Academic literature on the topic 'Fast-to-slow transformation'

AbstractMuscle fibre types can transform from slow-twitch (slow myosin heavy chain (MyHC)) to fast-twitch (fast MyHC) or vice versa. Leucine plays a vital effect in the development of skeletal muscle. However, the role of leucine in porcine myofibre type transformation and its mechanism are still unclear. In this study, effects of leucine and microRNA-27a (miR-27a) on the transformation of porcine myofibre type were investigatedin vitro. We found that leucine increased slow MyHC protein level and decreased fast MyHC protein level, increased the levels of phospho-protein kinase B (Akt)/Akt and phospho-forkhead box 1 (FoxO1)/FoxO1 and decreased the FoxO1 protein level. However, blocking the Akt/FoxO1 signalling pathway by wortmannin attenuated the role of leucine in porcine myofibre type transformation. Over-expression of miR-27a decreased slow MyHC protein level and increased fast MyHC protein level, whereas inhibition of miR-27a had an opposite effect. We also found that expression of miR-27a was down-regulated following leucine treatment. Moreover, over-expression of miR-27a repressed transformation from fast MyHC to slow MyHC caused by leucine, suggesting that miR-27a is interdicted by leucine and then contributes to porcine muscle fibre type transformation. Our finding provided the first evidence that leucine promotes porcine myofibre type transformation from fast MyHC to slow MyHC via the Akt/FoxO1 signalling pathway and miR-27a.

Two Ca2+-dependent signaling pathways, mediated by the Ca2+-activated phosphatase calcineurin and by the Ca2+-activated kinase Ca2+/calmodulin-dependent kinase (CaMK), are both believed to function in fast-to-slow skeletal muscle fiber type transformation, but questions about the relative importance of the two pathways still remain. Here, the differential gene expression during fast-to-slow fiber type transformation was studied using cultured adult flexor digitorum brevis (FDB) fibers and a custom minimicroarray system containing 21 fiber type-specific marker genes. After 3 days of culture, unstimulated fibers showed a generally slower gene expression profile; 3 days of electric field stimulation of cultured FDB fibers with a slow fiber-type pattern transformed the fibers to an even slower gene expression profile. Unstimulated FDB fibers overexpressing constitutively active calcineurin featured a slower gene expression profile, except four genes, indicating that transformation occurred, but was incomplete with activation of the calcineurin pathway alone. In both unstimulated FDB fibers and slow-type electrically stimulated FDB fibers, blocking of CaMK pathway with KN93 generated a faster gene expression profile compared with the negative control KN92, indicating that CaMK pathway functions during the transformation induced by both unstimulated culturing and slow fiber-type electrical stimulation. Moreover, neither the calcineurin nor the CaMK pathway alone could maximally activate the transformation, and coordination of the two pathways is required to accomplish a complete fast-to-slow fiber type transformation.

Skeletal muscle consists of different fiber types arranged in a mosaic pattern. These fiber types are characterized by specific functional properties. Slow-type fibers demonstrate a high level of fatigue resistance and prolonged contraction duration, but decreased maximum contraction force and velocity. Fast-type fibers demonstrate a high contraction force and velocity, but profound fatigability. During the last decades, it has been discovered that all these properties are determined by the predominance of slow or fast myosin-heavy-chain (MyHC) isoforms. It was observed that gravitational unloading during space missions and simulated microgravity in ground-based experiments leads to the transformation of some slow-twitch muscle fibers into fast-twitch ones due to changes in the patterns of MyHC gene expression in the postural soleus muscle. The present review covers the facts and mechanistic speculations regarding myosin phenotype remodeling under conditions of gravitational unloading. The review considers the neuronal mechanisms of muscle fiber control and molecular mechanisms of regulation of myosin gene expression, such as inhibition of the calcineurin/NFATc1 signaling pathway, epigenomic changes, and the behavior of specific microRNAs. In the final portion of the review, we discuss the adaptive role of myosin phenotype transformations.

AbstractThe Brusselator with different time scales, which behaves in the classical slow-fast effect, is investigated, and is characterized by the coupling of the quiescent and spiking states. In order to reveal the generation mechanism by using the slow-fast analysis method, the coordinate transformation is introduced into the classical Brusselator, so that the transformed system can be divided into the fast and slow subsystems. Furthermore, the stability condition and bifurcation phenomenon of the fast subsystem are analyzed, and the attraction domains of different equilibria are presented by theoretical analysis and numerical simulation respectively. Based on the transformed system, it could be found that the generation mechanism between the quiescent and spiking states is Fold bifurcation and change of the attraction domain of the fast subsystem. The results may also be helpful to the similar system with multiple time scales.

