bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of dayside magnetic separatrix signatures in HF and incoherent scatter radar data
Authors: Blanchard G. T. , Ellington C. L. , Baker K. B.
Published: December 2003

Both high‐frequency (HF) and incoherent scatter (IS) radar have previously been used to identify the open‐closed magnetic field separatrix and to measure the magnetospheric reconnection rate. The HF radar signature of open magnetic field on the dayside is a high spectral width in the backscatter Doppler spectrum. The IS radar signature of closed field lines is the presence of ionization indicating boundary plasma sheet precipitation. We investigate the consistency of these different signatures of the separatrix and show that the consistency depends on the local reconnection electric field. The two signatures yield a consistent identification of the separatrix at local times where the reconnection electric field is low. In the merging gap, however, where the reconnection electric field is high, the signature in the HF radar signature moves several degrees equatorward of the signature in the IS radar. These observations are backed up by DMSP precipitating particle observations, which indicate that the IS radar technique is properly identifying the poleward edge of the dayside BPS precipitation but also that the trapping boundary of magnetospheric ions and the electron edge occur at a latitude consistent with the HF radar signature of the separatrix. These observations are consistent with the theory that a portion of the dayside BPS is on open magnetic field lines. The latitudinal width of the dayside BPS on open field lines is given by ΔΛ = 0.14°Erec[mV/m]. We conclude that the HF radar signature is the more accurate identifier of the magnetic separatrix in the region of active reconnection.
Initial observations with the Global Ultraviolet Imager (GUVI) in the NASA TIMED satellite mission
Authors: Christensen A. B. , Paxton L. J. , Avery S. , Craven J. , Crowley G. , Humm D. C. , Kil H. , Meier R. R. , Meng C.‐I. , Morrison D. , Ogorzalek B. S. , Straus P. , Strickland D. J. , Swenson R. M. , Walterscheid R. L. , Wolven B. , Zhang Y.
Published: December 2003

The Global Ultraviolet Imager (GUVI) instrument carried aboard the NASA TIMED satellite measures the spectral radiance of the Earth's far ultraviolet airglow in the spectral region from 120 to 180 nm using a cross‐track scanning spectrometer design. Continuous operation of the instrument provides images of the Earth's disk and limb in five selectable spectral bands. Also, spectra at fixed scanning mirror position can be obtained. Initial results demonstrate the quantitative functionality of the instrument for studies of the Earth's dayglow, aurora, and ionosphere. Moreover, through forward modeling, the abundance of the major constituents of the thermosphere, O, N2, and O2 and thermospheric temperatures can be retrieved from observations of the limb radiance. Variations of the column O/N2 ratio can be deduced from sunlit disk observations. In regions of auroral precipitation not only can the aurora regions be geographically located and the auroral boundaries identified, but also the energy flux Q, the characteristic energy Eo, and a parameter fo that scales the abundance of neutral atomic oxygen can be derived. Radiance due to radiative recombination in the ionospheric F region is evident from both dayside and nightside observations of the Earth's limb and disk, respectively. Regions of depleted F‐region electron density are evident in the tropical Appleton anomaly regions, associated with so‐called ionospheric “bubbles.” Access to the GUVI data is provided through the GUVI website www.timed.jhuapl.edu\guvi.
Case studies of coupling between the E and F regions during unstable sporadic‐E conditions
Authors: Kelley Michael C. , Haldoupis Christos , Nicolls Michael J. , Makela Jonathan J. , Belehaki Anna , Shalimov Sergei , Wong Victor K.
Published: December 2003

Simultaneous F‐region airglow, E‐region coherent‐scatter radar, and ionosonde observations were made in Greece during the summer sporadic‐E season in 2002. In this paper we report on two case studies during which patchy sporadic‐E layers were accompanied by midlatitude spread F, coherent VHF radar echoes (including two‐stream echoes), and traveling ionospheric disturbances registered by the airglow instrument. We argue that these events give strong evidence that polarization electric fields are built up in the E region and are mapped upward to the F region, creating rising and falling regions in the bottomside plasma. The resulting structure creates conditions for midlatitude spread F, as detected by the ionosonde. This correlation between patchy sporadic E and midlatitude spread F is further supported in a companion paper. Upward coupling of this sort is particularly efficient in regions of F‐region plasma uplift and airglow depletion, since the F‐region Pedersen conductivity is low which reduces the electrical load on the E‐region generator.
Motion of the dusk flank boundary layer caused by solar wind pressure changes and the Kelvin‐Helmholtz instability: 10–11 January 1997
Authors: Fairfield D. H. , Farrugia C. J. , Mukai T. , Nagai T. , Fedorov A.
Published: December 2003

