrix remodeling. This regulation may be achieved in part by modulation of cell-matrix interactions.

Implications of quantal motor action in biological systems.

We demonstrate in this paper that quantal behavior is a central feature of biological motile and contractile systems. Step-like behavior has been demonstrated in the interaction between single molecules and filaments both in the kinesin-microtubule system and in the myosin-actin filament system. We show here that the step-like molecular features appear also in the single intact sarcomere. We studied single sarcomeres of single bumble-bee myofibrils, both in the unactivated and activated states. Myofibril-length changes induced by a motor-imposed ramp were accompanied by corresponding sarcomere-length changes. However, the sarcomere-length changes were stepwise. Computer analysis of the stepwise shortening patterns revealed a step-size distribution containing multiple peaks. In the activated state, the peaks were separated by 2.7 nm per half-sarcomere which is the linear actin-subunit spacing. Thus, translation steps are an integer multiple of the actin-subunit spacing. This result parallels the one observed in the kinesin-tubulin spacing, where step size is a multiple of the tubulin-subunit spacing. In the muscle system, however, the steps are preserved on a macroscopic scale, implying high synchrony. The quantal steps are easily explained by a model in which the actin filament propels itself over stationary cross-bridges: if actin binds to the cross-bridges between steps, then the observed quantal result is inevitable. As probes of contractile phenomena approach the molecular level, the discrete unitary events underlying contraction begin to emerge. Thus, step-like behavior is observed as the single kinesin molecule translates along the microtubule, as the single myosin molecule translates over the actin filament, and as the single isolated titin molecule is stretched.

Characteristics of the contractile response of rabbit aorta produced by cromakalim in calcium-free solution.

1 The effect of potassium channel opening compounds has been investigated in the smooth muscle of rabbit aorta under Ca-free conditions. Examination of the characteristics of the response has been performed using cromakalim as the prototype compound. 2 In order of potency, Ro 31-6930, cromakalim, minoxidil sulphate and pinacidil each produced a contraction in rabbit aortic strips bathed in Ca-free MOPS-buffered physiological salt solution (PSS). In contrast, forskolin, glyceryl trinitrate and nifedipine each failed to increase tension under identical conditions. Cromakalim also evoked contraction of bovine trachealis muscle bathed in Ca-free PSS. 3. The contractile response to cromakalim in rabbit aortic strips was of delayed onset (15-20 min) and reached a plateau after approximately 120 min (1.8 g maximum with 1 microM cromakalim). No cromakalim-induced tension changes were observed in either 1 mM or 2.5 mM Ca-containing PSS. 4. Raising the [KCl] of the Ca-free PSS to 65.9 mM fully inhibited the cromakalim-induced contraction in rabbit aortic strips. In addition, pretreatment of aortic strips with the sulphonylurea glibenclamide antagonized the subsequent mechanical response to cromakalim. 5. In Ca-free PSS, cromakalim (1 microM) stimulated 42K-efflux with a time-course corresponding to the contractile event. Glibenclamide (1 microM) inhibited this cromakalim-induced 42K-efflux. 6. In sharp microelectrode studies in bovine trachealis, cromakalim (10 microM) produced a sustained membrane hyperpolarization in normal PSS. In contrast, the cromakalim-induced hyperpolarization in Ca-free PSS was not sustained. The fading of the hyperpolarization was temporally correlated with the increase in tension under these experimental conditions. 7. It is concluded that the K-channel opener-induced smooth muscle contractile response revealed in Ca-free PSS is the consequence of K-channel opening. The nature of the detailed mechanism which underlies this contractile phenomenon remains to be determined.

The contribution of mitochondrial calcium ion exchange to relaxation of tension in cardiac muscle.

The possible contribution of mitochondrial Ca2+ accumulation and release to contractile phenomena has been investigated. Two intracellular fractions of Ca2+ sequestration can be identified in cardiac myocytes, one ascribed to mitochondria. Two modes of Ca2+ transport exist within the mitochondrial fraction, one dependent upon mitochondrial respiration and the other upon extramitochondrial [Na+]. Experiments with trabeculae show that under appropriate conditions, the rate of relaxation and the amount of tension developed is dependent on these two modes of Ca2+ transport. A model is presented quantifying the contribution of the mitochondria to relaxation.

Seasonal changes in the effects of arginine vasotocin and stretch on Anolis uterine contractions in vitro.

We determined the effects of acute stretch on spontaneous and arginine vasotocin (AVT)-driven contractions of the Anolis carolinensis uterus in vitro. Whole uteri from reproductively inactive females (October) were placed in a bath of oxygenated 32 degrees C Anolis "Ringer's." Two initial tensions were utilized, 1.5 g or 15 g, the latter being an estimate of the tension on the wall of a uterine compartment. Uteri were then exposed to either saline or AVT (50 ng/ml), and spontaneous or AVT-driven contractions were recorded for 20 min with the use of a strain gauge and physiograph. A similar experiment was performed on uteri from reproductively active females in the summer (June). Our results indicate that the effects of acute stretch and AVT on uterine contractility were qualitatively similar in summer and fall. That is, AVT induced a tonic contraction; stretch decreased the duration of the tonic contraction; the saline-treated uteri exhibited spontaneous rhythmic contractions; AVT increased the amplitude of the rhythmic contractions, but only at the lower tension; there were no effects of AVT on the timing (contraction interval, duration, rest interval) of the rhythmic contractions; and stretch increased the frequency of the rhythmic contractions. Season greatly influenced the magnitude of these contractile phenomena. Uteri tested during the breeding season exhibited greater distensibility, an increase in the amplitude and duration of the AVT-driven tonic contraction, and an increase in the frequency of both spontaneous and AVT-driven rhythmic contractions because of a decrease in both contraction duration and rest interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluorescence resonance energy transfer measurements of distances in actin and myosin. A critical evaluation.