Reiser, Peter J., William O. Kline, and Pal L. Vaghy.Induction of neuronal type nitric oxide synthase in skeletal muscle by chronic electrical stimulation in vivo. J. Appl. Physiol. 82(4): 1250–1255, 1997.—Fast-twitch skeletal muscles contain more neuronal-type nitric oxide synthase (nNOS) than slow-twitch muscles because nNOS is present only in fast (type II) muscle fibers. Chronic in vivo electrical stimulation of tibialis anterior and extensor digitorum longus muscles of rabbits was used as a method of inducing fast-to-slow fiber type transformation. We have studied whether an increase in muscle contractile activity induced by electrical stimulation alters nNOS expression, and if so, whether the nNOS expression decreases to the levels present in slow muscles. Changes in the expression of myosin heavy chain isoforms and maximum velocity of shortening of skinned fibers indicated characteristic fast-to-slow fiber type transformation after 3 wk of stimulation. At the same time, activity of NOS doubled in the stimulated muscles, and this correlated with an increase in the expression of nNOS shown by immunoblot analysis. These data suggest that nNOS expression in skeletal muscle is regulated by muscle activity and that this regulation does not necessarily follow the fast-twitch and slow-twitch pattern during the dynamic phase of phenotype transformation.

Slow-tonic anterior latissimus dorsi (ALD) muscle properties were studied following chronic spinal cord stimulation in chick embryo. Stimulation at a fast rhythm was applied from day 7, 8 or 10 of development until the end of embryonic life. When stimulation was applied from day 7 up to day 18 of development, ALD muscle exhibited at day 18 a large decrease in half time to peak of tetanic contraction, a large proportion of fast type II fibres and an increase in fast myosin light chain content as compared to control muscle. When stimulation started at day 8 of development, changes in properties of ALD muscle were reduced when compared to the previous experimental series. Indeed, no fast type II fibres were observed within the muscle, even when stimulation was prolongated until the 20th day of embryonic development. In addition, chronic stimulation at a fast rhythm initiated at day 10 of development did not modify ALD muscle differentiation. The present results indicate that a fast pattern of motor neurone activity can induce some slow-to-fast transformations of ALD muscle fibres. However, after the first week of embryonic life, ALD myotubes appeared refractory to these transformations. The possible mechanisms responsible for the transformation of slow myotubes and for their further loss of plasticity are discussed.

Since increased muscle activity, which results in fast-slow fiber transformation, is associated with increases in sarcoplasmic Ca2+ concentration ([Ca2+]i), it seemed of interest to study the level of [Ca2+] after cessation of stimulation in fibers of the extensor digitorum longus muscle chronically stimulated (8 Hz). [Ca2+]i was measured in individual fibers with a Ca2+-sensitive electrode after subtracting the membrane potential, measured simultaneously from the potential of the Ca2+ electrode. During the first 14 days of stimulation, [Ca2+]i increased from approximately 0.1 to 0.5 microM and declined in approximately 3 wk to a value slightly higher than the initial one. The rise and decline of [Ca2+]i was preceded by a transient increase in total calcium. If stimulation was terminated after 7-8 wk when an essentially complete fast-to-slow transformation had taken place, a subsequent rest period led to a reverse slow-to-fast transformation, which was also preceded by a transient increase of [Ca2+]i reaching a peak at day 5 of rest. Unstimulated fast and slow fibers and fully transformed fibers do not differ in their [Ca2+] levels; thus it appears that the transformation process itself is accompanied, particularly in its earlier stages, by elevated [Ca2+]i levels. Elucidation of the relation between changes in Ca2+ and changes in gene expression will require further work.

