Isotope effect and multiscale physics in fusion plasmas.

The mechanism governing the impact of the mass isotope on plasma confinement is still one of the main scientific conundrums facing the magnetic fusion community after more than thirty years of intense research. We have investigated the properties of local turbulence and long-range correlations in hydrogen and deuterium plasmas in the TEXTOR tokamak. Experimental findings have shown a systematic increasing in the amplitude of long-range correlations during the transition from hydrogen to deuterium dominated plasmas. These results provide the first direct experimental evidence of the importance of multiscale physics for unraveling the physics of the isotope effect in fusion plasmas.

The upgraded TOMAS device: A toroidal plasma facility for wall conditioning, plasma production, and plasma-surface interaction studies.

The Toroidal Magnetized System device has been significantly upgraded to enable development of various wall conditioning techniques, including methods based on ion and electron cyclotron (IC/EC) range of frequency plasmas, and to complement plasma-wall interaction research in tokamaks and stellarators. The toroidal magnetic field generated by 16 coils can reach its maximum of 125 mT on the toroidal axis. The EC system is operated at 2.45 GHz with up to 6 kW forward power. The IC system can couple up to 6 kW in the frequency range of 10 MHz-50 MHz. The direct current glow discharge system is based on a graphite anode with a maximum voltage of 1.5 kV and a current of 6 A. A load-lock system with a vertical manipulator allows exposure of material samples. A number of diagnostics have been installed: single- and triple-pin Langmuir probes for radial plasma profiles, a time-of-flight neutral particle analyzer capable of detecting neutrals in the energy range of 10 eV-1000 eV, and a quadrupole mass spectrometer and video systems for plasma imaging. The majority of systems and diagnostics are controlled by the Siemens SIMATIC S7 system, which also provides safety interlocks.

A case-based, small-group cooperative learning course in preclinical veterinary science aimed at bridging basic science and clinical literacy.

In 1999 a dedicated problem-based learning course was introduced into the lecture-based preclinical veterinary curriculum of the University of Pretoria. The Introduction to Clinical Studies Course combines traditional lectures, practical sessions, student self-learning and guided tutorials. The self-directed component of the course utilises case-based, small-group cooperative learning as an educational vehicle to link basic science with clinical medicine. The aim of this article is to describe the objectives and structure of the course and to report the results of the assessment of the students' perceptions on some aspects of the course. Students reacted very positively to the ability of the course to equip them with problem-solving skills. Students indicated positive perceptions about the workload of the course. There were, however, significantly lower scores for the clarity of the course objectives. Although the study guide for the course is very comprehensive, the practice regarding the objectives is still uncertain. It is imperative to set clear objectives in non-traditional, student-centred courses. The objectives have to be explained at the outset and reiterated throughout the course. Tutors should also communicate the rationale behind problem-based learning as a pedagogical method to the students. Further research is needed to verify the effectiveness of this course in bridging the gap between basic science and clinical literacy in veterinary science. Ongoing feedback and assessment of the management and content are important to refine this model for integrating basic science with clinical literacy.

C-reactive protein in canine babesiosis caused by Babesia rossi and its association with outcome.

C-reactive protein (CRP) is a positive major acute-phase protein in dogs and can be used as a predictive marker for risk of disease and to monitor the response to treatment. Increased concentrations in certain diseases are associated with poor outcome. This cross-sectional, observational study of 75 dogs naturally infected with Babesia rossi was designed to examine the relationship between outcome and CRP concentration at admission and the magnitude of CRP change 24 hours after admission. Diagnosis was confirmed by polymerase chain reaction (PCR) and reverse line blot. CRP concentrations were determined by an automated human CRP Turbidometric Immunoassay, previously validated for use in dogs. There was no significant difference in mean CRP concentration between survivors (n = 57), 107.5 +/- 49.5 mg/l and non-survivors (n = 11), 122.1 +/- 64.6 mg/l at admission and using the exact logistic regression, adjusting for age and sex, there was no association with outcome (P = 0.53). Multiple regression analysis failed to show a significant relationship between admission CRP concentration and number of days of hospitalisation in the survivors, adjusting for age and sex (P = 0.65). Similarly, no significance was found in the relationship between the magnitude of change in CRP concentration 24 hours after admission, and the number of days of hospitalisation in survivors, (P = 0.34). It is concluded that CRP concentration, as a measure of the acute phase response, is not associated with outcome in canine babesiosis, and inflammation is unlikely to be the only cause of severity of disease.

Involvement of trp-2 protein in store-operated influx of calcium in fibroblasts.

