Strong Depolarization Research Articles

Linear Polarization, Circular Polarization, and Depolarization of Gamma-ray Bursts: A Simple Case of Jitter Radiation

Abstract Linear and circular polarizations of gamma-ray bursts (GRBs) have been detected recently. We adopt a simplified model to investigate GRB polarization characteristics in this paper. A compressed two-dimensional turbulent slab containing stochastic magnetic fields is considered, and jitter radiation can produce the linear polarization under this special magnetic field topology. Turbulent Faraday rotation measure (RM) of this slab makes strong wavelength-dependent depolarization. The jitter photons can also scatter with those magnetic clumps inside the turbulent slab, and a nonzero variance of the Stokes parameter V can be generated. Furthermore, the linearly and circularly polarized photons in the optical and radio bands may suffer heavy absorptions from the slab. Thus we consider the polarized jitter radiation transfer processes. Finally, we compare our model results with the optical detections of GRB 091018, GRB 121024A, and GRB 131030A. We suggest simultaneous observations of GRB multi-wavelength polarization in the future.

Virtual electrodes around anatomical structures and their roles in defibrillation.

BackgroundVirtual electrodes from structural/conductivity heterogeneities are known to elicit wavefront propagation, upon field-stimulation, and are thought to be important for defibrillation. In this work we investigate how the constitutive and geometrical parameters associated with such anatomical heterogeneities, represented by endo/epicardial surfaces and intramural surfaces in the form of blood-vessels, affect the virtual electrode patterns produced.Methods and resultsThe steady-state bidomain model is used to obtain, using analytical and numerical methods, the virtual electrode patterns created around idealized endocardial trabeculations and blood-vessels. The virtual electrode pattern around blood-vessels is shown to be composed of two dominant effects; current traversing the vessel surface and conductivity heterogeneity from the fibre-architecture. The relative magnitudes of these two effects explain the swapping of the virtual electrode polarity observed, as a function of the vessel radius, and aid in the understanding of the virtual electrode patterns predicted by numerical bidomain modelling. The relatively high conductivity of blood, compared to myocardium, is shown to cause stronger depolarizations in the endocardial trabeculae grooves than the protrusions.ConclusionsThe results provide additional quantitative understanding of the virtual electrodes produced by small-scale ventricular anatomy, and highlight the importance of faithfully representing the physiology and the physics in the context of computational modelling of field stimulation.

Optogenetic activation of VGLUT2-expressing excitatory neurons blocks epileptic seizure-like activity in the mouse entorhinal cortex

We investigated whether an anti-epileptic effect is obtained by selectively activating excitatory neurons expressing ChR2 under the promoter for the synaptic vesicular glutamate transporter 2 (VGLUT2). VGLUT2-expressing cells were optically stimulated while local field potential and whole-cell patch-clamp recordings were performed in mouse entorhinal cortical slices perfused with the proconvulsive compound 4-aminopyridine (4-AP). In control conditions, blue light flashes directly depolarized the majority of putative glutamatergic cells, which in turn synaptically excited GABAergic interneurons. During bath perfusion with 4-AP, photostimuli triggered a fast EPSP-IPSP sequence which was often followed by tonic-clonic seizure-like activity closely resembling spontaneous ictal discharges. The GABAA-receptor antagonist gabazine blocked the progression of both light-induced and spontaneous seizures. Surprisingly, prolonged photostimuli delivered during ongoing seizures caused a robust interruption of synchronous discharges. Such break was correlated with a membrane potential depolarization block in principal cells, while putative GABAergic interneurons changed their firing activity from a burst-like to an irregular single-spike pattern. These data suggest that photostimulation of glutamatergic neurons triggers seizure-like activity only in the presence of an intact GABAergic transmission and that selectively activating the same glutamatergic cells robustly interrupts ongoing seizures by inducing a strong depolarization block, resulting in the disruption of paroxysmal burst-like firing.