Skeletal muscle is a heterogeneous, multinucleated, post-mitotic tissue that contains many functionally diverse fibre types that are capable of adjusting their phenotypic properties in response to altered contractile demands. This plasticity, or adaptability of skeletal muscle is largely dictated by variations in motoneuron firing patterns. For example, in response to increased tonic firing of slow motoneurons, which occurs during bouts of endurance training or chronic low-frequency stimulation (CLFS), skeletal muscle adapts by transforming from a faster to a slower phenotypic profile. CLFS is an animal model of endurance training that induces fast-to-slow fibre type transformations in the absence of fibre injury in the rat. The underlying signaling mechanisms regulating this fast-to-slow fibre type transformation, however, remain to be fully elucidated. It has been suggested that myogenic stem cells, termed satellite cells, may regulate and/or facilitate this transformational process. Therefore, the signaling mechanisms involved in CLFS-induced satellite cell activation as well as the role satellite cells may play in CLFS-induced skeletal muscle adaptation were investigated in rat. A pharmacological inhibitor of nitric oxide (NO) synthase, Nω-nitro-L-arginine methyl ester, was used to investigate CLFS-induced satellite cell activation in the absence of endogenous NO production. Results suggest that NO is required for early CLFS-induced satellite cell activation, but a yet-to-be defined pathway exists that is able to fully compensate in the absence of prolonged NO production. A novel method of satellite cell ablation (i.e. weekly focal γ-irradiation application) was used to investigate CLFS-induced skeletal muscle adaptation in the absence of a viable satellite cell population. Myosin heavy chain (MHC), an important structural and regulatory protein component of the contractile apparatus, was used as a cellular marker of the adaptive response to CLFS. Findings suggest that satellite cell activity may be required for early fast-to-slow MHC-based transformations to occur at the protein level without delay in the fast fibre population, and may also play an obligatory role in the final transformation from fast type IIA to slow type I fibres. Interestingly, additional results show that NO appears to be a key mediator of MHC isoform gene expression during CLFS-induced fast-to-slow fibre type transformations.

The author explains the purport of the article. He intends to emulate the style of Descartes to the extent possible in the contemporary setup. In his 10 meditations the author attempts to grasp vital capacities of Descartes’ method and to that effect to better understand his intellectual achievements and their current relevance. Cartesian moment or creative impact of Descartes upon dynamics of intellectual advancement is a key moment (point in time) that separates old scholastic ways of reasoning from modern ones as Martin Heidegger amply affirmed in his «The Age of the World Picture». Modern way not only relies on ratio but also on individual creative abilities and personal authorship of an investigator. Hence the author explores creative capabilities of a modern researcher typified by Descartes. The author defines Cartesian methodological practice (style, manner) as distinctly personalized and to that effect subjective or self-centered. This novel methodological artifice of Descartes is coupled with typically modern distinction between subjective (personally biased) and subjectival (pertaining to an independent agency of emancipating personality or subject). Investigating self of Descartes intentionally exploits typically modern cognitive and social property of being a free cognitive agent. It may be called cognitive agency or subjectness ( субъектность , subjectnost’ ) as a counterpart to subjectivity ( субъективность , subjectivnost’ ). Respectively Heidegger while discussing unique Cartesian achievement introduces along a casual notion of subjectivity self-coined terms of Subjektsein (subject-object relations, Subjekt-Objekt-Beziehung) and Subjektität (resolute self-awareness, unbedingtes Sichwissen). It is characteristic that Heidegger carefully discriminates spontaneous personally biased Ichheit and Egoismus from consistently individually conceived Ichhaft. The article examines two epitomes of subjectness: the initial Cartesian archetype and recent Wittgensteinian prototype. While Descartes instrumentally uses it to reshape scholastic thought into a modern metaphysics (cf. «Meditationes de Prima Philosophia» of 1641 or its authorized French translation of 1647 «Les méditations métaphysiques» ), Wittgenstein respectively elaborates his own brand of philosophy of logic (cf. « Logisch-Philosophische Abhandlung » of 1921). With Descartes his actual person is nothing but ‘being on his own’ ( ens per se ). Pragmatically this difference transmutes into operation of the actual whole self of the researcher ( me totum ) with development of polar metaphysical abstractions of non-bodily and non-extensive res cogitans and bodily and non-thinking res extensa . With Wittgenstein the equally pivotal personality of researcher reduces into an intermediator (border, Grenze ) between the world and the transcendental logic. As a result, metaphysical subject (metaphysisches Subjekt) or solipsist me (Ich des Solipsismus) shrinks into a non-extensive dot (Punkt) or eye (Auge) observing the world from outside. While new-born Cartesian cognitive agent has to split within itself into res cogitans and res extensa Descartes’ disciples and followers simply ignore bodily dimension. They radically reduce the investigating self to a detached all-powerful Reason turning subjectival Cartesianism of its founder into a non-subjectival version of Cartesianism, supposedly objective and rational. Wittgenstein helps the investigator (his personal self) come back again but at the expense of limiting himself to a border between the logic and the world able to reconstruct both the logic and the world with incessant language games. In his fifth meditation the author emulates both the style and the way of reasoning typical for Descartes. He remembers his student years in Moscow Lomonosov University. First he has mastered phonological principle of distinctive features and then successfully extended its use beyond linguistics into social studies and political science. Being taught dual - fast and slow reading he learnt to skip and then to restore details. The third personal cognitive discretion utilized in investigation of any scholarly issue is the focus on its emergence, further metamorphoses and evolution. The first two have clear Cartesian formation, while the third helps them both to gain dynamism and discretions. Next meditation deals with Descartes’ idea of the (definite article) method and specific rules for applying inherent inventiveness ( rēgulae ad directionem ingenii ). This Cartesian link implies essential affinity between universal instrumentality (organon) of scientific exploration and fundamental (primeval and primitive) cognitive abilities of humans and other species. Such a polarized dual distinction has helped the Center of advanced methodologies to identify three complex transdisciplinary organons (metretics, morphetics and semiotics) rooted in the elementary cognitive abilities to tell intensity of sensations, to recognize patterns and to grasp functional relevance, potentially meaning. Simplex-complex transformations devised by the Center are instrumental in linking the utmostly complex phenomena to equally simple ones through the range of intermediate manifestations and forms. The results of the analytical transformations can be revealed in the sequences of modules related to a master prototype model. The concluding two meditations deal with cognition and its modes as well as the issue of overcoming of Cartesian dualism. The author insists that cognitive scholars’ ambitions to overcome Cartesian dualism are vain. It is Descartes’ method and style - as far as we can grasp them - that can help to overcome fatal schemes ascribed into notorious mind - body problem. The core of Descartes’ thinking is the continuous preoccupation with embodiment of the rational and emotional aspects of his whole self (total me) and disembodiment of its material aspects.

