611 research outputs found
Okaramine insecticidal alkaloids show similar activity on both exon 3c and exon 3b variants of glutamate-gated chloride channels of the larval silkworm, Bombyx mori
The okaramine indole alkaloids were recently shown to be more selective than ivermectin in activating the glutamate-gated chloride channels of the silkworm larvae of Bombyx mori (BmGluCls). Those studies were carried out using the exon 3b variant as a representative of BmGluCls. However, it remains unknown whether okaramines are similarly effective on other silkworm GluCl variants and whether they share the same binding site as ivermectin on GluCls. To begin to address these questions, we examined the potency of four okaramines on the exon 3c variant of BmGluCls by two-electrode voltage clamp voltage recordings of glutamate-induced chloride currents. The potency of okaramines in activating the exon 3c BmGluCl agreed well with findings on the exon 3b BmGluCl and insecticidal potency. Okaramine B (10ÎŒM) reduced the maximum binding (Bmax) but not the dissociation constant (KD) of [(3)H]ivermectin in studies on plasma membrane fractions of HEK293 cells expressing the exon 3c variant. These findings indicate that activation of GluCls is important in the insecticidal actions of okaramines
Studies of aerosol at a coastal site using two aerosol mass spectrometry instruments and identification of biogenic particle types
International audienceDuring August 2004 an Aerosol Time-of-Flight Mass Spectrometer (TSI ATOFMS Model 3800-100) and an Aerodyne Aerosol Mass Spectrometer (AMS) were deployed at Mace Head during the NAMBLEX campaign. Single particle data (size, positive and negative mass spectra) from the ATOFMS were imported into ART 2a, a neural network algorithm, which assigns individual particles to clusters on the basis of their mass spectral similarities. Results are very consistent with previous time consuming manual classifications (Dall'Osto et al., 2004). Three broad classes were found: sea-salt, dust and carbon-containing particles, with a number of sub-classes within each. The Aerodyne (AMS) instrument was also used during NAMBLEX, providing online, real time measurements of the mass of non-refractory components of aerosol particles as function of their size. The ATOFMS detected a type of particle not identified in our earlier analysis, with a strong signal at m/z 24, likely due to magnesium. This type of particle was detected during the same periods as pure unreacted sea salt particles and is thought to be biogenic, originating from the sea surface. AMS data are consistent with this interpretation, showing an additional organic peak in the corresponding size range at times when the Mg-rich particles are detected. The work shows the ATOFMS and AMS to be largely complementary, and to provide a powerful instrumental combination in studies of atmospheric chemistry
The fungal alkaloid Okaramine-B activates an L-glutamate-gated chloride channel from Ixodes scapularis, a tick vector of Lyme disease
A novel L-glutamate-gated anion channel (IscaGluCl1) has been cloned from the black-legged tick, Ixodes scapularis, which transmits multiple pathogens including the agents of Lyme disease and human granulocytic anaplasmosis. When mRNA encoding IscaGluCl1 was expressed in Xenopus laevis oocytes, we detected robust 50â400âŻnA currents in response to 100âŻÎŒM L-glutamate. Responses to L-glutamate were concentration-dependent (pEC50 3.64âŻÂ±âŻ0.11). Ibotenate was a partial agonist on IscaGluCl1. We detected no response to 100âŻÎŒM aspartate, quisqualate, kainate, AMPA or NMDA. Ivermectin at 1âŻÎŒM activated IscaGluCl1, whereas picrotoxinin (pIC50 6.20âŻÂ±âŻ0.04) and the phenylpyrazole fipronil (pIC50 6.90âŻÂ±âŻ0.04) showed concentration-dependent block of the L-glutamate response. The indole alkaloid okaramine B, isolated from fermentation products of Penicillium simplicissimum (strain AK40) grown on okara pulp, activated IscaGluCl1 in a concentration-dependent manner (pEC50 5.43âŻÂ±âŻ0.43) and may serve as a candidate lead compound for the development of new acaricides
An L319F mutation in transmembrane region 3 (TM3) selectively reduces sensitivity to okaramine B of the Bombyx mori L-glutamate-gated chloride channel
Okaramines produced by Penicillium simplicissimum AK-40 activate l-glutamate-gated chloride channels (GluCls) and thus paralyze insects. However, the okaramine binding site on insect GluCls is poorly understood. Sequence alignment shows that the equivalent of residue Leucine319 of the okaramine B sensitive Bombyx mori (B. mori) GluCl is a phenylalanine in the okaramine B insensitive B. mori Îł-aminobutyric acid-gated chloride channel of the same species. This residue is located in the third transmembrane (TM3) region, a location which in a nematode GluCl is close to the ivermectin binding site. The B. mori GluCl containing the L319F mutation retained its sensitivity to l-glutamate, but responses to ivermectin were reduced and those to okaramine B were completely blocked
Design and Test of a Forward Neutron Calorimeter for the ZEUS Experiment
A lead scintillator sandwich sampling calorimeter has been installed in the
HERA tunnel 105.6 m from the central ZEUS detector in the proton beam
direction. It is designed to measure the energy and scattering angle of
neutrons produced in charge exchange ep collisions. Before installation the
calorimeter was tested and calibrated in the H6 beam at CERN where 120 GeV
electrons, muons, pions and protons were made incident on the calorimeter. In
addition, the spectrum of fast neutrons from charge exchange proton-lucite
collisions was measured. The design and construction of the calorimeter is
