1,747 research outputs found
Oxidative phosphorylation efficiency, proton conductance and reactive oxygen species production of liver mitochondria correlates with body mass in frogs
ody size is a central biological parameter affecting most biological processes (especially energetics) and mitochondria is a key organelle controlling metabolism and is also the cell's main source of chemical energy. However, the link between body size and mitochondrial function is still unclear, especially in ectotherms. In this study, we investigated several parameters of mitochondrial bioenergetics in the liver of three closely related species of frogs (the common frog Rana temporaria, the marsh frog Pelophylax ridibundus and the bull frog Lithobates catesbeiana). These particular species were chosen due to their differences in adult body mass. We found that the mitochondrial coupling efficiency was markedly increased with animal size, which lead to a higher ATP production (+70%) in the larger frogs (L. catesbeiana) compared to the smaller frogs (R. temporaria). This was essentially driven by a strong negative dependence of mitochondrial proton conductance on body mass. Liver mitochondria from the larger frogs (L. catesbeiana) displayed 50% of the proton conductance of mitochondria from the smaller frogs (R. temporaria). Contrary to our prediction, the low mitochondrial proton conductance measured in L. catesbeiana was not associated with higher radical oxygen species production. Instead, liver mitochondria from the larger individuals produced significantly lower radical oxygen species than those from the smaller frogs. Collectively, the data shows that key bioenergetics parameters of mitochondria (proton leak, ATP production efficiency and radical oxygen species production) are correlated with body mass in frogs. This research expands our understanding of the relationship between mitochondrial function and the evolution of allometric scaling in ectotherms
L'influence du climat familial sur l'investissement scolaire de collégiens de troisiÚme
RESUME En s'appuyant sur les rĂ©sultats d'Ă©tudes antĂ©rieures, nous mettons ici Ă l'Ă©preuve l'influence des modes de communication et de cohĂ©sion entre les membres de la famille sur l'investissement scolaire des collĂ©giens de 3Ăšme gĂ©nĂ©rale. Concernant son travail scolaire, le jeune peut ĂȘtre en attente de soutien et d'encouragement de la part de ses parents. Le manque d'implication parentale Ă l'Ă©cole contribue dĂšs lors Ă un rapport Ă l'Ă©cole plus problĂ©matique. Par ailleurs, des travaux rĂ©cents soulignent combien les relations harmonieuses entre parents et adolescents ainsi qu'une bonne communication favorisent chez l'adolescent un meilleur investissement scolaire. On constate Ă©galement que dans ces cas les adolescents vont rechercher le plus souvent des conseils auprĂšs des parents quant Ă leur devenir scolaire et professionnel. Inversement, il n'est pas rare de trouver chez ceux dont les relations et la communication sont moins harmonieuses, des signes de dĂ©mobilisation voire des attitudes de dĂ©crochage scolaire. Pour investiguer ces dimensions, nous avons soumit Ă 125 collĂ©giens, garçons et filles, deux questionnaires : l'un portant sur le Climat familial de Cloutier, Champoux et Jacques (1994) et l'autre, sur le vĂ©cu et l'investissement scolaire du jeune issu de l'enquĂȘte de PrĂȘteur, FĂ©chant et Constans (2003). Les principaux rĂ©sultats font ressortir quelques liaisons entre le climat familial et certains indicateurs du vĂ©cu et de l'investissement scolaire Ă l'adolescence. Les adolescents interrogĂ©s se sentent plutĂŽt bien en famille. Bien qu'ils soient 70% Ă accepter l'Ă©cole et son organisation, pour certains d'entre eux, ce sont surtout l'incomprĂ©hension de la part des professeurs, la difficultĂ© des apprentissages et l'organisation des cours (emploi du temps et de cours peu intĂ©ressants), qui ressortent comme Ă©lĂ©ments explicatifs d'un vĂ©cu scolaire peu enrichissant et d'un faible investissement Ă l'Ă©cole. Par ailleurs, le soutien parental apparaĂźt dĂ©terminant pour faciliter le rapport Ă l'Ă©cole Ă l'adolescence
31P Magnetic resonance spectroscopy study of phosphocreatine recovery kinetics in skeletal muscle: the issue of intersubject variability
AbstractWe have analyzed by 31P MRS the relationship between kinetic parameters of phosphocreatine (PCr) recovery and end-of-exercise status under conditions of moderate and large acidosis induced by dynamic exercise. Thirteen healthy subjects performed muscular contractions at 0.47 Hz (low frequency, moderate exercise) and 0.85 Hz (high frequency, heavy exercise). The rate constant of PCr resynthesis (kPCr) varied greatly among subjects (variation coefficients: 43 vs. 57% for LF vs. HF exercises) and protocols (kPCr values: 1.3±0.5 minâ1 vs. 0.9±0.5 minâ1 for LF vs. HF exercises, P<0.03). The large intersubject variability can be captured into a linear relationship between kPCr, the amount of PCr consumed ([PCr2]) and pH reached at the end of exercise (pHend) (kPCr=â3.3+0.7 pHend-0.03 [PCr2]; P=0.0007; r=0.61). This dual relationship illustrates that mitochondrial activity is affected by end-of-exercise metabolic status and allows reliable comparisons between control, diseased and trained muscles. In contrast to kPCr, the initial rate of PCr recovery and the maximum oxidative capacity were always constant whatever the metabolic conditions of end-of-exercise and can then be additionally used in the identification of dysfunctions in the oxidative metabolic pathway