Averaging combined with non-smooth unfolding transformations is used in this paper for investigating of the basic properties of an oscillator in a clearance. The classical stereo-mechanical approach is used in order to describe collisions between the mass and the limits. Energy dissipation during collision events is taken into account. The analysis is concentrated on the oscillation regimes with alternating collisions with both sides of the clearance. The self-excited friction oscillator in a clearance is considered as the first example. It is shown that applying the unfolding transformation the oscillator can be converted to an almost conservative pendulum rotating in a limited, non-smooth periodical potential field. Analytic predictions are obtained for the total energy of the pendulum which is the natural measure for the oscillations intensity. It is shown that the oscillation frequency can be controlled by changing the negative slope of the friction characteristics, by alternating the normal force and varying the length of the clearance. The classical externally excited oscillator in the clearance is considered as the second example. Applying the same approach the problem of the resonant oscillations can be reduces to the analysis of the rotation of the harmonically excited pendulum in the same potential field as in the first example. The main attention is paid to the high-energy resonances. The perturbation analysis in the vicinity of the resonant surfaces enables to dissociate slow, semi-slow and fast motions and to obtain very accurate analytic predictions for the energies of stationary resonant regimes. It is demonstrated that different high-energy regimes exist alongside with low-energy oscillations. The last case is typical for relative strong energy losses during collision events, so that the system needs several collision-free oscillations in order to increase the amplitude and reach the limits of the clearance.

Abstract We analyze the forced oscillations of an infinite string supported by an array of vibro-impact supports. The envelope of the excitation possesses ‘slow’ and ‘fast’ scales and is periodic with respect to the ‘fast’ scale. The ‘fast’ spatial scale is defined by the distance between adjacent nonlinear supports. To eliminate the singularities from the governing equations of motion that arise due to the discrete nature of the supports, we employ the nonsmooth transformations of the spatial variable first introduced in (Pilipchuk, 1985) and (Pilipchuk, 1988). Thus, we convert the problem to a set of two nonhomogeneous nonlinear boundary value problems which we solve by means of perturbation theory. The boundary conditions of these problems arise from ‘smoothness conditions’ that are imposed to guarantee sufficient differentiability of the results. The transformed system of equations is simplified using regular perturbation and harmonic balancing. Standing solitary wave solutions reflecting the discreteness effects inherent in the discrete foundation are calculated numerically for the unforced system.

In this paper, we present a novel method for multidimensional damage identification based on a dynamical systems approach to damage evolution. This approach does not depend on the knowledge of particular damage physics, and is appropriate for systems where damage evolves on much slower time scale then the directly observable dynamics. In an experimental context, the phase space reconstruction and locally linear models are used to quantify small distortions occurring in a dynamical system’s phase space due to damage accumulation. These measurements are then related to the drifts in damage variables. A mathematical model of a harmonically driven cantilever beam in a force field of two battery-powered electromagnets is used to demonstrate validity of the method. It is explicitly demonstrated that an affine projection of the described damage metric accurately tracks the two competing damage processes. For practical damage identification purposes, the tracking data is analyzed using the proper orthogonal decomposition (POD) and optimal tracking (OT) methods. Both methods correctly identify the two dominant damage modes. However, the OT is more impervious to changes in fast-time dynamics and provides a significantly better signal-to-noise ratio. The OT-based damage observer is demonstrated to be within a linear transformation from the actual damage states.