145 research outputs found

    Density dependence of the pairing interaction and pairing correlation in unstable nuclei

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    This work aims at a global assessment of the effect of the density dependence of the zero-range pairing interaction. Systematic Skyrme-Hartree-Fock-Bogoliubov calculations with the volume, surface and mixed pairing forces are carried out to study the pairing gaps in even-even nuclei over the whole nuclear chart. Calculations are also done in coordinate representation for unstable semi-magic even-even nuclei. The calculated pairing gaps are compared with empirical values from four different odd-even staggering formulae. Calculations with the three pairing interactions are comparable for most nuclei close to β\beta-stability line. However, the surface interaction calculations predict neutron pairing gaps in neutron-rich nuclei that are significantly stronger than those given by the mixed and volume pairing. On the other hand, calculations with volume and mixed pairing forces show noticeable reduction of neutron pairing gaps in nuclei far from the stability.Comment: 9 pages, 10 figures, 3 tables, printer-friendl

    Age-dependent dynamic electrophysiological field potential behavior of atrioventricular node during experimental AF in rabbit

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    Introduction: Electrophysiological studies have demonstrated a relationship between aging and atrioventricular (AV) nodal conduction and refractoriness. The aim of the present study was to determine the effects of nodal aging on dynamic AV nodal field potential recording during atrial fibrillation (AF) in rabbit. Methods: Two groups of male New Zealand rabbits (neonatal 2-week-olds and adult 12-week-olds, n=14 each group) were used in this study. Field potential recordings were executed by silver electrodes with a diameter of 100 μM. Pre-defined stimulation protocols of AF, zone of concealment (ZOC) and concealed conduction for determination of the electrophysiological properties of the AV-node were separately applied in each group. Results: Results of the study showed that mean ventricular rate (HH) during atrial fibrillation was smaller in the neonatal compared to the adult group (229.1 ± 8.3 versus 198.6 ± 13.1 msec, respectively). Also ventricular distribution conduction pattern showed two peaks in the adult and one peak in the neonatal group. Analyzing the zone of concealment in different rates and after concealed beat indicated that the zone of concealment in neonates were significantly smaller compared with adult rabbits and increasing zone of concealment, which is accompanied with increasing ventricular rate is abrogated in the neonatal group (5 ± 3.3, 12.2 ± 6.3 msec). Conclusion: The results of this study showed that the electrophysiological protective dynamic behavior of the AV node during atrial fibrillation is smaller in neonates compared to adults. Narrower zone of concealment, abrogation rate dependent trend of the zone of concealment and shorter nodal refractoriness can account for the specific nodal electrophysiological properties of neonatal rabbits

    Effect of nitric oxide modulation on the basic and rate-dependent electrophysiological properties of AV-node in the isolated heart of rabbit: The role of adrenergic and cholinergic receptors

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    Introduction: Recent studies showed that nitrergic system have specific modulatory effects on electrophysiological properties of atrioventricular (AV) node. The aim of this study was to determine the effects of nitric oxide (NO) on the electrophysiological properties of isolated rabbit AV node and to investigate the role of adrenergic and cholinergic receptors in the mechanism of its action. Methods: In our laboratory, an experimental model of isolated double-perfused AV-node of rabbits weighing 1.5-2 kg was used. Specific experimental protocols of recovery, Facilitation, Fatigue and Wenckbach were applied in both control and in the presence of the drug. A total number of 35 rabbits were divided randomly into the following groups (n=7): 1) L-Arg (NO donor) (250, 750 and 1000 μmol), 2) L- NAME, a NO synthesis inhibitor (25, 50 and 100 μmol), 3) L-Arg + L- NAME, 4) Nadolol (1 μmol), 5) Atropine (3 μmol). All data were shown as mean ± SE. The level of statistical significance was set at p<0.05. Results: Our results revealed the depressant effect of L-Arg on the basic and rate-dependent electrophysiological properties of AV-node. L- NAME did not deteriorate the effects of L-Arg on the basic and rate-dependent properties, nevertheless, at high concentration (100 μmol) it had a direct inhibitory effect on the AV-node. Nadolol and atropine could prevent the effects of NO on the basic nodal characteristics and the fatigue phenomenon, respectively. Conclusion: Nitergic system can affect basic and rate-dependent electrophysiological properties of the AV-node through adrenergic and cholinergic receptors

    Rate-dependent and antiarrhythmic reentrant tachycardia (AVNRT) effects of simvastatin in isolated rabbit atrioventricular nodal model

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    Background and purpose: Several previous studies have shown the direct and indirect effects of statins on supraventricular and ventricular arrhythmia. The purpose of the present study is to determine (1) whether Simvastatin modifies the rate-dependent properties of the AV node, (2) to what extent such changes are related to effect of Simvastatin on the basic properties of AV nodal conduction and refractoriness. Materials and methods: AV nodal refractoriness (AVERP & AVFRP) and rate dependency protocols Fatigue and Facilitation were used to assesse the electrophysiological properties of AV node. We used an isolated perfussed rabbit with AV nodal preparation in one group (N=8). The stimulation protocols were carried out during control phase and in the presence of various concentrations of Simvastatin (0.5 , 0.8 , 1, 3 ,10 μm). Results: Simvastatin in concentration-dependent manner successfully prolonged effective and functional nodal refractory period (AVERP & AVFRP). Also an increase in Wenckebach cycle length was observed. Simvastatin in high concentration (3,10 μm) increases the arrhythmia threshold. Various concentrations of simvastatin increased fatigue, but it reached to significant level only at 30 μM. Conclusion: Simvastatin has potential anti-AVNRT effects by elevating arrhythmia threshold and prolongation of nodal refractoriness