Nuclear break-up of 11Be
The break-up of 11Be was studied at 41AMeV using a secondary beam of 11Be
from the GANIL facility on a 48Ti target by measuring correlations between the
10Be core, the emitted neutrons and gamma rays. The nuclear break-up leading to
the emission of a neutron at large angle in the laboratory frame is identified
with the towing mode through its characteristic n-fragment correlation. The
experimental spectra are compared with a model where the time dependent
Schrodinger equation (TDSE) is solved for the neutron initially in the 11 Be. A
good agreement is found between experiment and theory for the shapes of neutron
experimental energies and angular distributions. The spectroscopic factor of
the 2s orbital is tentatively extracted to be 0.46+-0.15. The neutron emission
from the 1p and 1d orbitals is also studied
Probing pre-formed alpha particles in the ground state of nuclei
In this Letter, we report on alpha particle emission through the nuclear
break-up in the reaction 40Ca on a 40Ca target at 50A MeV. It is observed that,
similarly to nucleons, alpha particles can be emitted to the continuum with
very specific angular distribution during the reaction. The alpha particle
properties can be understood as resulting from an alpha cluster in the daughter
nucleus that is perturbed by the short range nuclear attraction of the
collision partner and emitted. A time-dependent theory that describe the alpha
particle wave-function evolution is able to reproduce qualitatively the
observed angular distribution. This mechanism offers new possibilities to study
alpha particle properties in the nuclear medium.Comment: 4 pages, 3 figure
Overexpression of Mouse D-Type Cyclins Accelerates G(1) Phase in Rodent Fibroblasts
Mammalian D-type cyclins are growth factor-regulated, delayed early response genes that are presumed to control progression through the G1 phase of the cell cycle by governing the activity of cyclin-dependent kinases (cdks). Overexpression of mouse cyclin D1 in serum-stimulated mouse NIH-3T3 and rat-2 fibroblasts increased their rates of G0 to S- and G1- to S-phase transit by several hours, leading to an equivalent contraction of their mean cell generation times. Although such cells remained contact inhibited and anchorage dependent, they manifested a reduced serum requirement for growth and were smaller in size than their normal counterparts. Ectopic expression of cyclin D2 in rodent fibroblasts, either alone or together with exogenous cdk4, shortened their G0- to S-phase interval and reduced their serum dependency, but cyclin D2 alone did not alter cell size significantly. When cells were microinjected during the G2 interval with a monoclonal antibody specifically reactive to cyclin D1, parental rodent fibroblasts and derivatives overexpressing this cyclin were inhibited from entering S phase, but cells injected near the G1/S phase transition were refractory to antibody-induced growth suppression. Thus, cyclin D1, and most likely D2, are rate limiting for G1progression
The secondary eclipses of WASP-19b as seen by the ASTEP 400 telescope from Antarctica
The ASTEP (Antarctica Search for Transiting ExoPlanets) program was
originally aimed at probing the quality of the Dome C, Antarctica for the
discovery and characterization of exoplanets by photometry. In the first year
of operation of the 40 cm ASTEP 400 telescope (austral winter 2010), we
targeted the known transiting planet WASP-19b in order to try to detect its
secondary transits in the visible. This is made possible by the excellent
sub-millimagnitude precision of the binned data. The WASP-19 system was
observed during 24 nights in May 2010. The photometric variability level due to
starspots is about 1.8% (peak-to-peak), in line with the SuperWASP data from
2007 (1.4%) and larger than in 2008 (0.07%). We find a rotation period of
WASP-19 of 10.7 +/- 0.5 days, in agreement with the SuperWASP determination of
10.5 +/- 0.2 days. Theoretical models show that this can only be explained if
tidal dissipation in the star is weak, i.e. the tidal dissipation factor Q'star
> 3.10^7. Separately, we find evidence for a secondary eclipse of depth 390 +/-
190 ppm with a 2.0 sigma significance, a phase consistent with a circular orbit
and a 3% false positive probability. Given the wavelength range of the
observations (420 to 950 nm), the secondary transit depth translates into a day
side brightness temperature of 2690(-220/+150) K, in line with measurements in
the z' and K bands. The day side emission observed in the visible could be due
either to thermal emission of an extremely hot day side with very little
redistribution of heat to the night side, or to direct reflection of stellar
light with a maximum geometrical albedo Ag=0.27 +/- 0.13. We also report a
low-frequency oscillation well in phase at the planet orbital period, but with
a lower-limit amplitude that could not be attributed to the planet phase alone,
and possibly contaminated with residual lightcurve trends.Comment: Accepted for publication in Astronomy and Astrophysics, 13 pages, 13
figure
- âŠ