described, and the results of the CERN test reported. Special attention is paid
to the measurement of shower position, shower width, and the separation of
electromagnetic showers from hadronic showers. The overall energy scale as
determined from the energy spectrum of charge exchange neutrons is compared to
that obtained from direct beam hadrons.Comment: 45 pages, 22 Encapsulated Postscript figures, submitted to Nuclear
Instruments and Method
Triaxial deformation in 10Be
The triaxial deformation in Be is investigated using a microscopic
model. The states of two valence neutrons are classified
based on the molecular-orbit (MO) model, and the -orbit is introduced
about the axis connecting the two -clusters for the description of the
rotational bands. There appear two rotational bands comprised mainly of and , respectively, at low excitation energy, where the two
valence neutrons occupy or orbits. The
triaxiality and the -mixing are discussed in connection to the molecular
structure, particularly, to the spin-orbit splitting. The extent of the
triaxial deformation is evaluated in terms of the electro-magnetic transition
matrix elements (Davydov-Filippov model, Q-invariant model), and density
distribution in the intrinsic frame. The obtained values turned out to be
.Comment: 15 pages, latex, 3 figure
A Fungal Metabolite Asperparaline A Strongly and Selectively Blocks Insect Nicotinic Acetylcholine Receptors: The First Report on the Mode of Action
Asperparalines produced by Aspergillus japonicus JV-23 induce
paralysis in silkworm (Bombyx mori) larvae, but the target
underlying insect toxicity remains unknown. In the present study, we have
investigated the actions of asperparaline A on ligand-gated ion channels
expressed in cultured larval brain neurons of the silkworm using patch-clamp
electrophysiology. Bath-application of asperparaline A (10 ”M) had no
effect on the membrane current, but when delivered for 1 min prior to
co-application with 10 ”M acetylcholine (ACh), it blocked completely the
ACh-induced current that was sensitive to mecamylamine, a nicotinic
acetylcholine receptor (nAChR)-selective antaogonist. In contrast, 10 ”M
asperparaline A was ineffective on the Îł-aminobutyric acid- and
L-glutamate-induced responses of the Bombyx larval neurons. The
fungal alkaloid showed no-use dependency in blocking the ACh-induced response
with distinct affinity for the peak and slowly-desensitizing current amplitudes
of the response to 10 ”M ACh in terms of IC50 values of 20.2
and 39.6 nM, respectively. Asperparaline A (100 nM) reduced the maximum neuron
response to ACh with a minimal shift in EC50, suggesting that the
alkaloid is non-competitive with ACh. In contrast to showing marked blocking
action on the insect nAChRs, it exhibited only a weak blocking action on chicken
α3ÎČ4, α4ÎČ2 and α7 nAChRs expressed in Xenopus
laevis oocytes, suggesting a high selectivity for insect over
certain vertebrate nAChRs
Structure of the mirror nuclei Be and B in a microscopic cluster model
The structure of the mirror nuclei Be and B is studied in a
microscopic and three-cluster model
using a fully antisymmetrized 9-nucleon wave function. The two-nucleon
interaction includes central and spin-orbit components and the Coulomb
potential. The ground state of Be is obtained accurately with the
stochastic variational method, while several particle-unbound states of both
Be and B are investigated with the complex scaling method.The
calculation for Be supports the recent identification for the existence of
two broad states around 6.5 MeV, and predicts the and
states at about 4.5 MeV and 8 MeV, respectively. The
similarity of the calculated spectra of Be and B enables one to
identify unknown spins and parities of the B states. Available data on
electromagnetic moments and elastic electron scatterings are reproduced very
well. The enhancement of the 1 transition of the first excited state in
Be is well accounted for. The calculated density of Be is found to
reproduce the reaction cross section on a Carbon target. The analysis of the
beta decay of Li to Be clearly shows that the wave function of Be
must contain a small component that cannot be described by the simple model. This small component can be well accounted for by extending a
configuration space to include the distortion of the -particle to
and partitions.Comment: 24 page
Important role of the spin-orbit interaction in forming the 1/2^+ orbital structure in Be isotopes
The structure of the second 0^+ state of ^{10}Be is investigated using a
microscopic model based on the molecular-orbit (MO) model.
The second 0^+ state, which has dominantly the (1/2^+)^2 configuration, is
shown to have a particularly enlarged structure. The kinetic
energy of the two valence neutrons occupying along the axis is
reduced remarkably due to the strong clustering and, simultaneously,
the spin-orbit interaction unexpectedly plays important role to make the energy
of this state much lower. The mixing of states with different spin structure is
shown to be important in negative-parity states. The experimentally observed
small-level spacing between 1^- and 2^- (~ 300 keV) is found to be an evidence
of this spin-mixing effect. ^{12}{Be} is also investigated using
model, in which four valence neutrons are considered to
occupy the (3/2^-)^2(1/2^+)^2 configuration. The energy surface of ^{12}Be is
shown to exhibit similar characteristics, that the remarkable
clustering and the contribution of the spin-orbit interaction make the binding
of the state with (3/2^-)^2(1/2^+)^2 configuration properly stronger in
comparison with the closed p-shell (3/2^-)^2(1/2^-)^2 configuration.Comment: 14 pages, 4 figure
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