Interacting large-scale magnetic fields and ionized gas in the W50/SS433 system

The W50/SS433 system is an unusual Galactic outflow-driven object of debatable origin. We have used the Australia Telescope Compact Array (ATCA) to observe a new 198 pointing mosaic, covering $3^\circ \times 2^\circ$, and present the highest-sensitivity full-Stokes data of W50 to date using wide-field, wide-band imaging over a 2 GHz bandwidth centred at 2.1 GHz. We also present a complementary H$\alpha$ mosaic created using the Isaac Newton Telescope Photometric H$\alpha$ Survey of the Northern Galactic Plane (IPHAS). The magnetic structure of W50 is found to be consistent with the prevailing hypothesis that the nebula is a reanimated shell-like supernova remnant (SNR), that has been re-energised by the jets from SS433. We observe strong depolarization effects that correlate with diffuse H$\alpha$ emission, likely due to spatially-varying Faraday rotation measure (RM) fluctuations of $\ge48$ to 61 rad m$^{-2}$ on scales $\le4.5$ to 6 pc. We also report the discovery of numerous, faint, H$\alpha$ filaments that are unambiguously associated with the central region of W50. These thin filaments are suggestive of a SNR's shock emission, and almost all have a radio counterpart. Furthermore, an RM-gradient is detected across the central region of W50, which we interpret as a loop magnetic field with a symmetry axis offset by $\approx90^{\circ}$ to the east-west jet-alignment axis, and implying that the evolutionary processes of both the jets and the SNR must be coupled. A separate RM-gradient is associated with the termination shock in the Eastern ear, which we interpret as a ring-like field located where the shock of the jet interacts with the circumstellar medium. Future optical observations will be able to use the new H$\alpha$ filaments to probe the kinematics of the shell of W50, potentially allowing for a definitive experiment on W50's formation history.

Searching for a Potential Voltage Sensor Intrinsic to Pannexin Channels

Pannexins are a family of large, oligomeric ion channels involved in a number of broad physiological processes. As ATP release channels, pannexins have important implications for purinergic signaling pathways, especially in context of neurological signaling where ATP acts as a neurotransmitter, or in context of vascular signaling, where ATP regulates vasoconstriction. Pannexin-1 is the best characterized member of the pannexin family largely because it presents readily observable currents when expressed heterologously and studied using patch clamp electrophysiology. Curiously, pannexin-1 channels can be activated using strong depolarizing voltage potentials (greater than +20 mV), suggesting the presence of a voltage sensing motif not found in other members of the pannexin family. To localize a potential voltage sensor in pannexin-1, we borrowed domains from pannexin-3 - a member of the pannexin family not activated by a voltage stimulus - and generated chimeric channels. Interestingly, we find that the extracellular and intracellular domains of pannexin-1 are dispensable for voltage sensing, suggesting an intrinsic voltage sensor within the transmembrane domains of pannexin-1.

Increased Neuronal Depolarization Evoked by Autoantibodies in Diabetic Obstructive Sleep Apnea: Role for Inflammatory Protease(s) in Generation of Neurotoxic Immunoglobulin Fragment.