The contractile proteins actin and myosin are of considerable biological interest. They are essential for muscle contraction and in eukaryotic cells they play a crucial role in most contractile phenomena. Over the years since the first fluorescence resonance energy transfer (FRET) paper appeared, an extensive body of literature has accumulated on this technique using actin, myosin and the actomyosin complex. These papers are reviewed with several aims in mind: we assess the reliability and consistency of intra- and inter-molecular distances measured between the fluorescent probes attached to specific sites on these proteins; we determine whether the measurements can be assembled into an internally consistent model which can be fitted to the known dimensions of the actomyosin complex; several of the FRET distances are consistent with the available structural data from crystallographic and electron microscopic dimensions; the modelled FRET distances suggest that the assumed value of the orientation factor (k2 = 2/3) is reasonable; we conclude that the model has a predictive value, i.e. it suggests that a small number of the published dimensions may be incorrect and predicts the magnitude of a larger number of measurements which have not yet been reported; and finally (vi) we discuss the contribution of FRET determinations to the current debate on the molecular mechanism of contraction.

Phase relations of oscillatory contraction cycles inPhysarumplasmodia: I. a serial infrared registration device and its application to different plasmodial stages

Abstract A new and inexpensive electronic device is described which enables serial registrations of the oscillatory contraction activities at closely neighbouring sites within plasmodia of Physarum polycephalum. At the same time, this new construction allows the immediate automatic transformation of the original sinusoidal contraction curves into multiple phase graphs. The application on different stages of plasmodia reveals phase gradients as a characteristic phenomenon especially in isolated objects. The investigation of plasmodial strands without endoplasm demonstrates that the radial activities represent active contractile phenomena of the ectoplasmic tube.

37] Ligand-induced patching and capping of surface immunoglobulins

This chapter discusses the patching and capping phenomena that has been described for a variety of membrane components in a number of different cell types. The basic model remains, however, the patching and capping of membrane immunoglobulin (mIg) la of B lymphocytes. With other membrane components, the conditions for obtaining such redistribution phenomena may be significantly different. The chapter states that a detailed model for the mechanisms of patching and capping, and related membrane phenomena such as pinosome formation, microvilli formation, endocytosis, and shedding, has also been developed. The chapter reviews the general characteristics of the capping phenomenon, particularly the energy requirements, temperature dependence, inhibition, reversion by microfilament-directed drugs, and the accumulation of microfilaments under the cap that have led to the suggestion that capping is probably a cellular contractile phenomenon. The role of microtubules in the capping phenomenon is more complex and they do not appear to enhance microfilament mobility but rather to inhibit it. Capping of any membrane component probably occurs as a consequence of microprecipitation resulting in entrapment within the lattice formed in the plasma membrane, of a microfilament-associated membrane component: the “membrane capping component” or “integral protein X.” The hypothesis has been formulated, however, that not only clustered components but also whole domains of membrane might be brought into the cap.

Demonstration of actin in the fibroblasts of healing palatal wounds.

The purpose of this study was to gain information which might be helpful in understanding the influence of palate surgery on abnormal maxillary growth. The finding of actin-rich cells in the granulation tissue of palatal wounds supports the hypothesis that one of the functions of those cells is contraction--and the latter subsequently leads to convergence of the wound margins and aberrations in growth of the underlying skeletal tissue. Much additional information is needed for final proof of that hypothesis. At present little is known about the initiation, regulation, or control of the proposed contractile phenomena, or the process of aberrent maxillary growth. Such information will be necessary for further development of clinical techniques that will allow normal maxillofacial growth after surgery on the palate at an early age.

Reparative Processes in Mammalian Wound Healing: The Role of Contractile Phenomena

This chapter summarizes the major advances in the understanding of several aspects of reparative processes made in the last few years. Humans, as well as other vertebrates, do not possess a great power of cell or organ regeneration when compared with lower species, and repair of a loss of tissue is essentially made by the synthesis of connective tissue which abrogates the volume discontinuities and keeps together the margins of the remaining parenchymas. Only some tissues, such as epidermis, are capable of regenerating over the scar and reconstituting the continuity lost with the wound. In general, the healing of a wound consists of two interconnected phenomena: (1) synthesis and/or regeneration of tissues which replace the damaged ones, and (2) remodeling of these tissues to restore the form of the body. The relative importance of these phenomena may vary. In cutaneous linear wounds or in wounds of areas firmly adherent to deeper planes, the reduction in spatial discontinuity is due to the local growth of granulation tissue and epithelium, whereas in large wounds of mobile areas of the skin, or in ischemic lesions of the myocardium, the reduction in spatial discontinuity is mostly due to wound contraction. The reparative events are generally preceded by hemostatic and inflammatory phenomena which may in turn influence the final result of wound healing.

Membrane ionic permeabilities and contractile phenomena in myocardium.

Membrane ionic permeabilities and contractile phenomena in myocardium.

Muscle Contraction produced by Sulphydryl Inhibitors

IT was recently reported1 that the sulphydryl (—SH) agent, parachloromercuribenzoate (PCMB), causes superprecipitation of actomyosin gel. Masking of an —SH group appears to prevent interaction between ATP and some inhibitory site on the protein, thus enabling ATP to induce superprecipitation through reaction with another site. If this phenomenon is related to changes occurring in the actomyosin system during muscle activity, then —SH agents should be expected to produce contraction. Accordingly, several such agents were tested on skeletal muscle, and they were found to cause various types of contractile phenomena.