Active Isometric Contraction Research Articles

Phosphorylation of myosin regulatory light chain controls myosin head conformation in cardiac muscle

The effect of phosphorylation on the conformation of the regulatory light chain (cRLC) region of myosin in ventricular trabeculae from rat heart was determined by polarized fluorescence from thiophosphorylated cRLCs labelled with bifunctional sulforhodamine (BSR). Less than 5% of cRLCs were endogenously phosphorylated in this preparation, and similarly low values of basal cRLC phosphorylation were measured in fresh intact ventricle from both rat and mouse hearts. BSR-labelled cRLCs were thiophosphorylated by a recombinant fragment of human cardiac myosin light chain kinase, which was shown to phosphorylate cRLCs specifically at serine 15 in a calcium- and calmodulin-dependent manner, both in vitro and in situ. The BSR-cRLCs were exchanged into demembranated trabeculae, and polarized fluorescence intensities measured for each BSR-cRLC in relaxation, active isometric contraction and rigor were combined with RLC crystal structures to calculate the orientation distribution of the C-lobe of the cRLC in each state. Only two of the four C-lobe orientation populations seen during relaxation and active isometric contraction in the unphosphorylated state were present after cRLC phosphorylation. Thus cRLC phosphorylation alters the equilibrium between defined conformations of the cRLC regions of the myosin heads, rather than simply disordering the heads as assumed previously. cRLC phosphorylation also changes the orientation of the cRLC C-lobe in rigor conditions, showing that the orientation of this part of the myosin head is determined by its interaction with the thick filament even when the head is strongly bound to actin. These results suggest that cRLC phosphorylation controls the contractility of the heart by modulating the interaction of the cRLC region of the myosin heads with the thick filament backbone.

Age-related differences in strain rate tensor of the medial gastrocnemius muscle during passive plantarflexion and active isometric contraction using velocity encoded MR imaging: potential index of lateral force transmission.

The strain rate (SR) tensor measures the principal directions and magnitude of the instantaneous deformation; this study aims to track age-related changes in the 2D SR tensor in the medial gastrocnemius during passive joint rotation and active isometric contraction. SR tensors were derived from velocity encoded magnetic resonance phase-contrast images in nine young (28 years) and eight senior (78 years) women. Strain rates along and in the cross-section of the fiber were calculated from the SR tensor and used to derive the out-plane SR. Age-related and regional differences in the SR eigenvalues, orientation, and the angle between the SR and muscle fiber (SR-fiber angle) were statistically analyzed. SR along the fiber was significantly different between the cohorts during isometric contraction with higher values in the young (P < 0.05). The SR-fiber angle was larger in the young for both motion types but this difference was not statistically significant. Significant regional differences in the SR indices was seen in passive joint rotation (P < 0.05) for both cohorts. SR mapping reflects age-related and regional differences during active and passive motion respectively; this may arise from differences in contractility (active motion) and elastic properties (active and passive motion).

Sarcomere‐length dependence of myosin filament structure in skeletal muscle fibres of the frog

X-ray diffraction patterns were recorded at beamline ID02 of the European Synchrotron Radiation Facility from small bundles of skeletal muscle fibres from Rana esculenta at sarcomere lengths between 2.1 and 3.5μm at 4°C. The intensities of the X-ray reflections from resting fibres associated with the quasi-helical order of the myosin heads and myosin binding protein C (MyBP-C) decreased in the sarcomere length range 2.6-3.0μm but were constant outside it, suggesting that an OFF conformation of the thick filament is maintained by an interaction between MyBP-C and the thin filaments. During active isometric contraction the intensity of the M3 reflection from the regular repeat of the myosin heads along the filaments decreased in proportion to the overlap between thick and thin filaments, with no change in its interference fine structure. Thus, myosin heads in the regions of the thick filaments that do not overlap with thin filaments are highly disordered during isometric contraction, in contrast to their quasi-helical order at rest. Heads in the overlap region that belong to two-headed myosin molecules that are fully detached from actin are also highly disordered, in contrast to the detached partners of actin-attached heads. These results provide strong support for the concept of a regulatory structural transition in the thick filament involving changes in both the organisation of the myosin heads on its surface and the axial periodicity of the myosin tails in its backbone, mediated by an interaction between MyBP-C and the thin filaments.