Obstructive sleep apnea increases in diabetes and morbid obesity. We tested a hypothesis that circulating autoantibodies in adult type 2 diabetes which increase in association with morbid obesity are capable of causing long-lasting neuronal depolarization and altered calcium release in mouse atrial cardiomyocytes. Protein-A eluates from plasma of 14 diabetic obstructive sleep apnea patients and 17 age-matched diabetic patients without sleep apnea were tested for effects on depolarization and neurite out growth in N2a mouse neuroblastoma cells. The mechanism of autoantibody-mediated neurite outgrowth inhibition was investigated in co-incubation experiments of diabetic obstructive sleep apnea autoantibodies with specific antagonists of G-protein coupled receptors or the RhoA/Rho kinase signaling pathway. Following long-term storage of the protein-A eluates (to allow spontaneous proteolysis and IgG subunit dissociation), plasma autoantibodies from diabetic obstructive sleep apnea, cancer or control patients were compared for enhancement of inhibitory effects on endothelial cell survival. Size exclusion chromatography performed (in the presence or absence of a specific membrane type 1-matrix metalloproteinase inhibitor) was used to characterize the IgG autoantibody subunit(s) or fragments associated with peak neurotoxicity in diabetic obstructive sleep apnea. Diabetic obstructive sleep apnea (n = 14) autoantibodies caused a significant increase (P = 0.01) in membrane depolarization in N2a mouse neuroblastoma cells compared to control diabetic patients (n = 15) not suffering with obstructive sleep apnea. Process extension in N2A mouse neuroblastoma cells was significantly inhibited (P = 0.01) by diabetic obstructive sleep apnea (n = 9) autoantibodies compared to effects from identical 10 μg/mL concentrations of control diabetic autoantibodies in patients without obstructive sleep apnea. Ten micromolar concentrations of SCH-202676, a G-protein coupled receptor antagonist (n = 5) or ten micromolar concentration of Y27632, a selective Rho kinase inhibitor (n = 6), each significantly prevented (P < 0.001) neurite outgrowth inhibition by diabetic obstructive sleep apnea autoantibodies. Autoantibodies in representative patients with obstructive sleep apnea and either atrial fibrillation or left ventricular hypertrophy evoked acute large increases in intracellular Ca2+ in HL-1 mouse atrial cardiomyocytes. The magnitude of intracellular Ca2+ release was dose-dependently significantly correlated to the electrocardiographic Cornell voltage-duration product. Gel filtration of diabetic obstructive sleep apnea autoantibodies revealed peak neurotoxicity associated with MWs corresponding to IgG light chain dimer(s), monomers or half-light chains as well as a novel ∼ 5.5 kD putative light chain fragment. These results suggest that diabetic obstructive sleep apnea autoantibodies may induce strong depolarization in neuronal cells and alter Ca2+ signaling in atrial cardiomyocytes consistent with a role in pathophysiology in subsets of diabetic obstructive sleep apnea having co-morbid atrial fibrillation or another clinically significant cardiac rhythm disturbance.

The multifaceted role of inhibitory interneurons in the dorsal lateral geniculate nucleus.

Intrinsic interneurons within the dorsal lateral geniculate nucleus (dLGN) provide a feed-forward inhibitory pathway for afferent visual information originating from the retina. These interneurons are unique because in addition to traditional axodendritic output onto thalamocortical neurons, these interneurons have presynaptic dendrites that form dendrodendritic synapses onto thalamocortical neurons as well. These presynaptic dendrites, termed F2 terminals, are tightly coupled to the retinogeniculate afferents that synapse onto thalamocortical relay neurons. Retinogeniculate stimulation of F2 terminals can occur through the activation of ionotropic and/or metabotropic glutamate receptors. The stimulation of ionotropic glutamate receptors can occur with single stimuli and produces a short-lasting inhibition of the thalamocortical neuron. By contrast, activation of metabotropic glutamate receptors requires tetanic activation and results in longer-lasting inhibition in the thalamocortical neuron. The F2 terminals are predominantly localized to the distal dendrites of interneurons, and the excitation and output of F2 terminals can occur independent of somatic activity within the interneuron thereby allowing these F2 terminals to serve as independent processors, giving rise to focal inhibition. By contrast, strong transient depolarizations at the soma can initiate a backpropagating calcium-mediated potential that invades the dendritic arbor activating F2 terminals and leading to a global form of inhibition. These distinct types of output, focal versus global, could play an important role in the temporal and spatial roles of inhibition that in turn impacts thalamocortical information processing.

The Hv1 proton channel responds to mechanical stimuli.

The voltage-gated proton channel, Hv1, is expressed in tissues throughout the body and plays important roles in pH homeostasis and regulation of NADPH oxidase. Hv1 operates in membrane compartments that experience strong mechanical forces under physiological or pathological conditions. In microglia, for example, Hv1 activity is potentiated by cell swelling and causes an increase in brain damage after stroke. The channel complex consists of two proton-permeable voltage-sensing domains (VSDs) linked by a cytoplasmic coiled-coil domain. Here, we report that these VSDs directly respond to mechanical stimuli. We find that membrane stretch facilitates Hv1 channel opening by increasing the rate of activation and shifting the steady-state activation curve to less depolarized potentials. In the presence of a transmembrane pH gradient, membrane stretch alone opens the channel without the need for strong depolarizations. The effect of membrane stretch persists for several minutes after the mechanical stimulus is turned off, suggesting that the channel switches to a "facilitated" mode in which opening occurs more readily and then slowly reverts to the normal mode observed in the absence of membrane stretch. Conductance simulations with a six-state model recapitulate all the features of the channel's response to mechanical stimulation. Hv1 mechanosensitivity thus provides a mechanistic link between channel activation in microglia and brain damage after stroke.

