Ipsi- and contralateral H-reflexes and V-waves after unilateral chronic Achilles tendon vibration

Chronic Achilles tendon vibration has previously shown its effectiveness in improving plantar flexor's strength and activation capacities. The present study investigated the related neural mechanisms by analyzing H-reflexes and V-waves of the soleus (SOL) and gastrocnemii (GM gastrocnemius medialis; GL gastrocnemius lateralis) muscles under maximal isometric plantar flexion. Moreover, recordings were conducted bilaterally to address potential crossed effects. 11 subjects were engaged in this study. Maximal voluntary contraction and superimposed H-reflexes and V-waves were quantified in both legs at baseline (PRE) and 2 weeks later to verify repeatability of data (CON). Then, subjects were retested after 14 days of daily unilateral Achilles tendon vibration (VIB; 1 h per day; frequency: 50 Hz). No changes were reported between PRE and CON data. In the VIB condition, there was an increase in MVC for both the vibrated (+9.1 %; p = 0.016) and non-vibrated (+10.2 %; p = 0.009) legs. The H-reflex increased by a mean 25 % in the vibrated SOL (p < 0.001), while it remained unchanged for the contralateral side (p = 0.531). The SOL V-wave also increased in the vibrated limb (+43.3 %; p < 0.001), as well as in the non-vibrated one (+41.9 %; p = 0.006). Furthermore, the GM V-wave increased by 37.8 % (p = 0.081) in the vibrated side and by 39.4 % (p = 0.03) in the non-vibrated side. However, no changes were reported for the GL muscles. While the present study confirmed the strength gains induced by chronic Achilles tendon vibration, the results indicated a cross-education phenomenon with differences in neural adaptations between the vibrated leg and non-vibrated leg.

Aggregation of the salivary proline-rich protein IB5 in the presence of the tannin EgCG

In the mouth, proline-rich proteins (PRP), which are major components of stimulated saliva, interact with tannins contained in food. We report in vitro interactions of the tannin epigallocatechin gallate (EgCG), with a basic salivary PRP, IB5, studied through electrospray ionization mass spectrometry (ESI-MS), small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS). In dilute protein (IB5) solutions of low ionic strength (1 mM), the proteins repel each other, and the tannins bind to nonaggregated proteins. ESI-MS experiments determine the populations of nonaggregated proteins that have bound various numbers of tannin molecules. These populations match approximately the Poisson distribution for binding to n = 8 sites on the protein. MS/MS experiments confirm that complexes containing n = 1 to 8 EgCG molecules are dissociated with the same energy. Assuming that the 8 sites are equivalent, we calculate a binding isotherm, with a binding free energy Δμ = 7.26RT(a) (K(d) = 706 μM). In protein solutions that are more concentrated (0.21 mM) and at higher ionic strength (50 mM, pH 5.5), the tannins can bridge the proteins together. DLS experiments measure the number of proteins per aggregate. This number rises rapidly when the EgCG concentration exceeds a threshold (0.2 mM EgCG for 0.21 mM of IB5). SAXS experiments indicate that the aggregates have a core-corona structure. The core contains proteins that have bound at least 3 tannins and the corona has proteins with fewer bound tannins. These aggregates coexist with nonaggregated proteins. Increasing the tannin concentration beyond the threshold causes the transfer of proteins to the aggregates and a fast rise of the number of proteins per aggregate. A poisoned growth model explains this fast rise. Very large cationic aggregates, containing up to 10,000 proteins, are formed at tannin concentrations (2 mM) slightly above the aggregation threshold (0.2 mM).

Influence of overweight on the active and the passive fraction of the plantar flexors series elastic component in prepubertal children

The influence of overweight, as a precursor to obesity, was analyzed on the elastic properties of the triceps surae. Based on body mass index (BMI), children (9 years ± 4 mo) were classified as control (CON; n = 23; BMI -1SD>Z score<1SD) or overweight (OW; n = 21, BMI 1SD>Z score<3SD) with regard to reference data from the World Health Organization. Musculotendinous (MT) stiffness of the series elastic component (SEC) was determined using quick-release tests to obtain 1) the MT stiffness index from the slope of either linear stiffness-torque (SI(MT-Torque)) or stiffness-EMG (SI(MT-EMG)) relationships and 2) passive stiffness from the intercept point with the ordinate. Finally, the SEC active (α(0)) and passive fractions (C(passive)) were separated as described by Morgan (Am J Physiol, 1977), using alpha-torque (α(0-Torque,) C(passive-Torque)) or alpha-EMG (α(0-EMG,) C(passive-EMG)) relationships. No significant differences in SI(MT-Torque) or α(0-Torque) were observed between OW and CON. SI(MT-EMG) or α(0-EMG) values were significantly different between OW and CON, which indicate an increase in MT stiffness. In all cases, passive stiffness (K(p), C(passive-torque), C(passive-EMG)) was significantly greater in OW but independent of the activation capacities. These results indicate that a weight-related additional loading of the MT structures in OW children caused the MT system to response accordingly to the functional demand, i.e., higher stiffness of the MT structures due to a concomitant increase in the stiffness of the SEC passive and active fraction. This study also reveals that possible differences in the activation capacities influence the determination of MT stiffness of the SEC active fraction.