Primary sensory and motor cortex activities during voluntary and passive ankle mobilization by the SHADE orthosis

This study investigates cortical involvement during ankle passive mobilization in healthy subjects, and is part of a pilot study on stroke patient rehabilitation. Magnetoencephalographic signals from the primary sensorimotor areas devoted to the lower limb were collected together with simultaneous electromyographic activities from tibialis anterior (TA). This was done bilaterally, on seven healthy subjects (aged 29 ± 7), during rest, left and right passive ankle dorsiflexion (imparted through the SHADE orthosis, O-PM, or neuromuscular electrical stimulation, NMES-PM), and during active isometric contraction (IC-AM). The effects of focussing attention on ankle passive movements were considered. Primary sensory (FS(S1)) and motor (FS(M1)) area activities were discriminated by the Functional Source Separation algorithm. Only contralateral FS(S1) was recruited by common peroneal nerve stimulation and only contralateral FS(M1) displayed coherence with TA muscular activity. FS(M1) showed higher power of gamma rhythms (33-90 Hz) than FS(S1). Both sources displayed higher beta (14-32 Hz) and gamma powers in the left than in the right hemisphere. Both sources displayed a bilateral reduction of beta power during IC-AM with respect to rest. Only FS(S1) beta band power reduced during O-PM. No beta band modulation was observed of either source during NMES-PM. Mutual FS(S1)-FS(M1) coherence in gamma2 band (61-90 Hz) showed a slight trend towards an increase when focussing attention during O-PM. Somatosensory and motor counterparts of lower limb cortical representations were discriminated in both hemispheres. SHADE was effective in generating repeatable dorsiflexion and inducing primary sensory involvement similarly to voluntary movement.

Primary sensory-motor cortex activity during voluntary and passive ankle mobilisation

Event Abstract Back to Event Primary sensory-motor cortex activity during voluntary and passive ankle mobilisation Filippo Zappasodi1*, Simone Pittaccio2, Stefano Viscuso2, Camillo Porcaro3, Francesca Mastrolilli4, Matilde Ercolani4, Francesco Passarelli4, Franco Molteni5, Stefano Besseghini2, Paolo M. Rossini6 and Franca Tecchio7 1 G. D Annunzio University, Department of Clinical Sciences and Bioimaging , Italy 2 CNR-IENI, Italy 3 BUIC, United Kingdom 4 Ospedale Fatebenefratelli, AFaR , Italy 5 Clinica Villa Beretta, Ospedale Valduce, Italy 6 ‘Campus Bio-Medico' University, Department of Neurology, Italy 7 Ospedale Fatebenefratelli, CNR-ISTC, Unità MEG, Italy This study investigates cortical involvement during ankle passive mobilisation in healthy subjects, and is part of a pilot study on stroke patient rehabilitation. Magnetoencephalographic signals from sensorimotor areas devoted to lower limb and tibialis anterior (TA) electromyographic activities were collected bilaterally and simultaneously on 7 healthy subjects during rest (Rest), left and right ankle dorsiflexion imparted through the SHADE orthosis (O-PM) or neuromuscular electrical stimulation (NMES-PM), or during active isometric contraction (IC-AM). The effects of focussing attention on ankle movements were considered. Primary sensory (FS_S1) and motor (FS_M1) area activities were discriminated by the Functional Source Separation algorithm. Power in alpha [8-12.5 Hz], beta [13-33 Hz], gamma1 [33-45 Hz] and gamma2 [60-90 Hz] bands of the sources and their coherence during each condition were calculated. Source band reactivity was evaluated as reduction of power with respect to Rest. Only contralateral FS_S1 was recruited by common peroneal nerve stimulation and only contralateral FS_M1 displayed coherence with TA muscular activity. FS_M1 showed higher power of gamma rhythms than FS_S1. Both sources reacted bilaterally during IC-AM in beta band. Only FS_S1 was also reactive during O-PM. No reactivity of either source resulted during NMES-PM. FS_S1-FS_M1 coherence was higher in gamma2 band when focussing attention only during O-PM, especially when using the right foot. Somatosensory and motor counterparts of lower limb cortical representations were discriminated in both hemispheres, and a prevalence of the left dominant hemisphere was evidenced. SHADE was effective in generating repeatable dorsiflexion and inducing primary sensory involvement similarly to voluntary movement. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Poster Presentation Topic: Sensory Processing and Functional Connectivity Citation: Zappasodi F, Pittaccio S, Viscuso S, Porcaro C, Mastrolilli F, Ercolani M, Passarelli F, Molteni F, Besseghini S, Rossini PM and Tecchio F (2010). Primary sensory-motor cortex activity during voluntary and passive ankle mobilisation. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00149 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Mar 2010; Published Online: 25 Mar 2010. * Correspondence: Filippo Zappasodi, G. D Annunzio University, Department of Clinical Sciences and Bioimaging, Chieti, Italy, f.zappasodi@unich.it Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Filippo Zappasodi Simone Pittaccio Stefano Viscuso Camillo Porcaro Francesca Mastrolilli Matilde Ercolani Francesco Passarelli Franco Molteni Stefano Besseghini Paolo M Rossini Franca Tecchio Google Filippo Zappasodi Simone Pittaccio Stefano Viscuso Camillo Porcaro Francesca Mastrolilli Matilde Ercolani Francesco Passarelli Franco Molteni Stefano Besseghini Paolo M Rossini Franca Tecchio Google Scholar Filippo Zappasodi Simone Pittaccio Stefano Viscuso Camillo Porcaro Francesca Mastrolilli Matilde Ercolani Francesco Passarelli Franco Molteni Stefano Besseghini Paolo M Rossini Franca Tecchio PubMed Filippo Zappasodi Simone Pittaccio Stefano Viscuso Camillo Porcaro Francesca Mastrolilli Matilde Ercolani Francesco Passarelli Franco Molteni Stefano Besseghini Paolo M Rossini Franca Tecchio Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. 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Structure‐Function Relation of the Myosin Motor in Striated Muscle