During an interval of steady northward IMF on 10–11 January 1997, Geotail and Interball spacecraft data at X = −5 to −15 RE on the dusk flank reveal magnetopause boundary layer motions caused by both solar wind pressure discontinuities and the Kelvin‐Helmholtz instability. Several large, sudden changes in solar wind density caused the magnetopause to move across both spacecraft. Relative timing of these crossings along with corresponding geosynchronous and ground magnetic field changes allow study of the propagation of pressure fronts in the magnetosheath and the associated wave propagation in the magnetosphere. The wave in the boundary layer propagates down the tail faster than the pressure front in the magnetosheath, producing boundary motion ahead of the magnetosheath front. This boundary layer wave can bulge out the magnetopause, causing a spacecraft in the magnetosheath to become immersed in the magnetosphere for as long as 2 or 3 min before the higher density magnetosheath plasma arrives and compresses the boundary. The tailward convecting magnetosheath pressure front moves more slowly near the magnetopause than it does further out in the magnetosheath, distorting the front and enhancing the likelihood that the boundary layer wave will outrun the magnetosheath front. Integrating the velocity perpendicular to the boundary shows that the boundary waves can have amplitudes of at least 1 or 2 Re. During periods of steady solar wind pressure, waves with periods of several minutes are observed in a boundary layer that are consistent with exitation of the Kelvin‐Helmholtz instability. Magnetograms from five ground magnetometer chains show both pulsations initiated by the pressure discontinuities and ongoing wave trains probably related to the KH instability.
Low‐latitude ionospheric disturbance electric field effects during the recovery phase of the 19–21 October 1998 magnetic storm
Authors: Fejer B. G. , Emmert J. T.
Published: December 2003

Low‐latitude ionospheric electric fields and currents are often strongly disturbed during periods of enhanced geomagnetic activity. These perturbations can last for several hours after geomagnetic quieting. We use incoherent scatter radar measurements from Jicamarca and Arecibo during 19–21 October 1998 to study, for the first time, the low‐latitude disturbance electric fields during the recovery phase of a large magnetic storm. On 19 October the Jicamarca data showed initially large and short‐lived (time scale of about 10–20 min) upward and westward drift perturbations in the early afternoon sector, due to the penetration of strong magnetospheric electric fields probably driven by an increase in the solar wind dynamic pressure. Following the decrease of auroral activity, very strong afternoon and nighttime zonal and vertical disturbance dynamo drifts were observed over Jicamarca but, surprisingly, only small and sporadic perturbation drifts were present over Arecibo. The latitudinal variation of the daytime zonal disturbance dynamo drifts during this day is in good agreement with that previously observed for thermospheric disturbance winds. The disturbance dynamo drifts also indicate significantly different local, storm time, and possibly latitudinal dependences for their vertical/perpendicular and zonal drift components, suggesting large variations in both the amplitude and direction of the disturbance dynamo electric field vector. In the next day, during moderately disturbed conditions, the daytime perturbation drifts were small, but following transient increases in geomagnetic activity, large upward/perpendicular drifts were observed near dusk over Jicamarca and Arecibo, where simultaneous westward perturbation drifts were also seen. These perturbations are consistent with the occurrence of strong prompt penetration electric fields reaching the magnetic equator. The measured prompt penetration drift patterns are generally in good agreement with predictions from global convection models. Later at night, under moderately disturbed conditions, relatively large zonal and meridional disturbance dynamo electric fields were observed by the two radars. Our results illustrate the large variability of the low‐latitude perturbation electric fields relative to their climatological values after large storms, probably due to the importance of additional disturbance processes. They also indicate that a much deeper understanding of solar‐wind/magnetospheric/ionospheric processes is required for accurate predictions of these electric fields.
Toggling of seismicity by the 1997 Kagoshima earthquake couplet: A demonstration of time‐dependent stress transfer
Authors: Toda Shinji , Stein Ross
Published: December 2003

Two M ∼ 6 well‐recorded strike‐slip earthquakes struck just 4 km and 48 days apart in Kagoshima prefecture, Japan, in 1997, providing an opportunity to study earthquake interaction. Aftershocks are abundant where the Coulomb stress is calculated to have been increased by the first event, and they abruptly stop where the stress is dropped by the second event. This ability of the main shocks to toggle seismicity on and off argues that static stress changes play a major role in exciting aftershocks, whereas the dynamic Coulomb stresses, which should only promote seismicity, appear to play a secondary role. If true, the net stress changes from a sequence of earthquakes might be expected to govern the subsequent seismicity distribution. However, adding the stress changes from the two Kagoshima events does not fully capture the ensuing seismicity, such as its rate change, temporal decay, or migration away from the ends of the ruptures. We therefore implement a stress transfer model that incorporates rate/state friction, in which seismicity is treated as a sequence of independent nucleation events that are dependent on the fault slip, slip rate, and elapsed time since the last event. The model reproduces the temporal response of seismicity to successive stress changes, including toggling, decay, and aftershock migration. Nevertheless, the match of observed to predicted seismicity is quite imperfect, due perhaps to inadequate knowledge of several model parameters. However, to demonstrate the potential of this approach, we build a probabilistic forecast of larger earthquakes on the expected rate of small aftershocks, taking advantage of the large statistical sample the small shocks afford. Not surprisingly, such probabilities are highly time‐ and location‐dependent: During the first decade after the main shocks, the seismicity rate and the chance of successive large shocks are about an order of magnitude higher than the background rate and are concentrated exclusively in the stress triggering zones.
OH column abundance over Table Mountain Facility, California: Intra‐annual variations and comparisons to model predictions for 1997–2001
Authors: Mills Franklin P. , Cageao Richard P. , Sander Stanley P. , Allen Mark , Yung Yuk L. , Remsberg Ellis E. , Russell James M. , Richter Ulf
Published: December 2003