Polarization transfer in Rayleigh scattering of hard x-rays

We report on the first elastic hard x-ray scattering experiment where the linear polarization characteristics of both the incident and the scattered radiation were observed. Rayleigh scattering was investigated in a relativistic regime by using a high-Z target material, namely gold, and a photon energy of 175 keV. Although the incident synchrotron radiation was nearly 100% linearly polarized, at a scattering angle of we observed a strong depolarization for the scattered photons with a degree of linear polarization of only. This finding agrees with second-order quantum electrodynamics calculations of Rayleigh scattering, when taking into account a small polarization impurity of the incident photon beam which was determined to be close to 98%. The latter value was obtained independently from the elastic scattering by analyzing photons that were Compton-scattered in the target. Moreover, our results indicate that when relying on state-of-the-art theory, Rayleigh scattering could provide a very accurate method to diagnose polarization impurities in a broad region of hard x-ray energies.

FARADAY ROTATION MEASURE SYNTHESIS OF INTERMEDIATE REDSHIFT QUASARS AS A PROBE OF INTERVENING MATTER

ABSTRACT There is evidence that magnetized material along the line of sight to distant quasars is detectable in the polarization properties of the background sources. The polarization properties appear to be correlated with the presence of intervening Mg ii absorption, which is thought to arise in outflowing material from star forming galaxies. In order to investigate this further, we have obtained high spectral resolution polarization measurements, with the Very Large Array and the Australia Telescope Compact Array, of a set of 49 unresolved quasars for which we have high quality optical spectra. These enable us to produce a Faraday Depth spectrum for each source, using Rotation Measure (RM) Synthesis. Our new independent radio data confirms that interveners are strongly associated with depolarization. We characterize the complexity of the Faraday Depth spectrum using a number of parameters and show how these are related, or not, to the depolarization and to the presence of Mg ii absorption along the line of sight. We argue that complexity and structure in the Faraday Depth distribution likely arise from both intervening material and intrinsically to the background source and attempt to separate these. We find that the strong radio depolarization effects associated with intervening material at redshifts out to arise from inhomogeneous Faraday screens producing a dispersion in RM across individual sources of around 10 rad m−2. This is likely produced by disordered fields with strengths of at least 3 μG.

MAGNETIC FIELD DISORDER AND FARADAY EFFECTS ON THE POLARIZATION OF EXTRAGALACTIC RADIO SOURCES

ABSTRACT We present a polarization catalog of 533 extragalactic radio sources that have a 2.3 GHz total intensity above 420 mJy from the S-band Polarization All Sky Survey, S-PASS, with corresponding 1.4 GHz polarization information from the NRAO VLA Sky Survey, NVSS. We studied the selection effects and found that fractional polarization, π, of radio objects at both wavelengths depends on the spectral index, the source magnetic field disorder, the source size, and depolarization. The relationship between depolarization, spectrum, and size shows that depolarization occurs primarily in the source vicinity. The median of resolved objects in NVSS is approximately two times larger than that of unresolved sources. Sources with little depolarization are ∼2 times more polarized than both highly depolarized and re-polarized sources. This indicates that intrinsic magnetic field disorder is the dominant mechanism responsible for the observed low fractional polarization of radio sources at high frequencies. We predict that number counts from polarization surveys will be similar at 1.4 GHz and at 2.3 GHz, for fixed sensitivity, although ∼10% of all sources may currently be missing because of strong depolarization. Objects with typically have simple Faraday structures, so they are most useful for background samples. Almost half of flat-spectrum ( ) and ∼25% of steep-spectrum objects are re-polarized. Steep-spectrum, depolarized sources show a weak negative correlation of depolarization with redshift in the range 0 &lt; z &lt; 2.3. Previous non-detections of redshift evolution are likely due the inclusion of re-polarized sources as well.