Gas-Phase Protein Inner-Shell Spectroscopy by Coupling an Ion Trap with a Soft X-ray Beamline

C, N, and O near-edge ion yield spectroscopy of 8+ selected electrosprayed cations of cytochrome c protein (12 kDa) has been performed by coupling a linear quadrupole ion trap with a soft X-ray beamline. The photoactivation tandem mass spectra were recorded as a function of the photon energy. Photoionization of the precursor, accompanied by CO2 loss, is the dominant relaxation process, showing high photoion stability following direct or resonant photoionization. The partial ion yields extracted from recorded mass spectra show significantly different behaviors for single and double ionization channels, which can be qualitatively explained by different Auger decay mechanisms. However, the single ionization spectra reveal characteristic structures when compared to existing near-edge X-ray absorption fine structure (NEXAFS) spectra from thin films of peptides and proteins. Therefore, the present experiment opens up new avenues for near-edge X-ray spectroscopy of macromolecules in the gas phase, overcoming the radiation damage issue or the environmental effects as due to the surface, intermolecular interactions, and solvent.

VUV synchrotron radiation: a new activation technique for tandem mass spectrometry

A novel experimental technique for tandem mass spectrometry and ion spectroscopy of electrosprayed ions using vacuum-ultraviolet (VUV) synchrotron radiation is presented. Photon activation of trapped precursor ions has been performed by coupling a commercial linear quadrupole ion trap (Thermo scientific LTQ XL), equipped with the electrosprayed ions source, to the DESIRS beamline at the SOLEIL synchrotron radiation facility. The obtained results include, for the first time on biopolymers, photodetachment spectroscopy using monochromated synchrotron radiation of multi-charged anions and the single photon ionization of large charge-selected polycations. The high efficiency and signal-to-noise ratio achieved by the present set-up open up possibilities of using synchrotron light as a new controllable activation method in tandem mass spectrometry of biopolymers and VUV-photon spectroscopy of large biological ions.

Formation and fragmentation of radical peptide anions: insights from vacuum ultra violet spectroscopy

We have studied the photodissociation of gas-phase deprotonated caerulein anions by vacuum ultraviolet (VUV) photons in the 4.5 to 20 eV range, as provided by the DESIRS beamline at the synchrotron radiation facility SOLEIL (France). Caerulein is a sulphated peptide with three aromatic residues and nine amide bonds. Electron loss is found to be the major relaxation channel at every photon energy. However, an increase in the fragmentation efficiency (neutral losses and peptide backbone cleavages) as a function of the energy is also observed. The oxidized ions, generated by electron photodetachment were further isolated and activated by collision (CID) in a MS(3) scheme. The branching ratios of the different fragments observed by CID as a function of the initial VUV photon energy are found to be independent of the initial photon energy. Thus, there is no memory effect of the initial excitation energy on the fragmentation channels of the oxidized species on the time scale of our tandem MS experiment. We also report photofragment yields as a function of photon energy for doubly deprotonated caerulein ions, for both closed-shell ([M-2H](2-)) non-radical ions and open-shell ([M-3H](2-•)) radical ions. These latter ions are generated by electron photodetachment from [M-3H](3-) precursor ions. The detachment yield increases monotonically with the energy with the appearance of several absorption bands. Spectra for radical and non-radical ions are quite similar in terms of observed bands; however, the VUV fragmentation yield is enhanced by the presence of a radical in caerulein peptides.

Separation of peptides from detergents using ion mobility spectrometry

Mass spectrometry (MS) has dramatically evolved in the last two decades and has been the driving force of the spectacular expansion of proteomics during this period. However, the very poor compatibility of MS with detergents is still a technical obstacle in some studies, in particular on membrane proteins. Indeed, the high hydrophobicity of membrane proteins necessitates the use of detergents for their extraction and solubilization. Here, we address the analytical potential of high-field asymmetric waveform ion mobility spectrometry (FAIMS) for separating peptides from detergents. The study was focused on peptides from the human integral membrane protein CD9. A tryptic peptide was mixed with the non-ionic detergents Triton X-100 or beta-D-dodecyl maltoside (DDM) as well as with the ionic detergents sodium dodecyl sulfate (SDS) or sodium deoxycholate (SDC). Although electrospray ionization (ESI) alone led to a total suppression of the peptide ion signal on mass spectra with only detection of the detergents, use of FAIMS allowed separation and clear identification of the peptide with any of the detergents studied. The detection and identification of the target compound in the presence of an excess of detergents are then feasible. FAIMS should prove especially useful in the structural and proteomic analysis of membrane proteins.

