bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hypokalaemia induces Ca2+ overload and Ca2+ waves in ventricular myocytes by reducing Na+,K+‐ATPase α2 activity
Authors: Aronsen J. M. , Skogestad J. , Lewalle A. , Louch W. E. , Hougen K. , Stokke M. K. , Swift F. , Niederer S. , Smith N. P. , Sejersted O. M. , Sjaastad I. 
Published: October 2014

Key points
Hypokalaemia is a risk factor for development of ventricular arrhythmias.
In rat ventricular myocytes, low extracellular K+ (corresponding to clinical moderate hypokalaemia) increased Ca2+ wave probability, Ca2+ transient amplitude, sarcoplasmic reticulum (SR) Ca2+ load and induced SR Ca2+ leak.
Low extracellular K+ reduced Na+,K+‐ATPase (NKA) activity and hyperpolarized the resting membrane potential in ventricular myocytes. Both experimental data and modelling indicate that reduced NKA activity and subsequent Na+ accumulation sensed by the Na+, Ca2+ exchanger (NCX) lead to increased Ca2+ transient amplitude despite concomitant hyperpolarization of the resting membrane potential.
Low extracellular K+ induced Ca2+ overload by lowering NKA α2 activity. Triggered ventricular arrhythmias in patients with hypokalaemia may therefore be attributed to reduced NCX forward mode activity linked to an effect on the NKA α2 isoform.
AbstractHypokalaemia is a risk factor for development of ventricular arrhythmias. The aim of this study was to determine the cellular mechanisms leading to triggering of arrhythmias in ventricular myocytes exposed to low Ko. Low Ko, corresponding to moderate hypokalaemia, increased Ca2+ transient amplitude, sarcoplasmic reticulum (SR) Ca2+ load, SR Ca2+ leak and Ca2+ wave probability in field stimulated rat ventricular myocytes. The mechanisms leading to Ca2+ overload were examined. Low Ko reduced Na+,K+‐ATPase (NKA) currents, increased cytosolic Na+ concentration and increased the Na+ level sensed by the Na+, Ca2+ exchanger (NCX). Low Ko also hyperpolarized the resting membrane potential (RMP) without significant alterations in action potential duration. Experiments in voltage clamped and field stimulated ventricular myocytes, along with mathematical modelling, suggested that low Ko increases the Ca2+ transient amplitude by reducing NKA activity despite hyperpolarization of the RMP. Selective inhibition of the NKA α2 isoform by low dose ouabain abolished the ability of low Ko to reduce NKA currents, to increase Na+ levels sensed by NCX and to increase the Ca2+ transient amplitude. We conclude that low Ko, within the range of moderate hypokalaemia, increases Ca2+ levels in ventricular myocytes by reducing the pumping rate of the NKA α2 isoform with subsequent Na+ accumulation sensed by the NCX. These data highlight reduced NKA α2‐mediated control of NCX activity as a possible mechanism underlying triggered ventricular arrhythmias in patients with hypokalaemia.
GABAB receptor‐mediated tonic inhibition regulates the spontaneous firing of locus coeruleus neurons in developing rats and in citalopram‐treated rats
Authors: Wang Han‐Ying , Kuo Zhao‐Chen , Fu Yu‐Show , Chen Ruei‐Feng , Min Ming‐Yuan , Yang Hsiu‐Wen 
Published: October 2014

Key points
Noradrenaline (NA)‐releasing neurons in the locus coeruleus (LC) provide NA to the forebrain and play important roles in regulating many brain functions.
LC neurons are subject to tonic inhibition mediated by GABAB receptors (GABABRs) and that the extent of the effect varies with ambient GABA levels.
GABABR‐mediated tonic inhibition can effectively tune the spontaneous firing rate (SFR) of LC neurons; it is developmentally regulated and is responsible for maintaining a constant SFR of LC neurons during development.
In male, but not female rats, chronic perinatal treatment with citalopram, a selective serotonin reuptake inhibitor, results in downregulation of GABABR‐mediated tonic inhibition of LC neurons that partially accounts for increased SFR in male, but not female, rats receiving such treatment.
Our results show that GABABR‐mediated tonic inhibition could be an important player in the development of normal and abnormal behaviours/brain functions associated with the LC–NA system.
AbstractNoradrenaline (NA)‐releasing neurons in the locus coeruleus (LC) provide NA to the forebrain. Their activity is believed to be a key factor regulating the wakefulness/arousal level of the brain. In this study, we found that the activity of NA‐releasing neurons in the LC (LC neurons) was subject to γ‐aminobutyric acid (GABA) tonic inhibition through GABAB receptors (GABABRs), but not GABAA receptors. The intensity of GABABR tonic inhibition was found to depend on ambient GABA levels, as it was dramatically increased by blockade of GABA reuptake. It also varied with the function of GABABRs. The GABABR activity on LC neurons was found to increase with postnatal age up to postnatal days 8–10, resulting in increased tonic inhibition. Interestingly, there was no significant difference in the spontaneous activity of LC neurons at different postnatal ages unless GABABR tonic inhibition was blocked. These results show that, during postnatal development, there is a continuous increase in GABABR tonic inhibition that maintains the activity of LC neurons at a proper level. In male, but not female, rats, chronic perinatal treatment with citalopram, a selective serotonin reuptake inhibitor, reduced GABABR activity and tonic inhibition, which might result in the significantly higher spontaneous activity of LC neurons seen in these animals. In conclusion, our results show that GABABR‐mediated tonic inhibition has a direct impact on the spontaneous activity of LC neurons and that the extent of the effect varies with ambient GABA levels and functionality of GABABR signalling.
Effect of improved TLD dosimetry on the determination of dose rate constants for 125I and 103Pd brachytherapy seeds
Authors: Rodriguez M. , Rogers D. W. O. 
Published: October 2014