A screen for constituents of motor control and decision making in Drosophila reveals visual distance-estimation neurons.

Climbing over chasms larger than step size is vital to fruit flies, since foraging and mating are achieved while walking. Flies avoid futile climbing attempts by processing parallax-motion vision to estimate gap width. To identify neuronal substrates of climbing control, we screened a large collection of fly lines with temporarily inactivated neuronal populations in a novel high-throughput assay described here. The observed climbing phenotypes were classified; lines in each group are reported. Selected lines were further analysed by high-resolution video cinematography. One striking class of flies attempts to climb chasms of unsurmountable width; expression analysis guided us to C2 optic-lobe interneurons. Inactivation of C2 or the closely related C3 neurons with highly specific intersectional driver lines consistently reproduced hyperactive climbing whereas strong or weak artificial depolarization of C2/C3 neurons strongly or mildly decreased climbing frequency. Contrast-manipulation experiments support our conclusion that C2/C3 neurons are part of the distance-evaluation system.

Dopamine D1 receptor modulation of calcium channel currents in horizontal cells of mouse retina.

Horizontal cells form the first laterally interacting network of inhibitory interneurons in the retina. Dopamine released onto horizontal cells under photic and circadian control modulates horizontal cell function. Using isolated, identified horizontal cells from a connexin-57-iCre × ROSA26-tdTomato transgenic mouse line, we investigated dopaminergic modulation of calcium channel currents (ICa) with whole cell patch-clamp techniques. Dopamine (10 μM) blocked 27% of steady-state ICa, an action blunted to 9% in the presence of the L-type Ca channel blocker verapamil (50 μM). The dopamine type 1 receptor (D1R) agonist SKF38393 (20 μM) inhibited ICa by 24%. The D1R antagonist SCH23390 (20 μM) reduced dopamine and SKF38393 inhibition. Dopamine slowed ICa activation, blocking ICa by 38% early in a voltage step. Enhanced early inhibition of ICa was eliminated by applying voltage prepulses to +120 mV for 100 ms, increasing ICa by 31% and 11% for early and steady-state currents, respectively. Voltage-dependent facilitation of ICa and block of dopamine inhibition after preincubation with a Gβγ-blocking peptide suggested involvement of Gβγ proteins in the D1R-mediated modulation. When the G protein activator guanosine 5'-O-(3-thiotriphosphate) (GTPγS) was added intracellularly, ICa was smaller and showed the same slowed kinetics seen during D1R activation. With GTPγS in the pipette, additional block of ICa by dopamine was only 6%. Strong depolarizing voltage prepulses restored the GTPγS-reduced early ICa amplitude by 36% and steady-state ICa amplitude by 3%. These results suggest that dopaminergic inhibition of ICa via D1Rs is primarily mediated through the action of Gβγ proteins in horizontal cells.

0291 : Mitochondrial permeability transition pore opening might contribute to ventricular arrhythmia maintenance

Calcium leak from the sarcoplasmic reticulum (SR) favors cardiac sudden death through a calcium overload mechanism. Here we investigate the crosstalk between the calcium overload SR-mediated and the mitochondrial permeability transition pore (mPTP) opening during a ventricular arrhythmic episode. a burst pacing protocol was developed to induce ventricular arrhythmia in the perfused rat heart. Surface electrocardiogram, left ventricular pressure, and oxygen consumption were monitored. Epicardial fluorescence was recorded from either a mitochondrial membrane potential dye or an intracellular calcium dye. ECG signals were used to assess both arrhythmia complexity and duration. Hearts were perfused with tacrolimus (FK506) alone or in combination with cyclosporin A (CsA) to promote SR calcium leak or inhibit mPTP, respectively. Prior to arrhythmia induction, FK506 promoted mitochondrial depolarization and intracellular calcium overload in a CsA-sensitive manner. More than 90% of hearts developed complex ventricular arrhythmias in the FK506 group and this was accompanied by a strong mitochondrial membrane depolarization. In contrast, in the FK506 + CsA group, 100% of the hearts spontaneously defibrillate after a few seconds of arrhythmias. In this group, following arrhythmia induction, mitochondrial depolarization amplitude, intracellular calcium overload and heart efficiency depression was decreased in comparison to the FK506 group. Here we suggest that the FK506-induced calcium overload promotes mitochondrial calcium accumulation and leads to mPTP opening. We propose that mPTP opening should be considered as an arrhythmogenic substrate. The author hereby declares no conflict of interest

Self-Assembled Monolayers of Perfluoroanthracenylaminoalkane Thiolates on Gold as Potential Electron Injection Layers.