Gas phase photo-formation and vacuum UV photofragmentation spectroscopy of tryptophan and tyrosine radical-containing peptides

Tryptophan (Trp(•)) and tyrosyl (Tyr(•)) radical containing peptides were produced by UV laser-induced electron detachment from a suitable precursor. Vacuum ultraviolet (VUV) action spectra of these radical peptides were recorded with synchrotron radiation in the 4.5-16 eV range, from which fragmentation pathways and yields are measured as a function of the VUV photon energy. An enhancement in photofragmentation yields of radical species by 1 order of magnitude with respect to nonradical peptides is demonstrated here for the first time. Photofragmentation spectra are compared with absorption spectra for model chromophores calculated in the frame of the time-dependent density functional theory (TDDFT). A qualitative agreement in the position of bands in the 6-8 eV region is observed between experimental photofragmentation and calculated absorption spectra. Photofragmentation spectra of peptide radicals can be useful to better assess the complex deactivation pathways that occur following the absorption of a VUV photon in biomolecular radical anions.

Proline-rich salivary proteins have extended conformations

Three basic proline-rich salivary proteins have been produced through the recombinant route. IB5 is a small basic proline-rich protein that is involved in the binding of plant tannins in the oral cavity. II-1 is a larger protein with a closely related backbone; it is glycosylated, and it is also able to bind plant tannins. II-1 ng has the same polypeptidic backbone as II-1, but it is not glycosylated. Small angle x-ray scattering experiments on dilute solutions of these proteins confirm that they are intrinsically disordered. IB5 and II-1 ng can be described through a chain model including a persistence length and cross section. The measured radii of gyration (Rg=27.9 and 41.0+/-1 A respectively) and largest distances (rmax=110 and 155+/-10 A respectively) show that their average conformations are rather extended. The length of the statistical segment (twice the persistence length) is b=30 A, which is larger than the usual value (18 A-20 A) for unstructured polypeptide chains. These characteristics are presumably related to the presence of polyproline helices within the polypeptidic backbones. For both proteins, the radius of gyration of the chain cross-section is Rc=2.7+/-0.2A. The glycosylated protein II-1 has similar conformations but the presence of large polyoside sidegroups yields the structure of a branched macromolecule with the same hydrophobic backbone and hydrophilic branches. It is proposed that the unusually extended conformations of these proteins in solution facilitate the capture of plant tannins in the oral cavity.

The hidden face of food phenolic composition

Plant polyphenols are extremely diverse, due to the occurrence of several basic structures, numerous substitutions and, for some groups, of polymers (tannins). Plant polyphenol composition depends on the plant species and organ, with some molecules specific of particular plant families while others are ubiquitous. The polyphenol content is classically assessed by global analysis methods, which lack specificity and accuracy. These methods have been replaced with high performance liquid chromatography (HPLC), that enables accurate determination of individual molecules, provided they can be unambiguously identified and calibration curves can be established. However, HPLC analysis is restricted to simple compounds and difficult to apply in the case of complex extracts. Further difficulties encountered in the case of polymers include irreversible adsorption on the stationary phases. Proanthocyanidin analysis by HPLC after acid-catalysed depolymerisation in the presence of a nucleophile permits to overcome these problems and shows that proanthocyanidins predominate in the polyphenol composition of most plants. Large varietal differences in tannin quantitative and qualitative composition were observed for all plant species studied. Moreover, analysis is usually performed after extraction, which may lead to significant underestimation of the polyphenol content, since a large proportion is not extracted by usual solvents. This may be due to covalent binding to other plant constituents and to non-covalent adsorption on plant solids. Such matrix effect also influences the taste perception of polyphenols and their fate in the digestive tract, from in-mouth interactions with salivary proteins to their metabolism by colon microflora, with potential influence on bioavailability.

