1,049 research outputs found
Implications of progesterone metabolism in MA-10 cells for accurate measurement of the rate of steroidogenesis
In virtually all studies with MA-10 cells, progesterone RIAs have been
used to measure steroid synthesis. To test whether progesterone is a
stable end product, we investigated the metabolism of added tritiated
progesterone and pregnenolone in MA-10 cells over a period of 3 h.
Steroids were then extracted, separated by HPLC, and identified by GC/MS.
We found that more than 70% of radiolabeled steroids were converted to at
least five different metabolites. A major metabolite (40%) was 5
alpha-pregnan-3 alpha or 3 beta-ol-20one. Similar studies, using
radiolabeled T, demonstrated conversion to dihydrotestosterone and two
forms of 5 alpha-androstane-diols. These data indicate the presence of
active 5 alpha-reductase and 3 alpha- and/or 3 beta-hydroxysteroid
dehydrogenase activities in MA-10 cells. Because these results suggest
that progesterone is an unstable end product, to gauge the level of active
metabolism, we incubated cells in the presence of inhibitors of
pregnenolone metabolism and assessed pregnenolone levels by RIA. We
discovered that basal levels of steroidogenesis in MA-10 cells were
considerably higher than previously estimated. Moreover, dibutyryl
cAMP-stimulated steroid production was linear over more than 13 h, in
contrast to previous findings that measured progesterone levels. Other
consequences of inaccurate assessment of steroidogenic activity in MA-10
cells because of the application of the progesterone assay are discussed
Specific dose-dependent effects of ethane 1,2-dimethanesulfonate in rat and mouse Leydig cells and non-steroidogenic cells on programmed cell death
The mechanism by which ethane 1,2-dimethanesulfonate (EDS) selectively
kills Leydig cells is poorly understood. To characterize further the
cell-specific actions of EDS, we studied biochemical and morphological
changes during apoptosis in different Leydig cell and non-steroidogenic
cell models.Rat testicular and H540 tumor Leydig cells were killed by 1-2
mM EDS, whereas 20 mM EDS were required for MA-10 cells. This higher
concentration of EDS was also necessary for activation of apoptosis in
non-steroidogenic Chinese hamster ovary cells, whereas COS-1 monkey kidney
cells were resistant. These variable effects of EDS on apoptosis were
independent of new protein synthesis and, interestingly, could be delayed
by co-incubation with dibutyrl cyclic AMP. Along with cell death, we also
observed chromosomal fragmentation and other hallmarks indicative of
apoptosis as evidenced by DNA laddering and fluorescent microscopy.
Time-lapse photography with a confocal microscope showed that the time of
onset, duration and even the sequence of apoptotic events between
individual H540 cells was heterogeneous. When the dose of EDS was
gradually increased from 2 to 10 mM, the proportion of cells showing
normal apoptotic features gradually decreased. Intriguingly, treatment
with 10 mM EDS did not result in death for most cells and was marked by an
absence of DNA laddering and ultrastructural features of apoptosis and
necrosis. However, incubation with 20 mM EDS resulted in necrosis.These
results demonstrated that the effects of EDS on cell survival are not
specific to Leydig cells, that different cell types have different
sensitivities to EDS and that stimulation of the cAMP pathway may mitigate
EDS action. The data obtained with H540 cells further revealed that EDS
can induce two types of programmed cell death
Suppression of static stripe formation by next-neighbor hopping
We show from real-space Hartree-Fock calculations within the extended Hubbard
model that next-nearest neighbor (t') hopping processes act to suppress the
formation of static charge stripes. This result is confirmed by investigating
the evolution of charge-inhomogeneous corral and stripe phases with increasing
t' of both signs. We propose that large t' values in YBCO prevent static stripe
formation, while anomalously small t' in LSCO provides an additional reason for
the appearance of static stripes only in these systems.Comment: 4 pages, 5 figure
Minimizing Lmax for the single machine scheduling problem with family set-ups
A procedure for the single machine-scheduling problem of minimizing the maximum lateness for jobs with sequence independent set-ups is presented. The procedure provides optimal/near-optimal solutions over a wide range of problems. It performs well compared with other heuristics, and it is effective in finding solutions for large problems
Exploitative Strategies: Consequences for Individual Behavior, Social Structure, and Design of Institutions
The influence of seat backrest angle on perceived discomfort during exposure to vertical whole-body vibration
National and International Standards (e.g. BS 6841 and ISO 2631-1) provide methodologies for the measurement and assessment of whole-body vibration in terms of comfort and health. The EU Physical Agents (Vibration) Directive (PAVD) provides criteria by which vibration magnitudes can be assessed. However, these standards only consider upright seated (90°) and recumbent (0°) backrest angles, and do not provide guidance for semi-recumbent postures. This article reports an experimental programme that investigated the effects of backrest angle on comfort during vertical whole-body vibration. The series of experiments showed that a relationship exists between seat backrest angle, whole-body vibration frequency and perceived levels of discomfort. The recumbent position (0°) was the most uncomfortable and the semi-recumbent positions of 67.5° and 45° were the least uncomfortable. A new set of frequency weighting curves are proposed which use the same topology as the existing BS and ISO standards. These curves could be applied to those exposed to whole-body vibration in semi-recumbent postures to augment the existing standardised methods.