As a material with relatively small band gap and low lying valence orbitals, perfluoroanthracene (PFA) is of interest for the modification of electrode surfaces, for example, as charge injection layers for n-type organic semiconductors. To covalently attach PFA in the form of self-assembled monolayers (SAMs), we developed a synthesis of derivatives with a sulfur termination, linked to the 2-position of the PFA moieties by an -NH- group and a short alkane chain with two and three methylene groups, respectively. Spectroscopic characterization of the SAMs reveals that the molecules adopt an almost upright orientation on the gold surface, with the packing density mostly determined by the steric demands of the PFA units. The number of the methylene groups in the -NH-alkyl linker has only a minor impact on the SAM structure because of the nonsymmetric attachment of the PFA units, which permits the compensation of the orientational constraints imposed by the bending potential. The investigated SAMs alter the work function of gold by +(0.59-0.64) eV, suggesting comparably strong depolarization effects, affecting the extent of the work function modification.

Singular observation of the polarization-conversion effect for a gammadion-shaped metasurface.

In this article, the polarization-conversion effects of a gammadion-shaped metasurface in transmission and reflection modes are discussed. In our experiment, the polarization-conversion effect of a gammadion-shaped metasurface is investigated because of the contribution of the phase and amplitude anisotropies. According to our experimental and simulated results, the polarization property of the first-order transmitted diffraction is dominated by linear anisotropy and has weak depolarization; the first-order reflected diffraction exhibits both linear and circular anisotropies and has stronger depolarization than the transmission mode. These results are different from previously published research. The Mueller matrix ellipsometer and polar decomposition method will aid in the investigation of the polarization properties of other nanostructures.

A synergistic blocking effect of Mg²⁺ and spermine on the inward rectifier K⁺ (Kir2.1) channel pore.

Inward rectifier K+ channels (Kir2.1) exhibit an extraordinary rectifying feature in the current–voltage relationship. We have previously showed that the bundle–crossing region of the transmembrane domain constitutes the crucial segment responsible for the polyamine block. In this study, we demonstrated that the major blocking effect of intracellular Mg2+ on Kir2.1 channels is also closely correlated with K+ current flow, and the coupled movements of Mg2+ and K+ seem to happen in the same flux–coupling segment of the pore as polyamines. With a preponderant outward K+ flow, intracellular Mg2+ would also be pushed to and thus stay at the outermost site of a flux–coupling segment in the bundle–crossing region of Kir2.1 channels to block the pore, although with a much lower apparent affinity than spermine (SPM). However, in contrast to the evident possibilities of outward exit of SPM through the channel pore especially during strong membrane depolarization, intracellular Mg2+ does not seem to traverse the Kir2.1 channel pore in any case. Intracellular Mg2+ and SPM therefore may have a synergistic action on the pore–blocking effect, presumably via prohibition of the outward exit of the higher–affinity blocking SPM by the lower–affinity Mg2+.

Voltage-Independent Inhibition of the Tetrodotoxin-Sensitive Sodium Currents by Oxotremorine and Angiotensin II in Rat Sympathetic Neurons.