Accelerated Achilles tendon healing by PDGF gene delivery with mesoporous silica nanoparticles

We report the ability of amino- and carboxyl-modified MCM-41 mesoporous silica nanoparticles (MSN) to deliver gene in vivo in rat Achilles tendons, despite their inefficiency to transfect primary tenocytes in culture. We show that luciferase activity lasted for at least 2 weeks in tendons injected with these MSN and a plasmid DNA (pDNA) encoding the luciferase reporter gene. By contrast, in tendons injected with naked plasmid, the luciferase expression decreased as a function of time and became hardly detectable after 2 weeks. Interestingly, there were neither signs of inflammation nor necrosis in tendon, kidney, heart and liver of rat weekly injected with pDNA/MSN formulation during 1.5 months. Our main data concern the acceleration of Achilles tendons healing by PDGF-B gene transfer using MSN. Biomechanical properties and histological analyses clearly indicate that tendons treated with MSN and PDGF gene healed significantly faster than untreated tendons and those treated with pPDGF alone.

Passive stiffness of rat skeletal muscle undernourished during fetal development

OBJECTIVES

The aim of the study was to investigate the effect of fetal undernutrition on the passive mechanical properties of skeletal muscle of weaned and young adult rats.

INTRODUCTION

A poor nutrition supply during fetal development affects physiological functions of the fetus. From a mechanical point of view, skeletal muscle can be also characterized by its resistance to passive stretch.

METHODS

Male Wistar rats were divided into two groups according to their mother's diet during pregnancy: a control group (mothers fed a 17% protein diet) and an isocaloric low-protein group (mothers fed a 7.8% protein diet). At birth, all mothers received a standardized meal ad libitum. At the age of 25 and 90 days, the soleus muscle and extensor digitorum longus (EDL) muscles were removed in order to test the passive mechanical properties. A first mechanical test consisted of an incremental stepwise extension test using fast velocity stretching (500 mm/s) enabling us to measure, for each extension stepwise, the dynamic stress (σd) and the steady stress (σs). A second test consisted of a slow velocity stretch in order to calculate normalized stiffness and tangent modulus from the stress-strain relationship.

RESULTS

The results for the mechanical properties showed an important increase in passive stiffness in both the soleus and EDL muscles in weaned rat. In contrast, no modification was observed in young adult rats.

CONCLUSIONS

The increase in passive stiffness in skeletal muscle of weaned rat submitted to intrauterine undernutrition it is most likely due to changes in muscle passive stiffness.

A regional model (Northeastern Brazil) of induced mal-nutrition delays ontogeny of reflexes and locomotor activity in rats

The aim of this study was to investigate the effects of malnutrition, induced by a regional basic diet (RBD), on motor development. RBD is a 7.87%-protein diet based on aliments typical of Northeastern Brazil, elaborated after nutritional investigation by Teodosio et al. (1979). Female rats were treated with RBD during lactation. The reflex ontogenesis and the development of locomotor activity in their offspring were assessed. Malnourished (MN) rats showed a delay in reflex maturation and in locomotor activity evolution. The decreased locomotor activity may be related to the reduced movement experiences induced by the delay in the reflex maturation. Occurring during the critical period of brain development, this fact could jeopardize all the steps in future locomotion evolution. The present results confirm deleterious effects of RDB-induced malnutrition on the somatic development and maturation of the nervous system (NS).

Effects of chronic low frequency stimulation on contractile and elastic properties of hindlimb suspended rat soleus muscle

Chronic low frequency stimulation (10 Hz, 8 h x day[-1]) was used in this study to prevent the changes in the contractile and elastic properties of rat soleus muscles induced by 3 weeks of hindlimb suspension (HS). Results showed that electrostimulation was able to counteract in part the decrease in soleus muscle mass and tension output induced by unweighting. On the other hand, the increases in maximal shortening velocity and twitch speed following HS were not prevented by stimulation. Unweighting was responsible for an increase in series elastic compliance of soleus muscle. Chronic stimulation successfully counteracted this increase in series compliance probably by changing the properties of the tendon. The partial recovery of muscle mass and tension output as a result of stimulation enhanced the role of contractile activity in preventing muscle atrophy. Moreover, the inefficiency of the tonic activity imposed by stimulation in preventing the increase in twitch speed of soleus muscle during HS demonstrated the primacy of neuronal activity. Discrepant results concerning changes in contraction kinetics deduced from the twitch could have been due to the fact that such myograms also depend on the series compliance.