Practitioner Summary: Current vibration standards provide guidance for assessing exposures for seated, standing and recumbent positions, but not for semi-recumbent postures. This article reports new experimental data systematically investigating the effect of backrest angle on discomfort experienced. It demonstrates that most discomfort is caused in a recumbent posture and that least was caused in a semi-recumbent posture
Relating the Lorentzian and exponential: Fermi's approximation,the Fourier transform and causality
The Fourier transform is often used to connect the Lorentzian energy
distribution for resonance scattering to the exponential time dependence for
decaying states. However, to apply the Fourier transform, one has to bend the
rules of standard quantum mechanics; the Lorentzian energy distribution must be
extended to the full real axis instead of being bounded from
below (``Fermi's approximation''). Then the Fourier transform
of the extended Lorentzian becomes the exponential, but only for times , a time asymmetry which is in conflict with the unitary group time evolution
of standard quantum mechanics. Extending the Fourier transform from
distributions to generalized vectors, we are led to Gamow kets, which possess a
Lorentzian energy distribution with and have exponential
time evolution for only. This leads to probability predictions
that do not violate causality.Comment: 23 pages, no figures, accepted by Phys. Rev.
Quantum computation with two-level trapped cold ions beyond Lamb-Dicke limit
We propose a simple scheme for implementing quantum logic gates with a string
of two-level trapped cold ions outside the Lamb-Dicke limit. Two internal
states of each ion are used as one computational qubit (CQ) and the collective
vibration of ions acts as the information bus, i.e., bus qubit (BQ). Using the
quantum dynamics for the laser-ion interaction as described by a generalized
Jaynes-Cummings model, we show that quantum entanglement between any one CQ and
the BQ can be coherently manipulated by applying classical laser beams. As a
result, universal quantum gates, i.e. the one-qubit rotation and two-qubit
controlled gates, can be implemented exactly. The required experimental
parameters for the implementation, including the Lamb-Dicke (LD) parameter and
the durations of the applied laser pulses, are derived. Neither the LD
approximation for the laser-ion interaction nor the auxiliary atomic level is
needed in the present scheme.Comment: 12 pages, no figures, to appear in Phys. Rev.
Nanoscale tunable reduction of graphene oxide for graphene electronics
International audienceGraphene is now recognized as the most likely carbon-based successor material for CMOS electronics. Recently, interest in graphene oxide (GO) has risen for producing large-scale flexible conductors and for its potential to open an electronic gap in graphene structures. We report on a means to tune the topographical and electrical properties of graphene-based materials with nanoscopic resolution by local thermal reduction of GO with a nano-size tip. The reduced GO nanostructures show an increase in conductivity up to four orders of magnitude as compared to pristine GO. No sign of tip wear or sample tearing was observed. Variably conductive nanoribbons with dimensions down to 12 nm have been produced in oxidized epitaxial graphene films in a single step that is clean, rapid and reliable
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