Measurements of the OH column abundance over the Jet Propulsion Laboratory's Table Mountain Facility (TMF) have been made since July 1997 at 10°–80° solar zenith angle using a Fourier transform ultraviolet spectrometer. The measured OH column at any solar zenith angle is typically larger in the afternoon than in the morning. The variations observed in the OH column abundance appear to result from changes in atmospheric conditions on a daily or longer timescale. The larger observed variations are statistically significant. Sensitivity coefficients describing how the OH column abundance is expected to change in response to changes in the concentrations of H2O, O3, NO, CO, and CH4 have been calculated on the basis of an analytic model. On the basis of these sensitivity coefficients and Halogen Occultation Experiment observations of O3, the net sensitivity of the OH column abundance to variations in O3 should be close to zero. The observed OH column abundance over TMF increased by about 25% from July 1997 to December 2001. This interannual trend in OH column abundance is not consistent with calculations that incorporate observed trends in H2O and O3 and is at least a factor of 2 larger than the calculated difference between solar minimum and maximum. Comparisons between measured and calculated normalized OH column abundances suggest that the sensitivity of OH to variations in H2O may be a factor of 2 larger than predicted in present models and that there is some other major driver for the observed variability in the OH column abundance that was not included in the present analysis.
East Antarctic ice core sulfur isotope measurements over a complete glacial‐interglacial cycle
Authors: Alexander B. , Thiemens M. H. , Farquhar J. , Kaufman A. J. , Savarino J. , Delmas R. J.
Published: December 2003

Both sulfur and oxygen isotopes of sulfate preserved in ice cores from Greenland and Antarctica have provided information on the relative sources of sulfate in the ice and their chemical transformation pathways in the atmosphere over various time periods. The mass‐independent fractionation in the oxygen isotopes of sulfate from the Vostok ice core from east Antarctica suggests that gas‐phase oxidation by the hydroxyl radical (OH) was relatively greater than aqueous‐phase oxidation by O3 and H2O2 during the last glacial period than during the Eemian and preindustrial Holocene. The complete sulfur isotopic composition (δ33S, δ34S, δ36S) from the same Vostok ice core samples along with δ34S measurements from the Dome C, east Antarctic ice core from this study lend support to these conclusions and reveal significant isotopic fractionation of δ34S during chemical transformation and transport to east Antarctica. These findings reveal that conservation of sulfur isotopic signatures upon transport cannot be assumed for the East Antarctic plateau over the time periods considered.
Clouds and sulfate are anticorrelated: A new diagnostic for global sulfur models
Authors: Koch Dorothy , Park Jeffrey , Del Genio Anthony
Published: December 2003

We consider the correlation between clouds and sulfate in order to assess the relative importance of cloud aqueous‐phase production of sulfate, precipatation scavenging of sulfate, and inhibition of gas‐phase sulfate production beneath clouds. Statistical analysis of observed daily cloud cover and sulfate surface concentrations in Europe and North America indicates a significant negative correlation between clouds and sulfate. This implies that clouds remove sulfate via precipitation scavenging and/or inhibit sulfate gas‐phase production more than they enhance sulfate concentration through aqueous‐phase production. Persistent sulfate/cloud anticorrelations at long timescales (8–64 days) apparently result from large‐scale dynamical influences on clouds, which in turn impact sulfate. A statistical analysis of output from the general circulation model (GCM) of the Goddard Institute for Space Studies (GISS) shows weak coherence between sulfate and cloud cover. However, there is stronger anticorrelation between the model's sulfate generated by gas‐phase oxidation and cloud cover. Sulfate/cloud anticorrelation in the GCM strengthens if we extinguish gas‐phase sulfate production beneath clouds, as should happen since the oxidant OH is photochemically generated. However the only way to achieve strong anticorrelation between total sulfate and clouds is by correcting our treatment of aqueous‐phase sulfate production. Our model, like many other global tracer models, released dissolved species (including sulfate) from clouds after each cloud time step rather than making release contingent upon cloud evaporation. After correcting this in the GISS model, more sulfate is rained out, the sulfate burden produced via the aqueous phase decreases to half its former amount, and the total sulfate burden is 25% lower.
Long‐range transport of Saharan dust to northern Europe: The 11–16 October 2001 outbreak observed with EARLINET
Authors: Ansmann Albert , Bösenberg Jens , Chaikovsky Anatoli , Comerón Adolfo , Eckhardt Sabine , Eixmann Ronald , Freudenthaler Volker , Ginoux Paul , Komguem Leonce , Linné Holger , Márquez Miguel Ángel López , Matthias Volker , Mattis Ina , Mitev Valentin , Müller Detlef , Music Svetlana , Nickovic Slobodan , Pelon Jacques , Sauvage Laurent , Sobolewsky Piotr , Srivastava Manoj K. , Stohl Andreas , Torres Omar , Vaughan Geraint , Wandinger Ulla , Wiegner Matthias
Published: December 2003

The spread of mineral particles over southwestern, western, and central Europe resulting from a strong Saharan dust outbreak in October 2001 was observed at 10 stations of the European Aerosol Research Lidar Network (EARLINET). For the first time, an optically dense desert dust plume over Europe was characterized coherently with high vertical resolution on a continental scale. The main layer was located above the boundary layer (above 1‐km height above sea level (asl)) up to 3–5‐km height, and traces of dust particles reached heights of 7–8 km. The particle optical depth typically ranged from 0.1 to 0.5 above 1‐km height asl at the wavelength of 532 nm, and maximum values close to 0.8 were found over northern Germany. The lidar observations are in qualitative agreement with values of optical depth derived from Total Ozone Mapping Spectrometer (TOMS) data. Ten‐day backward trajectories clearly indicated the Sahara as the source region of the particles and revealed that the dust layer observed, e.g., over Belsk, Poland, crossed the EARLINET site Aberystwyth, UK, and southern Scandinavia 24–48 hours before. Lidar‐derived particle depolarization ratios, backscatter‐ and extinction‐related Ångström exponents, and extinction‐to‐backscatter ratios mainly ranged from 15 to 25%, −0.5 to 0.5, and 40–80 sr, respectively, within the lofted dust plumes. A few atmospheric model calculations are presented showing the dust concentration over Europe. The simulations were found to be consistent with the network observations.
Error analysis for a long‐range lightning monitoring network of ground‐based receivers in Europe
Authors: Chronis Themis G. , Anagnostou Emmanouil N.
Published: December 2003