Electrical stimulation of leg muscles increases tibial trabecular bone formation in unloaded rats

Rat head-down hindlimb suspension (HS) has been shown to induce hindlimb cancellous bone loss. As HS is known to associate unloading with progressive disappearance of hindlimb muscle contractions, we investigated whether persisting muscle motion could modify suspension-induced bone disorders or even prevent them. Chronic electrical stimulation (ES) was applied to leg muscles of rats during 3-wk hindlimb suspension, the lack of support for hindlimbs maintaining a hypodynamic situation. The histomorphometric characteristics of the proximal tibial metaphysis were analyzed. At the end of this protocol of combined suspension and stimulation, trabecular bone loss remained similar to that of nonstimulated HS animals. However, trabecular bone cell activity parameters showed greater bone formation after muscle stimulation in unloaded animals, with significantly increased osteoblastic, osteoid, and mineralizing surfaces. In addition, periosteal mineral apposition rate and cancellous bone formation rate, markedly decreased by suspension, were not significantly different in suspended stimulated compared with normal loaded animals. This enhanced formation activity could be related to persistence of muscle activity, as shown by partial preservation of muscle mass. However, direct electrical effects on bone cannot be excluded. Thus, despite muscle stimulation, with enhanced bone formation, isolated suppression of hypokinesia has not been able to counteract bone effects of unloading. This finding supports the hypothesis of the importance of mechanical loading to maintain bone architecture.

Changes in stiffness induced by hindlimb suspension in rat soleus muscle

Soleus muscle atrophy was induced by hind-limb suspension of rats for 3 weeks with the intention of inducing a relative increase in the percentage of fast-twitch fibres and assessing modifications in muscle stiffness. A method of dual controlled releases was used to obtain tension/extension curves and force/velocity relationships characterizing the mechanical behaviour of the soleus. Fibre typing was achieved by myofibrillar adenosine 5'-triphosphatase staining. Results showed that hindlimb suspension decreased the percentage of slow-twitch fibres (-31%) to the profit of fast-twitch fibres (+370%) and intermediate fibres (+255%). This led to an increase in maximal shortening velocity. Tension/extension curves indicated a decrease in soleus stiffness after 3 weeks of unloading. Changes in elastic properties are interpreted in terms of modifications occurring in the active part and the passive part of the so-called series elastic component. These changes also suggest that the parameters derived from a twitch are inappropriate to account for modifications in speed-related properties of muscle.

Assessment of physical activity in daily life

The absence of physical activity represents a major risk factor for coronary heart disease. Therefore, the evaluation of physical activity is a very current topic within the framework of epidemiologic studies. The aim of this study, based on the Baecke questionnaire, was to compare the various indices [leisure time activity index (LAI) and sport activity index (SAI)] obtained in a control population (control group) with those obtained in a population presenting risks of coronary disease [cardiovascular risk factor (CVRF)]. The control group consisted of 195 volunteers and the CVRF group of 69. All volunteers were between 27 and 60 years of age and had similar professional activities; therefore, the occupation activity index (OAI) evaluated in the original Baecke questionnaire was not taken into account. Maximal oxygen consumption (VO2max) was calculated for each volunteer using the indirect method involving shuttle run tests. The results have shown a direct correlation between SAI and VO2max in the control group (r = 0.309; p < 0.01), whereas VO2max did not appear to be correlated with the SAI in the CVRF group. This is probably because the VO2max value is underestimated. The use of indirect methods in populations presenting risk factors for coronary disease may be inappropriate, as the psychological attitude of the volunteers towards physical activity must be taken into account. Multiple regression analyses revealed that in both groups, 30% of the VO2max variations could be predicted by parallel variations in the mass of body fat and of the SAI, although the influence of these parameters is different in the two study groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of protein supplementation during prolonged exercise at moderate altitude on performance and plasma amino acid pattern

The effects of two levels of protein intake on muscle performance and energy metabolism were studied in humans submitted to repeated daily sessions of prolonged exercise at moderate altitude. For this purpose, 29 healthy males, were exposed to seven successive stages of ski-mountaineering at altitudes between 2500 and 3800 m, and to an isocaloric diet (4000 kcal.day-1, 16,760 kJ.day-1) with either 1.5 g.kg-1.day-1 (C group, n = 14), or 2.5 g.kg-1.day-1 (PR group, n = 15) protein intake. Measurements made after the ski-mountaineering programme did not show any change in body mass. The peak torque during maximal isometric voluntary contraction (MVC) of the quadriceps muscle was unaffected by the repeated exercises, whereas the endurance time at 50% MVC was decreased in PR subjects (-26.8%, P < 0.001). Increased levels of both free fatty acids (+ 147%, P < 0.001) and glycerol (+ 170%, P < 0.001) observed in C subjects would suggest that lipolysis was enhanced after the repeated exercise. The plasma amino acid pattern was altered after completion of the ski-mountaineering programme; the plasma concentration of the three branched-chain amino acids (BCAA) was significantly decreased in C subjects, whereas the higher level of protein intake (PR group) greatly minimized the exercise-induced decrease in serum BCAA.