Tetrodotoxin-sensitive Na(+) currents have been extensively studied because they play a major role in neuronal firing and bursting. In this study, we showed that voltage-dependent Na(+) currents are regulated in a slow manner by oxotremorine (oxo-M) and angiotensin II in rat sympathetic neurons. We found that these currents can be readily inhibited through a signaling pathway mediated by G proteins and phospholipase C (PLC) β1. This inhibition is slowly established, pertussis toxin-insensitive, partially reversed within tens of seconds after oxo-M washout, and not relieved by a strong depolarization, suggesting a voltage-insensitive mechanism of inhibition. Specificity of the M1 receptor was tested by the MT-7 toxin. Activation and inactivation curves showed no shift in the voltage dependency under the inhibition by oxo-M. This inhibition is blocked by a PLC inhibitor (U73122, 1-(6-{[(17β)-3-Methoxyestra-1,3,5(10)-trien-17-yl]amino}hexyl)-1H-pyrrole-2,5-dione), and recovery from inhibition is prevented by wortmannin, a PI3/4 kinase inhibitor. Hence, the pathway involves Gq/11 and is mediated by a diffusible second messenger. Oxo-M inhibition is occluded by screening phosphatidylinositol 4,5-bisphosphate (PIP2)-negative charges with poly-l-lysine and prevented by intracellular dialysis with a PIP2 analog. In addition, bisindolylmaleimide I, a specific ATP-competitive protein kinase C (PKC) inhibitor, rules out that this inhibition may be mediated by this protein kinase. Furthermore, oxo-M-induced suppression of Na(+) currents remains unchanged when neurons are treated with calphostin C, a PKC inhibitor that targets the diacylglycerol-binding site of the kinase. These results support a general mechanism of Na(+) current inhibition that is widely present in excitable cells through modulation of ion channels by specific G protein-coupled receptors.

Spontaneous and Voltage-Activated Elementary Calcium Release Events in Intact Skeletal Muscle Fibers Expressing the Embryonic CaV1.1 Splice Variant

The adult isoform of voltage-gated L-type calcium channel (CaV1.1a) opens slowly at strong depolarizations, its contribution to the calcium influx during an action potential is negligible in skeletal muscle. In contrast, calcium influx through the embryonic splice variant (CaV1.1e) substantially contributes to depolarization-induced calcium transients as this isoform displays an altered voltage-dependence and gating kinetics as compared to CaV1.1a. Utilizing a genetically modified mouse model (CaV1.1αE29), which exclusively expresses the embryonic CaV1.1e variant in adult muscle, spontaneous or depolarization-evoked calcium release events were recorded in enzymatically isolated, intact adult skeletal muscle fibers from the m. flexor digitorum brevis, using the fluorescent calcium probe Fluo-8 and the Zeiss Live fast confocal microscope equipped with an Axon Multiclamp 700b. The events occurred at preferred locations as the distribution of spark number in the given position was different from the theoretical Poisson distribution which represents random event occurrence. Calcium events with both short (spark-like, duration = 46.0±1.5 ms, n = 125) and long (ember-like, duratio n= 473±14 ms, n = 218) duration were present on the same cell. In addition, events with complex kinetics, including late openings within an event also appeared. Voltage-activated (500 ms long pulses to the threshold of SR calcium release) with similar properties were also observed.

A study of a sample of high rotation-measure AGNs through multifrequency single-dish observations

We characterised and studied, in the radio band, a sample of candidates of high Rotation Measure (RM). These point-like objects show a strong depolarisation at 21cm. This feature suggests the presence of a very dense medium surrounding them in a combination of a strong magnetic field. This work aims at selecting and studying a sample of radio sources with high RM, thus to study their physical conditions and their status with respect to their surrounding medium. We want to understand if any connection is present between the AGN hosting galaxy medium with some evolutionary track and/or some restarting phase of the AGN itself. Multifrequency single-dish observations were performed with the 100-m Effelsberg telescope to define the initial sample, to characterise the SED of the final sample (30 targets) and to determine their RM in the 11 to 2 cm wavelength range. From the observations, the SED together with polarisation information, i.e. the fractional polarisation and the polarisation angle, have been determined. Three different object types were revealed from the SEDs analysis: Older, GPS-like and Mixed. For each of the targets, the rotation measure has been found and the depolarisation has been modelled. No significant correlation have been found between the depolarisation behaviours and the SEDs, while a correlation has been found between sources with mixed SED (with an old component at low frequency and compact components at high frequencies) and high values of the rotation measure (with values in the rest frame larger than 1000 rad/m^2). This work helps us to define and identify a sample of sources with high RM. From the analysis we can conclude that the sources showing a restarting phase at high frequency (with a Mixed SED), are characterised by a really dense and/or a magnetised medium that strongly rotates the polarisation angle at the different frequencies, leading to a high RM.