1,156 research outputs found
Differential regulation by phosphatidylinositol 4,5-bisphosphate of pituitary plasma-membrane and cytosolic phosphoinositide kinases
Inhibition of calcium-independent phospholipase A impairs agonist-induced calcium entry in keratinocytes
BACKGROUND: In many cells, depletion of intracellular calcium (Ca2+) reservoirs triggers Ca2+ entry through store-operated Ca2+ channels in the plasma membrane. However, the mechanisms of agonist-induced calcium entry (ACE) in keratinocytes are not fully understood. OBJECTIVES: This study was designed to determine if pharmacological inhibition of calcium-independent phospholipase A (iPLA(2)) impairs ACE in normal human epidermal keratinocytes. METHODS: Confocal laser scanning microscopy was used to monitor the dynamics of Ca2+ signalling in keratinocytes loaded with the calcium-sensitive dye Fluo-4. Cells were stimulated with extracellular nucleotides [adenosine triphosphate (ATP) or uridine triphosphate (UTP)] or with lysophosphatidic acid (LPA), a bioactive lipid that regulates keratinocyte proliferation and differentiation. RESULTS: Both ATP and UTP induced Ca2+ release in primary human keratinocytes. This was not followed by robust Ca2+ influx when the experiments were performed in low Ca2+ (70 micromol L(-1)) medium. Upon elevation of extracellular Ca2+ to 1.2 mmol L(-1), however, a biphasic response consisting of an initial Ca2+ peak followed by an elevated plateau was observed. The plateau phase was inhibited when cells were treated with bromoenol lactone, a specific pharmacological inhibitor of iPLA(2). These findings indicate that iPLA(2) activity is required for ACE in keratinocytes. LPA also evoked Ca2+ release in keratinocytes but failed to induce sustained Ca2+ entry even when extracellular Ca2+ was elevated to 1.2 mmol L(-1). CONCLUSION: Our results demonstrate for the first time an important role for iPLA(2) in regulating ACE in primary human keratinocytes
Asymmetric correlation matrices: an analysis of financial data
We analyze the spectral properties of correlation matrices between distinct
statistical systems. Such matrices are intrinsically non symmetric, and lend
themselves to extend the spectral analyses usually performed on standard
Pearson correlation matrices to the realm of complex eigenvalues. We employ
some recent random matrix theory results on the average eigenvalue density of
this type of matrices to distinguish between noise and non trivial correlation
structures, and we focus on financial data as a case study. Namely, we employ
daily prices of stocks belonging to the American and British stock exchanges,
and look for the emergence of correlations between two such markets in the
eigenvalue spectrum of their non symmetric correlation matrix. We find several
non trivial results, also when considering time-lagged correlations over short
lags, and we corroborate our findings by additionally studying the asymmetric
correlation matrix of the principal components of our datasets.Comment: Revised version; 11 pages, 13 figure
Searches for supersymmetric particles in collisions up to 208 GeV, and interpretation of the results within the MSSM
Searches for Supersymmetric Particles in Collisions up to 208 GeV and Interpretation of the Results within the MSSM
A conscious rethink : Why is brain tissue commonly preserved in the archaeological record? Commentary on: Petrone P, Pucci P, Niola M, et al. Heat-induced brain vitrification from the Vesuvius eruption in C.E. 79. N Engl J Med 2020;382:383-4. DOI: 10.1056/NEJMc1909867
Brain tissue is ubiquitous in the archaeological record. Multiple, independent studies report the finding of black, resinous or shiny brain tissue, and Petrone et al. [2020 “Heat-induced Brain Vitrification from the Vesuvius Eruption in C.E. 79.” N Engl J Med. 382: 383–384; doi:10.1056/NEJMc1909867] raise the intriguing prospect of a role for vitrification in the preservation of ancient biomolecules. However, Petrone et al. (2020) have not made their raw data available, and no detailed laboratory or analytical methodology is offered. Issues of contamination and misinterpretation hampered a decade of research in biomolecular archaeology, such that addressing these sources of bias and facilitating validation of specious findings has become both routine and of paramount importance in the discipline. We argue that the evidence they present does not support their conclusion of heat-induced vitrification of human brain tissue, and that future studies should share palaeoproteomic data in an open access repository to facilitate comparative analysis of the recovery of ancient proteins and patterns of their degradation