An experimental long‐range lightning detection system consisting of a network (ZEUS) of six ground‐based radio receivers has been deployed in Europe and has been operated since June 2001. The receivers detect and measure the electromagnetic signal emitted by a lightning source in the Very Low Frequency band, between 5 and 15 kHz (sferics), which propagates over thousands of kilometers in the Earth‐ionosphere waveguide. In this study, lightning location retrievals from the ZEUS network are compared against more definitive sources in order to investigate issues on long‐range lightning retrieval accuracy and detection efficiency. The validation study is carried out over three regions: the U.S. East Coast/Northwestern Atlantic, the African continent, and within the network (Spain). Data originate from the U.S. National Lightning Detection Network, the Lighting Imaging Sensor aboard the Tropical Rainfall Measurement Mission Satellite, and the Spanish National Lightning Network. We investigate the nature of the errors involved in the lightning location retrieval, and propose a new approach for moderating some of these effects. Location errors are shown to vary between 40 and 400 km (mode at 220 km) for very long ranges (>5000 km). Within the network, the distance error does not exceed 40 km (mode at 20 km). Random simulation results are shown to be in good agreement with validation data. Error reduction of 12% (or 20 km at long‐range) can be achieved by accommodating for the varying propagation velocities in the sferics wave. The long‐range detection efficiency is shown to have a mode at approximately 20% and a relatively small spread with no obvious deviation from day to night.
Production of “potential” cloud condensation nuclei associated with atmospheric new‐particle formation in northern Finland
Authors: Lihavainen H. , Kerminen V.‐M. , Komppula M. , Hatakka J. , Aaltonen V. , Kulmala M. , Viisanen Y.
Published: December 2003

During a 33‐month measurement period at a high‐latitude background site in northern Finland, a total of 103 new particle formation events were observed. In 19 cases, movement of the air masses allowed the observation of particle formation and growth over a sufficiently long time to investigate the production of “potential” cloud condensation nuclei (CCN) resulting from new‐particle formation. All the CCN formation events took place in relatively clean air that had traversed the Northern Atlantic/Arctic Ocean prior to arrival at our measurement site. The number of formed new, “potential” CCN varied significantly between the different events and correlated weakly with the number of new‐particles formed during the same events. This is consistent with recent theoretical suggestions of some sort of decoupling between atmospheric new‐particle formation and growth. The vapours responsible for the “potential” CCN production could not be identified but were mostly something else than sulfuric acid resulting from the oxidation of SO2 in the gas phase. Although atmospheric new‐particle formation is likely to give only a minor contribution to the overall CCN budget at our measurement site, the situation may be different over areas where new‐particle formation events are more common. At the very least, our results demonstrate that because of atmospheric new‐particle formation, it may not be possible to find any universal relation between the aerosol mass and cloud droplet number concentration that is applicable to clean conditions.
Downward propagation from the stratosphere to the troposphere: A comparison of the two hemispheres
Authors: Graversen Rune G. , Christiansen Bo
Published: December 2003

The variability in the middle‐ and high‐latitude stratosphere and troposphere on annual and intraannual timescales is investigated with focus on the differences between the two hemispheres. Results obtained with the National Centers for Environmental Prediction reanalysis data are compared to a general circulation model simulation. Although downward propagation of zonal mean zonal wind anomalies from the stratosphere to the troposphere are found on intraannual timescales in both hemispheres the two hemispheres show several differences. First, the intraannual variability is around 30% weaker in the southern hemisphere (SH) than in the northern hemisphere (NH). Second, in the SH the downward propagation is concentrated to the spring season while it is found during the whole winter half‐year in the NH. Third, the coupling between the stratosphere and the troposphere is weaker and faster in the SH compared to the NH. Also, the annual cycle of the zonal mean zonal wind is quite different in the two hemispheres. In the SH the annual cycle is strong, shows a downward propagation with a timescale of two months, and includes higher annual harmonics of considerable strength. In the NH the annual cycle is weaker, shows no downward propagation, and is more sinusoidal. In both hemispheres the annual cycle and the intraannual variability are weaker in the model than in the reanalysis. The downward propagation in the model closely resembles that of the reanalysis both on intraannual timescales and in the annual cycle. In the SH the model underestimates the importance of the higher annual harmonics.
Slope streak formation and dust deposition rates on Mars
Authors: Aharonson Oded , Schorghofer Norbert , Gerstell Marguerite F.
Published: December 2003