Mammalian homologues of the Drosophila melanogaster transient receptor potential (trp) gene have been proposed to encode store-operated channels. This assertion essentially stays on the fact that expression of different trp proteins produces trans-membrane cation currents. However, the selectivity of the expressed channels and their mode of activation, in particular, their dependence to store depletion appears to be quite variable. In the present work, we adopted an anti-sense strategy to study this question in transfected Chinese hamster ovary cells expressing the rat neurotensin receptor (CHO-NTR cells), a cellular model characterized by its very large store-dependent entry of Ca(2+). We identified different trp transcripts by RT-PCR, the trp-1 and trp-2 transcripts being by far the most abundant. CHO-NTR cells were then transfected with a mouse trp-2 anti-sense construct (CHO-NTR-TRP2AS cells). We showed that in these cells, trp-2 mRNA was suppressed in comparison with cells transfected with a control plasmid. The store-operated entry of Ca(2+) was evaluated after store depletion by an IP(3)-dependent mechanism (neurotensin stimulation) or by direct inhibition of the endoplasmic reticulum Ca(2+)ATPase (thapsigargin stimulation). In both cases, store-dependent entry of Ca(2+) was largely reduced in CHO-NTR-TRP2AS cells in comparison with control cells, suggesting that trp-2 protein might constitute a functional subunit of store-operated channels.

Intracellular pH regulation in isolated fast-twitch skeletal muscle from dystrophin-deficient mouse.

In muscles from anaesthetized dystrophin-deficient mdx mice, exercise results in a stronger acidification and a slower intracellular pH recovery compared to control mice. We examined whether this observation could be attributed to defective H+-carriers in dystrophin-lacking muscles. Immunohistochemistry and Western blots revealed no defect in mdx muscles for the presence of the lactate-/H+co-transporter MCT4 and of the Na+/H+ antiporter NHE1, the main H+-carriers active in fast-twitch skeletal muscle after exercise. Functional tests of the H+-transporters, on isolated muscles submitted to identical flow of superfusion, were performed in conditions meant to lower intracellular pH: repetitive electrical stimulation or NH4Cl pre-pulse. These revealed no defect in intracellular pH recovery in mdx muscles. Therefore, we conclude that impaired intracellular pH regulation in anaesthetized mdx mice is not attributable to a reduced presence or activity of H+-extruders. We propose that CO2 washout might be slowed down in vivo in mdx muscles because of the defective vascular response in contracting muscles from these mice.

Consequence of parvalbumin deficiency in the mdx mouse: histological, biochemical and mechanical phenotype of a new double mutant.

We tested the hypothesis whether the mild dystrophy in mdx mice could result from the contribution of the cytosolic calcium buffer parvalbumin in maintaining a normal cytosolic [Ca2+]i, in spite of an increased passive Ca2+ influx. By crossing mdx mice with parvalbumin-deficient mice, double mutant mice, lacking both dystrophin and parvalbumin, were obtained. Though resting cytosolic [Ca2+]i and total calcium content were similar to that of mdx muscles, this new animal model presented a slightly more severe phenotype than the mdx mouse. Muscle pseudo-hypertrophy, the density of myotubes and of centronucleated fibres as well as the loss of IIB fibres were all increased in parvalbumin-deficient mdx mice. Many of these deficits were overcome in late adulthood, albeit fibrosis was clearly more pronounced than in mdx muscles. At 90 days, parvalbumin-deficient mdx mice showed higher levels of creatine phosphokinase and lower muscle strength, in vivo, than mdx mice. Isometric tension of isolated muscle was reduced, but the susceptibility to eccentric contraction was not increased. The slight aggravation of muscle dystrophy observed in mdx mice deprived of parvalbumin cannot explain the severity of the affection observed in xmd dogs and Duchenne dystrophy patients where parvalbumin is constitutively not expressed.

Development of the gas-puff imaging diagnostic in the TEXTOR tokamak.

Gas puff imaging (GPI) [S. J. Zweben, D. P. Stotler et al., Phys. Plasmas 9, 1981 (2002); R. J. Maqueda, G. A. Wurden et al., Rev. Sci. Instrum. 74, 2020 (2003)] is a powerful diagnostic that permits a two-dimensional measurement of turbulence in the edge region of a fusion plasma and is based on the observation of the local emission of a neutral gas, actively puffed into the periphery of the plasma. The developed in-vessel GPI telescope observes the emission from the puffed gas along local (at the puff) magnetic field lines. The GPI telescope is specially designed to operate in severe TEXTOR conditions and can be treated as a prototype for the GPI systems on next generation machines. Also, the gas puff nozzle is designed to have a lower divergence of the gas flow than previous GPI diagnostics. The resulting images show poloidally and radially propagating structures, which are associated with plasma blobs. We demonstrate that the local gas puff does not disturb plasma properties. Our results indicate also that the neutral gas emission intensity is more sensitive to the electron density than the electron temperature. Here, we present implementation details of the GPI system on TEXTOR and discuss some design and diagnostic issues related to the development of GPI systems in general.