Force and shortening in striated muscle are driven by a structural working stroke in the globular portion of the myosin molecules-the myosin head-that cross-links the myosin-containing filaments and the actin-containing filaments. We use time-resolved X-ray diffraction in single fibers from frog skeletal muscle to link the conformational changes in the myosin head determined at atomic resolution in crystallographic studies with the kinetic and mechanical features of the molecular motor in the preserved sarcomeric structure. Our approach exploits the improved brightness and collimation of the X-ray beams of the third generation synchrotrons by using X-ray interference between the two arrays of myosin heads in each bipolar myosin filament to measure with A sensitivity the axial motions of myosin heads in situ during the synchronous execution of the working stroke elicited by rapid decreases in length or load imposed during an active isometric contraction. Changes in the intensity and interference-fine structure of the axial X-ray reflections following the mechanical perturbation allowed to establish the average conformation of the myosin heads during the active isometric contraction and the extent of tilt during the elastic response and during the subsequent working stroke. The myosin working stroke is 12 nm at low loads, which is consistent with crystallographic studies, while it is smaller and slower at higher loads. The load dependence of the size and speed of the myosin working stroke is the molecular determinant of the macroscopic performance and efficiency of muscle.

X-ray diffraction studies of the contractile mechanism in single muscle fibres

The molecular mechanism of muscle contraction was investigated in intact muscle fibres by X-ray diffraction. Changes in the intensities of the axial X-ray reflections produced by imposing rapid changes in fibre length establish the average conformation of the myosin heads during active isometric contraction, and show that the heads tilt during the elastic response to a change in fibre length and during the elementary force generating process: the working stroke. X-ray interference between the two arrays of myosin heads in each filament allows the axial motions of the heads following a sudden drop in force from the isometric level to be measured in situ with unprecedented precision. At low load, the average working stroke is 12 nm, which is consistent with crystallographic studies. The working stroke is smaller and slower at a higher load. The compliance of the actin and myosin filaments was also determined from the change in the axial spacings of the X-ray reflections following a force step, and shown to be responsible for most of the sarcomere compliance. The mechanical properties of the sarcomere depend on both the motor actions of the myosin heads and the compliance of the myosin and actin filaments.

