714 research outputs found
Paclitaxel inhibits the activity and membrane localization of PKCα and PKCβI/II to elicit a decrease in stimulated calcitonin gene-related peptide release from cultured sensory neurons
Peripheral neuropathy is a dose-limiting and debilitating side effect of the chemotherapeutic drug, paclitaxel. Consequently, elucidating the mechanisms by which this drug alters sensory neuronal function is essential for the development of successful therapeutics for peripheral neuropathy. We previously demonstrated that chronic treatment with paclitaxel (3–5 days) reduces neuropeptide release stimulated by agonists of TRPV1. Because the activity of TRPV1 channels is modulated by conventional and novel PKC isozymes (c/nPKC), we investigated whether c/nPKC mediate the loss of neuropeptide release following chronic treatment with paclitaxel (300 nM; 3 and 5 days). Release of the neuropeptide, calcitonin gene-related peptide (CGRP), was measured as an index of neuronal sensitivity. Following paclitaxel treatment, cultured dorsal root ganglia sensory neurons were stimulated with a c/nPKC activator, phorbol 12,13-dibutyrate (PDBu), or a TRPV1 agonist, capsaicin, in the absence and presence of selective inhibitors of conventional PKCα and PKCβI/II isozymes (cPKC). Paclitaxel (300 nM; 3 days and 5 days) attenuated both PDBu- and capsaicin-stimulated release in a cPKC-dependent manner. Under basal conditions, there were no changes in the protein expression, phosphorylation or membrane localization of PKC α, βI or βII, however, paclitaxel decreased cPKC activity as indicated by a reduction in the phosphorylation of cPKC substrates. Under stimulatory conditions, paclitaxel attenuated the membrane translocation of phosphorylated PKC α, βI and βII, providing a rationale for the attenuation in PDBu- and capsaicin-stimulated release. Our findings suggest that a decrease in cPKC activity and membrane localization are responsible for the reduction in stimulated peptide release following chronic treatment with paclitaxel in sensory neurons
Electron Self-Energy of High Temperature Superconductors as Revealed by Angle Resolved Photoemission
In this paper, we review some of the work our group has done in the past few
years to obtain the electron self-energy of high temperature superconductors by
analysis of angle-resolved photoemission data. We focus on three examples which
have revealed: (1) a d-wave superconducting gap, (2) a collective mode in the
superconducting state, and (3) pairing correlations in the pseudogap phase. In
each case, although a novel result is obtained which captures the essense of
the data, the conventional physics used leads to an incomplete picture. This
indicates that new physics needs to be developed to obtain a proper
understanding of these materials.Comment: 5 pages, revtex, 3 encapsulated postscript figures, SNS97 proceeding
Ginzburg-Landau Expansion and the Slope of the Upper Critical Field in Disordered Superconductors with Anisotropic Pairing
It is demonstrated that the slope of the upper critical field
in superconductors with -wave pairing drops rather
fast with concentration of normal impurities, while in superconductors with
anisotropic -wave pairing grows, and in the limit of
strong disorder is described by the known dependences of the theory of
``dirty'' superconductors. This allows to use the measurements of in
disordered superconductors to discriminate between these different types of
pairing in high-temperature and heavy-fermion superconductors.Comment: 7 pages, 5 figures, RevTeX 3.0, 4 Postscript figures attached;
Submitted to JETP Letter
On the possibility of superconductivity in PrBa2Cu3O7
Recent reports about observations of superconductivity in PrBa2Cu3O7 raise a
number of questions: (i) of various theories striving to explain the Tc
suppression in PrxY{1-x}Ba2Cu3O7, are there any compatible with possible
superconductivity in stoichiometric PrBa2Cu3O7? (ii) if this superconductivity
is not an experimental artifact, are the superconducting carriers (holes) of
the same character as in the other high-Tc cuprates, or do they represent
another electronic subsystem? (iii) is the underlying mechanism the same as in
other high-Tc superconductors? I present an answer to the first two questions,
while leaving the last one open.Comment: 4 pages 4 eps fig
Effect of non-magnetic impurities on the gap of a superconductor as seen by angle-resolved photoemission
An analysis of angle-resolved photoemission (ARPES) experiments in the
superconducting state of the high \tc copper-oxides is presented. It is based
on a phenomenological weak-coupling BCS model which incorporates the
experimental normal state dispersion extracted from ARPES, and non-magnetic
impurity scattering in the presence of a order parameter (OP). It
is shown, that already in the pure case, the broadening by finite momentum
resolution of the analyzer leads to a finite region of apparent `gaplessness'
around the true node of the OP. Non-magnetic impurities further amplify this
effect by introducing additional spectral weight around zero frequency. At
sufficiently large impurity concentrations , this results
in an extended region of `gaplessness' up to ( the
angle on the Fermi surface) around the true node for a large range of moderate
to strong impurity potential strengths. Different ways to identify the presence
of impurity scattering in the ARPES spectra are proposed.Comment: 8 pages uuencoded gzipped Postscrip
Superconductivity in Pr2Ba4Cu7O15-delta with metallic double chains
We report superconductivity with =10K in
PrBaCuO compound possessing metallic double
chains. A reduction treatment on as-sintered samples causes not only the
enhanced metallic conduction but also the appearance of superconductivity
accompanied by the c-axis elongation due to oxygen deficiency
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