In situ measurements of calpain activity in isolated muscle fibres from normal and dystrophin-lacking mdx mice.

Calpains are Ca(2+)-activated proteases that are thought to be involved in muscle degenerative diseases such as Duchenne muscular dystrophy. Status and activity of calpains in adult muscle fibres are poorly documented. We report here in situ measurements of calpain activity in collagenase-isolated fibres from C57 mice and form two models of dystrophy: dystrophin-deficient mdx and calpain-3 knocked-out mice. Calpain activity was measured using a permeant, fluorogenic substrate and its Ca(2+) dependence was studied. A 30-fold change of activity was observed between the lowest and the highest steady-state Ca(2+) availability. Fast transient changes of [Ca(2+)](i) induced by electrical stimulation or KCl-dependent depolarization were ineffective in activating calpain. Slow [Ca(2+)] transients, as elicited during depletion of Ca(2+) stores, Ca(2+) store repletion and hypo-osmotic swelling were able to activate calpain. On return to resting conditions, calpain activity recovered its basal rate within 10 min. In resting intact muscle, mu-calpain was predominantly in the 80 kDa native form, with a small fraction in the 78 kDa autolysed form. The latter is thought to be responsible for the activity measured in our conditions. Calpain activity in mdx fibres showed an average 1.5-fold increase compared to activity in C57 fibres. This activity was reduced by a 10-fold lowering of [Ca(2+)](o). Calpain-3-deficient fibres showed about the same increase, thus calpain-3 did not contribute to the activity measured here and calpain activation is not specific to dystrophin deficiency. In fibres from transgenic mice over-expressing calpastatin, a 40-50% reduction of calpain activity was observed, as with synthetic drugs (Z-Leu-Leu-CHO and SNT198438). We provide novel information on the physiological factors that control calpain activity in situ, particularly the effect of intracellular Ca(2+) transients that occur in excitation-contraction coupling, Ca(2+) store depletion and refilling, and activation of mechanosensitive Ca(2+) channels.

Influence of the static Dynamic Ergodic Divertor on edge turbulence properties in TEXTOR.

Systematic measurements on the edge turbulence and turbulent transport have been made by Langmuir probe arrays on TEXTOR under various static Dynamic Ergodic Divertor (DED) configurations. Common features are observed. With the DED, in the ergodic zone the local turbulent flux reverses sign from radially outwards to inwards. The turbulence properties are profoundly modified by energy redistribution in frequency spectra and suppression of large scale eddies. The fluctuation poloidal phase velocity changes direction from electron to ion diamagnetic drift, consistent with the observed reversal of the Er x B flow. In the laminar region, the turbulence is found to react to an observed reduced flow shear.

Implantation of autologous cells in minced and devitalized rat skeletal muscles.

Triceps surae of 3 week-old female Wistar rats were minced and orthotopically autografted. Thirty days later, the regenerates developed a force of 314 +/- 58 mN during an isometric maximal tetanus and the maximal area of the muscle tissue was 3.2 +/- 0.5 mm2 (n = 9) in a cross-section. At 60 days, their mean maximal isometric force was increased (1159 +/- 367 mN) as also were their maximal muscle cross-section area (6.8 +/- 0.7 mm2;n = 6). If the minces were devitalized by a freeze and thaw procedure, the regenerates neither contracted under electrical stimulation nor contained any muscle fibre. If devitalized minces were seeded with myogenic cells isolated from the contralateral triceps surae, orthotopically autografted and allowed to regenerate for 30 days, the regeneration was weak: 46 +/- 14 mN of force, 1.2 +/- 0.3 mm2 of muscle area in minces devitalized by cold (n = 7) and 23 +/- 8 mN of force, 0.2 +/- 0.1 mm2 of muscle area in minces devitalized by cold supplemented by heat (n = 8). If viable minces were seeded with myogenic cells, there was no improvement in the extent of regeneration: 275 +/- 83 mN of force, 2.0 +/- 0.6 mm2 of muscle area at 30 days (n = 7) and 738 +/- 191 mN of force, 5.6 +/- 0.9 mm2 of muscle area at 60 days (n = 5). Consequently, although it is possible to induce regeneration by grafting myogenic cells into a devitalized mince, this procedure has no effect when applied to a viable mince.

Astronaut-induced disturbances in microgravity.