The Mars Orbiter Camera (MOC) has imaged, sometimes repeatedly, mass movements known as slope streaks, which are abundant in the dust‐covered regions on Mars. They are among the few known examples of contemporary surface changes. A survey of 173 collocated image pairs indicates that these features are currently forming at a high rate of ∼7% per existing streak, per Martian year. Either there is a complete turnover within a few decades or the streak population is currently increasing rapidly. Large spatial, as well as possible temporal, variations in the formation rate are obtained from these data. Streaks do not appear to fade over time periods comparable to their inverse formation rate of ∼28 years, as seen by analysis of Viking Orbiter images containing streaks that are still visible in MOC images. Gradual or stochastic variations in dust deposition may be needed to explain observations of changes in the formation rate, and its current imbalance with the fading rate.
Prospecting for horizontal surface displacements in Antelope Valley, California, using satellite radar interferometry
Authors: Hoffmann Jörn , Zebker Howard A.
Published: December 2003

We compare interferometric synthetic aperture radar displacement maps for Antelope Valley, California, derived for two different satellite orbit geometries to test the common assumption that surface displacements above deforming aquifer systems are purely vertical. This assumption greatly simplifies models of aquifer system deformation related to changes in groundwater flow and storage, permitting the use of one‐dimensional codes for characterizing the compaction occurring in the flow model. The analysis is complicated by interferometric phase noise and atmospheric signal contributions. We use a variance‐weighted least squares approach to optimally use the information contained in several interferograms. Our analysis of the displacement maps does not identify significant displacement differences for the two acquisition geometries, implying that the motions are indeed nearly vertical. Uncertainties in the interferometric phase measurement and atmospheric delay signals preclude any conclusion regarding the existence of horizontal displacements smaller than ∼2 cm. The absence of spatial correlation between the observable differences and the known subsidence field indicates that horizontal displacements are indeed negligible for inelastic aquifer system compaction in Antelope Valley.
Assessing the reliability of regional depth‐duration‐frequency equations for gaged and ungaged sites
Authors: Brath Armando , Castellarin Attilio , Montanari Alberto
Published: December 2003

Design storms are usually estimated by analyzing observed rainfall extremes. When there are no measured data for the location of interest, the design storm may be estimated using regional depth‐duration‐frequency equations (RDDFEs). The annual series of precipitation maxima obtained for a dense network of rain gages located in northern central Italy are analyzed in order to (1) investigate the statistical properties of the rainfall extremes and compare them with the characteristics reported in published studies, (2) develop RDDFEs for the estimation of design storms for storm durations from 1 to 24 hours and recurrence intervals up to 100 years in any location of the study area, and (3) assess the reliability of RDDFEs for ungaged locations through a comprehensive jackknife cross validation.
NO/cyclic GMP pathway mediates the relaxation of feline lower oesophageal sphincter
Authors: Jun C. H. , Lee T. S. , Sohn U. D.
Published: December 2003

1 We examined the role of the NO/cyclic GMP (cyclic GMP) pathway in nitric oxide (NO)‐ and vasoactive intestinal peptide (VIP)‐induced relaxation of feline lower oesophageal sphincter (LES). Furthermore, it was studied whether methylene blue, LY83583 and ODQ, which are soluble guanylate cyclase (sGC) inhibitors, could inhibit NO‐induced relaxation.

2 The nitric oxide synthase (NOS) inhibitor, N‐nitro‐l‐arginine (l‐NNA) had no effect in sodium nitropruside (SNP)‐induced relaxation, but 3‐morpholinosydnonimine‐N‐ethylcarbamide (SIN‐1)‐induced relaxation was decreased by the pretreatment of l‐NNA, which showed that SIN‐1, not SNP, could activate NOS to cause relaxation. Methylene blue and LY83583 did not inhibit the relaxation by SNP and SIN‐1. However, the more specific sGC inhibitor ODQ blocked the relaxation induced by NO donors.

3 To identify the relationship of NOS, sGC and adenylate cyclase in VIP‐induced relaxation, tissue were pretreated with l‐NNA and ODQ and SQ22536. These inhibitors produced significant inhibition of this response to VIP. The adenylyl cyclase inhibitor SQ 22536 also inhibited relaxation by VIP.

4 In conclusion, our data showed that SNP‐ and SIN‐1‐induced relaxation was mediated by sGC. Of sGC inhibitors, methylene blue and LY83583 were not adequate for the examination of NO donor‐induced feline LES smooth muscle relaxation. VIP also caused relaxation by the pathway involving NO and cGMP and cAMP.
Opposite effects of endogenous nitric oxide and prostaglandin F2α in the rat mesenteric bed
Authors: Peredo H. A.
Published: December 2003

1 The relationship between the effects of endogenous nitric oxide (NO) and prostanoids on the noradrenaline (NA)‐induced contractions and the mechanisms involved were investigated in the rat perfused mesenteric bed, using NG‐nitro‐l‐arginine methyl ester (l‐NAME), a NO synthase inhibitor and sodium nitroprusside (SNP), a NO donor.

2 The constrictor responses to NA were reduced to 50% by the cyclooxygenase inhibitor 10 μm indomethacin as well as by 1 μm SNP. When indomethacin and SNP were perfused simultaneously the contractions were further reduced.

3 The NA‐induced contractions were increased by the addition of 400 μml‐NAME and the addition of either indomethacin or SNP abolished such increases. The simultaneous perfusion of both agents further reduced the contractions.

4 Removal of the endothelium increased NA‐induced contractions to a similar extent as l‐NAME and this increase was abolished by indomethacin as well as by SNP.

5 The perfusion of 10 μm NA augmented the release of prostaglandin (PG) F2α by the mesenteric bed without modifications in any other prostanoid. In the presence of l‐NAME, this effect was further increased. However, SNP abolished the NA‐induced stimulation of PGF2α release.