Electron Tomography of Insect Flight Muscle in Isometric Contraction and Rigor States

Electron microscopy is a technology fully capable of bridging the light microscopic world with the world of protein structure at atomic resolution. There are numerous examples of cases where cryoelectron microscopy has been used to fit an atomic structure into a structure that has been difficult to crystallize for high resolution structure analysis. More difficult is the fitting of atomic structures into more conventionally prepared tissue like that used in freeze substitution.We have been using electron tomography to obtain 3-D images of insect flight muscle in various states, including those produced in an active isometric contraction as well as in rigor. These tomograms were obtained using non-uniform tilt angles, cross correlation alignment, area matching and Whittaker-Shannon interpolation of the 3-D transform. The fitting of atomic structures into raw tomograms is a difficult proposition because of the relatively highly noisy feature of the images. Better results are obtained when averages are produced. We have used two method for producing averages. One of these, the so-called column average is used when the muscle filaments are relatively straight with good axial order, or can be straightened in 3-D but their lateral ordering is poor. Column averaging improved considerably reduced the noise in tomograms of contracting muscle enabling the four major crossbridge conformation to be observed (Fig. 1).

The Effects of Acute Passive Stretch on Muscle Protein Synthesis in Humans

We examined the effect of an isolated bout of maximal tolerated passive stretch on fractional muscle protein synthetic rate in human soleus muscle. Eight healthy males performed two separate trials with the same leg: one session of passive stretch and one of intermittent active isometric contraction at a force equivalent to that which occurred during the passive stretch trial. This force was approximately 40% of maximum voluntary contraction force and produced volitional fatigue in approximately 27 min. Intermittent passive stretch, for the same duration, elicited a 6.1 degrees increase in joint angle (P<.0005) with silent electromyography. Fractional protein synthetic rate from experimental and control soleus in each trial was assessed from biopsy samples over the period 10-22 hr postexercise by the incorporation rate of L-[1-13C] leucine into muscle. Protein synthesis was elevated in the soleus of the exercised leg following the active contraction trial by 49% (P<.05) but not following the passive stretch trial. Results indicate that a single bout of maximal passive stretch does not significantly elevate fractional muscle protein synthetic rate in humans and thus suggests that muscle stretch per se is not the stimulus for the muscle hypertrophy that occurs with resistance training.

The Stiffness of Skeletal Muscle in Isometric Contraction and Rigor: The Fraction of Myosin Heads Bound to Actin

Step changes in length (between −3 and +5nm per half-sarcomere) were imposed on isolated muscle fibers at the plateau of an isometric tetanus (tension T0) and on the same fibers in rigor after permeabilization of the sarcolemma, to determine stiffness of the half-sarcomere in the two conditions. To identify the contribution of actin filaments to the total half-sarcomere compliance (C), measurements were made at sarcomere lengths between 2.00 and 2.15μm, where the number of myosin cross-bridges in the region of overlap between the myosin filament and the actin filament remains constant, and only the length of the nonoverlapped region of the actin filament changes with sarcomere length. At 2.1μm sarcomere length, C was 3.9nm T0−1 in active isometric contraction and 2.6nm T0−1 in rigor. The actin filament compliance, estimated from the slope of the relation between C and sarcomere length, was 2.3nm μm−1T0−1. Recent x-ray diffraction experiments suggest that the myosin filament compliance is 1.3nm μm−1T0−1. With these values for filament compliance, the difference in half-sarcomere compliance between isometric contraction and rigor indicates that the fraction of myosin cross-bridges attached to actin in isometric contraction is not larger than 0.43, assuming that cross-bridge elasticity is the same in isometric contraction and rigor.

Theory of light diffraction by single skeletal muscle fibers

A theoretical discussion is presented describing the diffraction of laser light by a single fiber of striated muscle. The complete three-dimensional geometry of the fiber has been taken into consideration. The basic repeated unit is taken as the sarcomere of a single myofibril, including its cylindrical geometry. The single fiber is considered as the sum of myofibrils up to the fiber dimensions. When proper phasing is taken into account, three cases of interest are analyzed. (a) When the adjacent myofibrils are totally aligned with respect to their index of refraction regions (e.g., A and I bands), then the diffraction pattern reflects that of a larger striated cylinder with the dimensions of the fiber. (b) When a particular skew plane develops for the myofibril elements, additional Bragg reflection occurs at certain specific sarcomere lengths, and intensity asymmetry amongst the diffracted orders occurs. (c) When the myofibril phasing changes in a random fashion, while all sarcomeres remain at the same length, then intensity decrease is directly related to the phase deviation from a reference phase point. This condition may well describe a fiber undergoing active isometric contraction.