Determination of the b quark mass at the M_Z scale with the DELPHI detector at LEP
An experimental study of the normalized three-jet rate of b quark events with
respect to light quarks events (light= \ell \equiv u,d,s) has been performed
using the CAMBRIDGE and DURHAM jet algorithms. The data used were collected by
the DELPHI experiment at LEP on the Z peak from 1994 to 2000. The results are
found to agree with theoretical predictions treating mass corrections at
next-to-leading order. Measurements of the b quark mass have also been
performed for both the b pole mass: M_b and the b running mass: m_b(M_Z). Data
are found to be better described when using the running mass. The measurement
yields: m_b(M_Z) = 2.85 +/- 0.18 (stat) +/- 0.13 (exp) +/- 0.19 (had) +/- 0.12
(theo) GeV/c^2 for the CAMBRIDGE algorithm. This result is the most precise
measurement of the b mass derived from a high energy process. When compared to
other b mass determinations by experiments at lower energy scales, this value
agrees with the prediction of Quantum Chromodynamics for the energy evolution
of the running mass. The mass measurement is equivalent to a test of the
flavour independence of the strong coupling constant with an accuracy of 7
permil.Comment: 24 pages, 10 figures, Accepted by Eur. Phys. J.
Study of Leading Hadrons in Gluon and Quark Fragmentation
The study of quark jets in e+e- reactions at LEP has demonstrated that the
hadronisation process is reproduced well by the Lund string model. However, our
understanding of gluon fragmentation is less complete. In this study enriched
quark and gluon jet samples of different purities are selected in three-jet
events from hadronic decays of the Z collected by the DELPHI experiment in the
LEP runs during 1994 and 1995. The leading systems of the two kinds of jets are
defined by requiring a rapidity gap and their sum of charges is studied. An
excess of leading systems with total charge zero is found for gluon jets in all
cases, when compared to Monte Carlo Simulations with JETSET (with and without
Bose-Einstein correlations included) and ARIADNE. The corresponding leading
systems of quark jets do not exhibit such an excess. The influence of the gap
size and of the gluon purity on the effect is studied and a concentration of
the excess of neutral leading systems at low invariant masses (<~ 2 GeV/c^2) is
observed, indicating that gluon jets might have an additional hitherto
undetected fragmentation mode via a two-gluon system. This could be an
indication of a possible production of gluonic states as predicted by QCD.Comment: 19 pages, 6 figures, Accepted by Phys. Lett.
Phospholipase C-eta enzymes as putative protein kinase C and Ca2+ signalling components in neuronal and neuroendocrine tissues
Phosphoinositol-specific phospholipase C enzymes (PLCs) are central to inositol lipid signalling pathways, facilitating intracellular Ca2+ release and protein kinase C activation. A sixth class of phosphoinositol-specific PLC with a novel domain structure, PLC-eta (PLCeta) has recently been discovered in mammals. Recent research, reviewed here, shows that this class consists of two enzymes, PLCeta1 and PLCeta2. Both enzymes hydrolyze phosphatidylinositol 4,5-bisphosphate and are more sensitive to Ca2+ than other PLC isozymes and are likely to mediate G-protein-coupled receptor (GPCR) signalling pathways. Both enzymes are expressed in neuron-enriched regions, being abundant in the brain. We demonstrate that they are also expressed in neuroendocrine cell lines. PLCeta enzymes therefore represent novel proteins influencing intracellular Ca2+ dynamics and protein kinase C activation in the brain and neuroendocrine systems as putative mediation of GPCR regulation
- …