6 In de‐endothelialized preparations NA also stimulated PGF2α production as observed in intact preparations. This effect was more marked in the presence of l‐NAME; in contrast, SNP abolished the stimulation.

7 In conclusion, the present results suggest an opposite action between NO and PGF2α on the NA‐induced contractions in the rat mesenteric bed.
Activation of peroxisome proliferator-activated receptor δ induces fatty acid β-oxidation in skeletal muscle and attenuates metabolic syndrome
Authors: Tanaka Toshiya , Yamamoto Joji , Iwasaki Satoshi , Asaba Hiroshi , Hamura Hiroki , Ikeda Yukio , Watanabe Mitsuhiro , Magoori Kenta , Ioka Ryoichi X. , Tachibana Keisuke , Watanabe Yuichiro , Uchiyama Yasutoshi , Sumi Koichi , Iguchi Haruhisa , Ito Sadayoshi , Doi Takefumi , Hamakubo Takao , Naito Makoto , Auwerx Johan , Yanagisawa Masashi , Kodama Tatsuhiko , Sakai Juro
Published: December 2003

In this study, we defined the role of peroxisome proliferator-activated receptor β/δ (PPARδ) in metabolic homeostasis by using subtype selective agonists. Analysis of rat L6 myotubes treated with the PPARδ subtype-selective agonist, GW501516, by the Affymetrix oligonucleotide microarrays revealed that PPARδ controls fatty acid oxidation by regulating genes involved in fatty acid transport, β-oxidation, and mitochondrial respiration. Similar PPARδ-mediated gene activation was observed in the skeletal muscle of GW501516-treated mice. Accordingly, GW501516 treatment induced fatty acid β-oxidation in L6 myotubes as well as in mouse skeletal muscles. Administration of GW501516 to mice fed a high-fat diet ameliorated diet-induced obesity and insulin resistance, an effect accompanied by enhanced metabolic rate and fatty acid β-oxidation, proliferation of mitochondria, and a marked reduction of lipid droplets in skeletal muscles. Despite a modest body weight change relative to vehicle-treated mice, GW501516 treatment also markedly improved diabetes as revealed by the decrease in plasma glucose and blood insulin levels in genetically obese
ob
/
ob
mice. These data suggest that PPARδ is pivotal to control the program for fatty acid oxidation in the skeletal muscle, thereby ameliorating obesity and insulin resistance through its activation in obese animals.
High-affinity salicylic acid-binding protein 2 is required for plant innate immunity and has salicylic acid-stimulated lipase activity
Authors: Kumar Dhirendra , Klessig Daniel F.
Published: December 2003

Salicylic acid (SA) is a critical hormone for signaling innate immunity in plants. Here we present the purification and characterization of SA-binding protein 2 (SABP2), a tobacco protein that is present in low abundance and specifically binds SA with high affinity. Sequence analysis predicted that SABP2 is a lipase belonging to the α/β fold hydrolase super family. Confirming this prediction, recombinant SABP2 exhibited lipase activity against several synthetic substrates. Moreover, this lipase activity was stimulated by SA binding and may generate a lipid-derived signal. Silencing of
SABP2
expression suppressed local resistance to tobacco mosaic virus, induction of pathogenesis-related 1 (
PR-1
) gene expression by SA, and development of systemic acquired resistance. Together, these results suggest that SABP2 is an SA receptor that is required for the plant immune response. We further propose that SABP2 belongs to a large class of ligand-stimulated hydrolases involved in stress hormone-mediated signal transduction.
Antitumor efficacy of cytotoxic drugs and the monoclonal antibody 806 is enhanced by the EGF receptor inhibitor AG1478
Authors: Johns Terrance G. , Luwor Rodney B. , Murone Carmel , Walker Francesca , Weinstock Janet , Vitali Angela A. , Perera Rushika M. , Jungbluth Achim A. , Stockert Elisabeth , Old Lloyd J. , Nice Edouard C. , Burgess Antony W. , Scott Andrew M.
Published: December 2003

Blockade of epidermal growth factor receptor (EGFR) signaling with specific inhibitors of the EGFR tyrosine kinase retards cellular proliferation and arrests the growth of tumor xenografts. AG1478, an inhibitor of the EGFR tyrosine kinase, is used in laboratory studies; however, its therapeutic potential has not been elucidated. Therefore, we evaluated an aqueous form of AG1478 for its antitumor activity in mice bearing human xenografts expressing the WT EGFR or a naturally occurring ligand-independent truncation of the EGFR [delta2–7 (de2–7) EGFR or EGFRvIII]. Parenteral administration of soluble AG1478 blocked phosphorylation of the EGFR at the tumor site and inhibited the growth of A431 xenografts that overexpress the WT EGFR and glioma xenografts expressing the de2–7 EGFR. Strikingly, even subtherapeutic doses of AG1478 significantly enhanced the efficacy of cytotoxic drugs, with the combination of AG1478 and temozolomide displaying synergistic antitumor activity against human glioma xenografts. AG1478 was also examined in combination with mAb 806, an anti-EGFR antibody that was raised against the de2–7 EGFR but unexpectedly also binds a subset of the EGFR expressed in cells exhibiting amplification of the
EGFR
gene. The combination of AG1478 and mAb 806 displayed additive, and in some cases synergistic, antitumor activity against tumor xenografts overexpressing the EGFR. Here, we demonstrate that different classes of inhibitors to the EGFR can have synergistic antitumor activity
in vivo
. These results establish the antitumor efficacy of the EGFR inhibitor AG1478 and provide a rationale for its clinical evaluation in combination with both chemotherapy and other EGFR therapeutics.
Protein phosphatase 2C binds selectively to and dephosphorylates metabotropic glutamate receptor 3
Authors: Flajolet Marc , Rakhilin Sergey , Wang Hong , Starkova Natalia , Nuangchamnong Nina , Nairn Angus C. , Greengard Paul
Published: December 2003