This Note describes the dynamic load sensors (DLS) spaceflight experiment that measured middeck astronaut-induced disturbances during the 14-day STS-62 Space Shuttle mission in March 1994. The DLS experiment was flown in conjunction with the reflight of the Middeck 0-Gravity Dynamics Experiment (MODE). The objective of MODE was to investigate effects of the microgravity environment on large space structures. Where Skylab experiments focused on measuring the forces exerted during vigorous soaring activities, the DLS experiment quantified the reaction forces and moments exerted by the crew going about their normal on-orbit activities. The objective of this Note is to present DLS force data and frequency analysis that characterize astronaut-induced loads during spaceflight.

Lack of myoblasts migration between transplanted and host muscles of mdx and normal mice.

Extensor digitorum longus muscles of normal mice (C57BL/10ScSn hereafter called C57) were orthotopically transplanted into dystrophin-deficient mice (mdx) and reciprocally, mdx Extensor digitorum longus muscles were transplanted into C57 mice. After an initial phase of degeneration, transplanted muscles regenerate nearly completely, as evaluated from the maximum isometric force of muscles isolated 60 days after the surgery. In other similar experiments, instead of isolating the grafted muscles, we excised the antero-external muscles of the leg, including the grafted muscle. Cryostat cross-sections at three levels along the muscles were immunostained with an anti-dystrophin antibody. No muscle cells of dystrophin-deficient muscles grafted into normal mice took the antibody except a few 'revertant' fibres, while all the muscle cells of the normal host were immunostained. Reciprocally, all the muscles cells of normal grafts were stained, whilst no antibody stained the cells of the surrounding muscles of the dystrophin-deficient host. These experiments show that very few if any of the myoblasts or muscle precursor cells, active during the regeneration of grafted muscle, migrate into the adjacent muscles. These results could be explained by the absence, in our work, of injuries of the grafted and adjacent host muscles epimysium and the absence of extensive inflammatory reactions. This lack of myoblast mobility suggest that when myoblast transfer is applied to muscle therapy, it will be necessary to inject myoblasts within each muscle to obtain an efficient treatment.

The origin of muscle stem cells in rat triceps surae regenerating after mincing.

Rat triceps surae was minced and orthotopically autografted. Twitch time to peak, maxima tetanic tension, lactate dehydrogenase activity and total creatine concentration were measured in muscles regenerating for 30, 60 and 90 days. If the minces were frozen and thawed before grafting, muscle regeneration was suppressed. If they were further heated before grafting, muscle regeneration was also suppressed. If one half of the mince was either frozen and thawed or frozen, thawed and heated, and then recombined with the remaining half, muscle regeneration was delayed. However, at 90 days, 'intensive properties' (twitch time to peak, maximum tetanic tension, total creatine concentration and lactate dehydrogenase activity) of regenerates obtained from such partially treated minces were similar to those of regenerates obtained from untreated minces although their 'extensive properties' (weight and maximal tetanic force) were approximately halved. The extent of regeneration depends on the mass of untreated mince autografted and thus, presumably, on the number of viable muscle stem cells initially present in the mince.

Subunit composition of native myosin isoenzymes of some striated mammalian muscles.

Six "native" isomyosins of characteristic electrophoretic mobility are present in various proportions according to the muscle type (fast, slow or mixed). SM2 and SM1 contain MHC1; IM contains MHC2A; FM1, FM2 and FM3 contain MHC2A and MHC2B. SM2, SM1 and IM contain MLC1s; SM1, IM, FM2 and FM3 contain MLC1f; FM2 and FM1 contain MLC3f. The six isomyosins appear to separate on the base of their myosin light chain content.

Muscle regeneration induced by cells autografted in adult rats.

Right triceps surae of 3-week-old Wistar rats were minced and devitalized with liquid nitrogen, a treatment which completely inhibits their ability to regenerate when they are orthotopically autografted. In a first series of experiments, cells were isolated from the left triceps surae, mixed with the devitalized right mince and autografted; in a second series, cells were moreover allowed to proliferate in vitro for a few weeks before being grafted. The regenerates were examined 60 days after surgery. In the first series, all the regenerates were contractile and developed a maximal isometric tetanic force of 18 +/- 6 mN (n = 5); they contained 152 +/- 80 muscle fibres located proximally, the number of which decreased along the proximo-distal axis, being 24 +/- 24 in the median part of the regenerate. The muscle fibres appeared histologically normal except for their shortness (less than 10 mm) and narrowness (mean luminal diameter: 30 microns). In the second series, 2 out of 5 regenerates were comparable with those of the first series except that their fibres were shorter; the 3 other regenerates were unexcitable. These experiments demonstrate that cells isolated from an adult striated muscle are able to regenerate striated muscle fibres in an adult animal and that these cells can retain this property if they are grown in culture.