    Role of nitric oxide on the electrophysiological properties of isolated rabbit atrioventricular node by extracellular field potential during atrial fibrillation

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    Introduction: The aim of the present study was to determine direct effects of NO modulation on protective electrophysiological properties of atrioventricular node (AV node) in the experimental model of AF in rabbit. Methods: Isolated perfused rabbit AV nodal preparations were used in two groups. In the first group (N=7), LNAME (50μM) was applied. In the second group (N=12), different concentrations of L - argenine (250 μM - 5000 μM) were added to the solution. Programmed stimulation protocols were used to quantify AV nodal conduction time, refractoriness and zone of concealment. AF protocol was executed by software with coupling intervals (ranging from 75–125 msec). Results: L-NAME had depressive effects on basic AV nodal properties. L-Arginine (250μM) had direct inhibitory effects on nodal conduction time, Wenckebach and refractoriness. Significant increases in the number of concealed beats were induced by L-Arginine (500 μM). Number of concealed beats were increased from 700.7±33.7 to 763±21 msec (P<0.05). Trend of zone of concealment prolongation in a frequency-dependent model was abrogated by Larginine (250, 5000 μM). Conclusion: NO at low concentration (in the presence of L-NAME) had facilitatory role on AV nodal properties, but at high concentration (in the presence of L-arginine) enhanced protective role of AV node during AF. Biphasic modulatory role of NO may affect protective behavior of AV node during AF. © 2011, Iranian Society of Physiology and Pharmacology. All rights reserved

    Enhanced radiosensitivity of LNCaP prostate cancer cell line by gold-photoactive nanoparticles modified with folic acid

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    Background: Conventional cancer treatment methods suffer from many limitations such as non-specificity in discrimination between healthy and malignant cells. The aim of this study was to investigate the role of polymeric gold-photoactive nanoparticles (PGPNPs) conjugated with folic acid (FA) as theranostic nanoparticles for active targeting, real-time fluorescence tracing and radiosensitivity inducition in LNCaP prostate cancer cells. Methods: The cellular uptake and cytotoxicity effect of gold nanoparticles (PGPNPs and PGPNPs-FA) after 2 and 24 h treatment were evaluated in in both cancer (LNCaP) and normal (HUVEC) cells using fluorescent microscopy, Induced coupled plasma optical emission spectrometry (ICP-OES) and Tetrazolium bromide dye (MTT), respectively. The therapeutic efficacy was analyzed on the LNCaP cells. For this purpose, LNCaP cells were treated by nanoparticles and ionizing radiation, and the synergistic effect of treatment methods were evaluated by colony formation assay (CFA) and Flow cytometry analysis. Results: The results of fluorescence imaging and ICP-OES data showed that the LNCaP cells absorbed PGPNP-FA nanoparticles more than PGPNP (P < 0.001). Also, the uptake of nanoparticles was significantly greater in cancer cells than in healthy ones (P < 0.01). MTT assay results indicated higher cytotoxic effect of nanoparticles conjugated with FA in folate-receptor overexpressing LNCaP cancer cells compared to HUVEC normal cells (P < 0.01). Furthermore, CFA and Flow cytometry results demonstrated that combinatorial therapy of polymeric gold nanoparticles with/without FA and ionizing radiation at various doses (2, 4 and 6 Gy) had a synergistic effect on survival fraction and induction of apoptotic and necrotizing cell death (P < 0.01). Conclusion: PGPNPs-FA nanoparticles led to higher and more specific uptake and accumulation of nanoparticles in LNCaP cells, thereby increasing the ability of gold nanoparticles as radio-sensitizer. © 2019 Elsevier B.V

    Local biases drive, but do not determine, the perception of illusory trajectories

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    When a dot moves horizontally across a set of tilted lines of alternating orientations, the dot appears to be moving up and down along its trajectory. This perceptual phenomenon, known as the slalom illusion, reveals a mismatch between the veridical motion signals and the subjective percept of the motion trajectory, which has not been comprehensively explained. In the present study, we investigated the empirical boundaries of the slalom illusion using psychophysical methods. The phenomenon was found to occur both under conditions of smooth pursuit eye movements and constant fixation, and to be consistently amplified by intermittently occluding the dot trajectory. When the motion direction of the dot was not constant, however, the stimulus display did not elicit the expected illusory percept. These findings confirm that a local bias towards perpendicularity at the intersection points between the dot trajectory and the tilted lines cause the illusion, but also highlight that higher-level cortical processes are involved in interpreting and amplifying the biased local motion signals into a global illusion of trajectory perception
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