Cell surface receptor membrane localization is strongly dependent on protein-protein interactions often involving regulation by phosphorylation/dephosphorylation of the intracellular domains of membrane proteins. The present study was carried out to identify metabotropic glutamate receptor (mGluR) 3 regulatory binding proteins. Using the yeast two-hybrid technique, we found that the 50-aa C-terminal cytoplasmic tail of mGluR3 interacts specifically with protein phosphatase 2Cα (PP2Cα). This interaction was confirmed by GST pull-down and coimmunoprecipitation assays. mGluR3 interacts with PP2Cα, β, γ, and δ isoforms; however, among the mGluR family only mGluR3 interacted with PP2C. The minimal interacting domain of mGluR3 comprised residues 836-855. Alignment between mGluR3 and mGluR2, a closely related group II receptor, indicated that this domain is not conserved between the two receptors. The mGluR3 cytoplasmic C-terminal tail contains one phosphorylation site for protein kinase A (Ser-845), but the phosphatase that dephosphorylates this site has not been previously identified. We find that PP2C, but not PP1, PP2A, or PP2B, dephosphorylates the mGluR3 cytoplasmic tail
in vitro
. The dephosphorylated form of the mGluR3 cytoplasmic tail, but not the equivalent region of mGluR2, inhibited PP2C assayed by using [
32
P]casein as a substrate. However, phosphorylation of the mGluR3 cytoplasmic tail at Ser-845 inhibits the interaction with PP2C. These results indicate distinct functions for mGluR2 and mGluR3 and suggest a dynamic regulation of mGluR3 by PP2C.
Activation of a LTR-retrotransposon by telomere erosion
Authors: Scholes Derek T. , Kenny Alison E. , Gamache Eric R. , Mou Zhongming , Curcio M. Joan
Published: December 2003

Retrotransposons can facilitate repair of broken chromosomes, and therefore an important question is whether the host can activate retrotransposons in response to chromosomal lesions. Here we show that Ty1 elements, which are LTR-retrotransposons in
Saccharomyces cerevisiae
, are mobilized when DNA lesions are created by the loss of telomere function. Inactivation of telomerase in yeast results in progressive shortening of telomeric DNA, eventually triggering a DNA-damage checkpoint that arrests cells in G
2
/M. A fraction of cells, termed survivors, recover from arrest by forming alternative telomere structures. When telomerase is inactivated, Ty1 retrotransposition increases substantially in parallel with telomere erosion and then partially declines when survivors emerge. Retrotransposition is stimulated at the level of Ty1 cDNA synthesis, causing cDNA levels to increase 20-fold or more before survivors form. This response is elicited through a signaling pathway that includes Rad24, Rad17, and Rad9, three components of the DNA-damage checkpoint. Our findings indicate that Ty1 retrotransposons are activated as part of the cellular response to telomere dysfunction.
A comprehensive analysis of hydrogen peroxide-induced gene expression in tobacco
Authors: Vandenabeele Steven , Van Der Kelen Katrien , Dat James , Gadjev Ilya , Boonefaes Tom , Morsa Stijn , Rottiers Pieter , Slooten Luit , Van Montagu Marc , Zabeau Marc , Inzé Dirk , Van Breusegem Frank
Published: December 2003

Hydrogen peroxide plays a central role in launching the defense response during stress in plants. To establish a molecular profile provoked by a sustained increase in hydrogen peroxide levels, catalase-deficient tobacco plants (CAT1AS) were exposed to high light (HL) intensities over a detailed time course. The expression kinetics of >14,000 genes were monitored by using transcript profiling technology based on cDNA-amplified fragment length polymorphism. Clustering and sequence analysis of 713 differentially expressed transcript fragments revealed a transcriptional response that mimicked that reported during both biotic and abiotic stresses, including the up-regulation of genes involved in the hypersensitive response, vesicular transport, posttranscriptional processes, biosynthesis of ethylene and jasmonic acid, proteolysis, mitochondrial metabolism, and cell death, and was accompanied by a very rapid up-regulation of several signal transduction components. Expression profiling corroborated by functional experiments showed that HL induced photoinhibition in CAT1AS plants and that a short-term HL exposure of CAT1AS plants triggered an increased tolerance against a subsequent severe oxidative stress.
Ultrafast folding of α
3
D: A
de novo
designed three-helix bundle protein
Authors: Zhu Yongjin , Alonso Darwin O. V. , Maki Kosuke , Huang Cheng-Yen , Lahr Steven J. , Daggett Valerie , Roder Heinrich , DeGrado William F. , Gai Feng
Published: December 2003

