59,618 research outputs found
Hormone-stimulated modulation of endocytic trafficking in osteoclasts
Copyright @ 2012 Stenbeck, Lawrence and Albert. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc. This article has been made available through the Brunel Open Access Publishing Fund.A precise control of vesicular trafficking is crucial not only for osteoclastic bone resorption, but also for the crosstalk between osteoclasts and osteoblasts, which regulates bone homeostasis. In addition to the release of growth factors and modulators, such as glutamate, flux through the intracellular trafficking routes could also provide the osteoclast with a monitoring function of its resorption activity. To establish the signaling pathways regulating trafficking events in resorbing osteoclasts, we used the bone conserving hormone calcitonin, which has the unique property of inducing osteoclast quiescence. Calcitonin acts through the calcitonin receptor and activates multiple signaling pathways. By monitoring trafficking of a fluorescent low molecular weight probe in mature, bone resorbing osteoclasts we show for the first time that calcitonin blocks endocytosis from the ruffled border by phospholipase C (PLC) activation. Furthermore, we identify a requirement for polyunsaturated fatty acids in endocytic trafficking in osteoclasts. Inhibition of PLC prior to calcitonin treatment restores endocytosis to 75% of untreated rates. This effect is independent of protein kinase C activation and can be mimicked by an increase in intracellular calcium. We thus define an essential role for intracellular calcium levels in the maintenance of endocytosis in osteoclasts.Arthritis Research UK Grant (18197)
Covariant Quantum Fields on Noncommutative Spacetimes
A spinless covariant field on Minkowski spacetime \M^{d+1} obeys the
relation where
is an element of the Poincar\'e group \Pg and is its unitary representation on quantum vector states. It
expresses the fact that Poincar\'e transformations are being unitary
implemented. It has a classical analogy where field covariance shows that
Poincar\'e transformations are canonically implemented. Covariance is
self-reproducing: products of covariant fields are covariant. We recall these
properties and use them to formulate the notion of covariant quantum fields on
noncommutative spacetimes. In this way all our earlier results on dressing,
statistics, etc. for Moyal spacetimes are derived transparently. For the Voros
algebra, covariance and the *-operation are in conflict so that there are no
covariant Voros fields compatible with *, a result we found earlier. The notion
of Drinfel'd twist underlying much of the preceding discussion is extended to
discrete abelian and nonabelian groups such as the mapping class groups of
topological geons. For twists involving nonabelian groups the emergent
spacetimes are nonassociative.Comment: 20 page
Vlasov tokamak equilibria with shearad toroidal flow and anisotropic pressure
By choosing appropriate deformed Maxwellian ion and electron distribution
functions depending on the two particle constants of motion, i.e. the energy
and toroidal angular momentum, we reduce the Vlasov axisymmetric equilibrium
problem for quasineutral plasmas to a transcendental Grad-Shafranov-like
equation. This equation is then solved numerically under the Dirichlet boundary
condition for an analytically prescribed boundary possessing a lower X-point to
construct tokamak equilibria with toroidal sheared ion flow and anisotropic
pressure. Depending on the deformation of the distribution functions these
steady states can have toroidal current densities either peaked on the magnetic
axis or hollow. These two kinds of equilibria may be regarded as a bifurcation
in connection with symmetry properties of the distribution functions on the
magnetic axis.Comment: 9 pages, 9 figure
Dynamic model of spherical perturbations in the Friedman universe. III. Automodel solutions
A class of exact spherically symmetric perturbations of retarding automodel
solutions linearized around Friedman background of Einstein equations for an
ideal fluid with an arbitrary barotrope value is obtained and investigated.Comment: 12 pages, 4 figures, 8 reference
Nonlinear translational symmetric equilibria relevant to the L-H transition
Nonlinear z-independent solutions to a generalized Grad-Shafranov equation
(GSE) with up to quartic flux terms in the free functions and incompressible
plasma flow non parallel to the magnetic field are constructed
quasi-analytically. Through an ansatz the GSE is transformed to a set of three
ordinary differential equations and a constraint for three functions of the
coordinate x, in cartesian coordinates (x,y), which then are solved
numerically. Equilibrium configurations for certain values of the integration
constants are displayed. Examination of their characteristics in connection
with the impact of nonlinearity and sheared flow indicates that these
equilibria are consistent with the L-H transition phenomenology. For flows
parallel to the magnetic field one equilibrium corresponding to the H-state is
potentially stable in the sense that a sufficient condition for linear
stability is satisfied in an appreciable part of the plasma while another
solution corresponding to the L-state does not satisfy the condition. The
results indicate that the sheared flow in conjunction with the equilibrium
nonlinearity play a stabilizing role.Comment: 26 pages, 16 figure
Multi-waveband Emission Maps of Blazars
We are leading a comprehensive multi-waveband monitoring program of 34
gamma-ray bright blazars designed to locate the emission regions of blazars
from radio to gamma-ray frequencies. The "maps" are anchored by sequences of
images in both total and polarized intensity obtained with the VLBA at an
angular resolution of ~ 0.1 milliarcseconds. The time-variable linear
polarization at radio to optical wavelengths and radio to gamma-ray light
curves allow us to specify the locations of flares relative to bright
stationary features seen in the images and to infer the geometry of the
magnetic field in different regions of the jet. Our data reveal that some
flares occur simultaneously at different wavebands and others are only seen at
some of the frequencies. The flares are often triggered by a superluminal knot
passing through the stationary "core" on the VLBA images. Other flares occur
upstream or even parsecs downstream of the core.Comment: 5 pages, including 2 figures; to be published in Journal of
Astrophysics and Astronomy, as part of proceedings of the meeting
"Multiwavelength Variability of Blazars" held in Guangzhou, China, in
September 201
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