Here, we describe the folding/unfolding kinetics of α
3
D, a small designed three-helix bundle. Both IR temperature jump and ultrafast fluorescence mixing methods reveal a single-exponential process consistent with a minimal folding time of 3.2 ± 1.2 μs (at ≈50°C), indicating that a protein can fold on the 1- to 5-μs time scale. Furthermore, the single-exponential nature of the relaxation indicates that the prefactor for transition state (TS)-folding models is probably ≥1 (μs)
–1
for a protein of this size and topology. Molecular dynamics simulations and IR spectroscopy provide a molecular rationale for the rapid, single-exponential folding of this protein. α
3
D shows a significant bias toward local helical structure in the thermally denatured state. The molecular dynamics-simulated TS ensemble is highly heterogeneous and dynamic, allowing access to the TS via multiple pathways.
Network component analysis: Reconstruction of regulatory signals in biological systems
Authors: Liao James C. , Boscolo Riccardo , Yang Young-Lyeol , Tran Linh My , Sabatti Chiara , Roychowdhury Vwani P.
Published: December 2003

High-dimensional data sets generated by high-throughput technologies, such as DNA microarray, are often the outputs of complex networked systems driven by hidden regulatory signals. Traditional statistical methods for computing low-dimensional or hidden representations of these data sets, such as principal component analysis and independent component analysis, ignore the underlying network structures and provide decompositions based purely on
a priori
statistical constraints on the computed component signals. The resulting decomposition thus provides a phenomenological model for the observed data and does not necessarily contain physically or biologically meaningful signals. Here, we develop a method, called network component analysis, for uncovering hidden regulatory signals from outputs of networked systems, when only a partial knowledge of the underlying network topology is available. The
a priori
network structure information is first tested for compliance with a set of identifiability criteria. For networks that satisfy the criteria, the signals from the regulatory nodes and their strengths of influence on each output node can be faithfully reconstructed. This method is first validated experimentally by using the absorbance spectra of a network of various hemoglobin species. The method is then applied to microarray data generated from yeast
Saccharamyces cerevisiae
and the activities of various transcription factors during cell cycle are reconstructed by using recently discovered connectivity information for the underlying transcriptional regulatory networks.
Extensive gene gain associated with adaptive evolution of poxviruses
Authors: McLysaght Aoife , Baldi Pierre F. , Gaut Brandon S.
Published: December 2003

Previous studies of genome evolution usually have involved one or two genomes and have thus been limited in their ability to detect the direction and rate of evolutionary change. Here, we use complete genome data from 20 poxvirus genomes to build a robust phylogeny of the
Poxviridae
and to study patterns of genome evolution. We show that, although there has been little gene order evolution, there are substantial differences between poxviruses in terms of genome content. Furthermore, we show that the rate of gene acquisition is not constant over time and that it has increased in the orthopox lineage (which includes smallpox and vaccinia). We also tested for positive selection on 204 groups of genes and show that a disproportionately high proportion of genes in the orthopox clade are under positive selection. The association of an increased rate of gene gain and positive selection is indicative of adaptive genome evolution. Many of the genes involved in these processes are likely to be associated with host–parasite coevolution.
Ligand selectivity by seeking hydrophobicity in thyroid hormone receptor
Authors: Borngraeber Sabine , Budny Mary-Jane , Chiellini Grazia , Cunha-Lima Suzana T. , Togashi Marie , Webb Paul , Baxter John D. , Scanlan Thomas S. , Fletterick Robert J.
Published: December 2003

Selective therapeutics for nuclear receptors would revolutionize treatment for endocrine disease. Specific control of nuclear receptor activity is challenging because the internal cavities that bind hormones can be virtually identical. Only one highly selective hormone analog is known for the thyroid receptor, GC-24, an agonist for human thyroid hormone receptor β. The compound differs from natural hormone in benzyl, substituting for an iodine atom in the 3′ position. The benzyl is too large to fit into the enclosed pocket of the receptor. The crystal structure of human thyroid hormone receptor β at 2.8-Å resolution with GC-24 bound explains its agonist activity and unique isoform specificity. The benzyl of GC-24 is accommodated through shifts of 3–4 Å in two helices. These helices are required for binding hormone and positioning the critical helix 12 at the C terminus. Despite these changes, the complex associates with coactivator as tightly as human thyroid hormone receptor bound to thyroid hormone and is fully active. Our data suggest that increased specificity of ligand recognition derives from creating a new hydrophobic cluster with ligand and protein components.
Enhanced biocontrol activity of
Trichoderma
through inactivation of a mitogen-activated protein kinase
Authors: Mendoza-Mendoza Artemio , Pozo María J. , Grzegorski Darlene , Martínez Pedro , García Juan M. , Olmedo-Monfil Vianey , Cortés Carlos , Kenerley Charles , Herrera-Estrella Alfredo
Published: December 2003

The production of lytic enzymes in
Trichoderma
is considered determinant in its parasitic response against fungal species. A mitogen-activated protein kinase encoding gene,
tvk1
, from
Trichoderma virens
was cloned, and its role during the mycoparasitism, conidiation, and biocontrol was examined in
tvk1
null mutants. These mutants showed a clear increase in the level of the expression of mycoparasitism-related genes under simulated mycoparasitism and during direct confrontation with the plant pathogen
Rhizoctonia solani
. The null mutants displayed an increased protein secretion phenotype as measured by the production of lytic enzymes in culture supernatant compared to the wild type. Consistently, biocontrol assays demonstrated that the null mutants were considerably more effective in disease control than the wild-type strain or a chemical fungicide. In addition,
tvk1
gene disruptant strains sporulated abundantly in submerged cultures, a condition that is not conducive to sporulation in the wild type. These data suggest that Tvk1 acts as a negative modulator during host sensing and sporulation in
T. virens
.