Purpose:To more accurately account for the relative intrinsic energy dependence and relative absorbed‐dose energy dependence of TLDs when used to measure dose rate constants (DRCs) for 125I and 103Pd brachytherapy seeds, to thereby establish revised “measured values” for all seeds and compare the revised values with Monte Carlo and consensus values.Methods:The relative absorbed‐dose energy dependence, frel, for TLDs and the phantom correction, Pphant, are calculated for 125I and 103Pd seeds using the EGSnrc BrachyDose and DOSXYZnrc codes. The original energy dependence and phantom corrections applied to DRC measurements are replaced by calculated (frel)−1 and Pphant values for 24 different seed models. By comparing the modified measured DRCs to the MC values, an appropriate relative intrinsic energy dependence, , is determined. The new Pphant values and relative absorbed‐dose sensitivities, , calculated as the product of (frel)−1 and , are used to individually revise the measured DRCs for comparison with Monte Carlo calculated values and TG‐43U1 or TG‐43U1S1 consensus values.Results:In general, frel is sensitive to the energy spectra and models of the brachytherapy seeds. Values may vary up to 8.4% among 125I and 103Pd seed models and common TLD shapes. Pphant values depend primarily on the isotope used. Deduced values are 1.074 ± 0.015 and 1.084 ± 0.026 for 125I and 103Pd seeds, respectively. For (1 mm)3 chips, this implies an overall absorbed‐dose sensitivity relative to 60Co or 6 MV calibrations of 1.51 ± 1% and 1.47 ± 2% for 125I and 103Pd seeds, respectively, as opposed to the widely used value of 1.41. Values of Pphant calculated here have much lower statistical uncertainties than literature values, but systematic uncertainties from density and composition uncertainties are significant. Using these revised values with the literature's DRC measurements, the average discrepancies between revised measured values and Monte Carlo values are 1.2% and 0.2% for 125I and 103Pd seeds, respectively, compared to average discrepancies for the original measured values of 4.8%. On average, the revised measured values are 4.3% and 5.9% lower than the original measured values for 103Pd and 125I seeds, respectively. The average of revised DRCs and Monte Carlo values is 3.8% and 2.8% lower for 125I and 103Pd seeds, respectively, than the consensus values in TG‐43U1 or TG‐43U1S1.Conclusions:This work shows that frel is TLD shape and seed model dependent suggesting a need to update the generalized energy response dependence, i.e., relative absorbed‐dose sensitivity, measured 25 years ago and applied often to DRC measurements of 125I and 103Pd brachytherapy seeds. The intrinsic energy dependence for LiF TLDs deduced here is consistent with previous dosimetry studies and emphasizes the need to revise the DRC consensus values reported by TG‐43U1 or TG‐43U1S1.
Benchmarking of a treatment planning system for spot scanning proton therapy: Comparison and analysis of robustness to setup errors of photon IMRT and proton SFUD treatment plans of base of skull meningioma
Authors: Harding R. , Trnková P. , Weston S. J. , Lilley J. , Thompson C. M. , Short S. C. , Loughrey C. , Cosgrove V. P. , Lomax A. J. , Thwaites D. I. 
Published: October 2014

Purpose:Base of skull meningioma can be treated with both intensity modulated radiation therapy (IMRT) and spot scanned proton therapy (PT). One of the main benefits of PT is better sparing of organs at risk, but due to the physical and dosimetric characteristics of protons, spot scanned PT can be more sensitive to the uncertainties encountered in the treatment process compared with photon treatment. Therefore, robustness analysis should be part of a comprehensive comparison between these two treatment methods in order to quantify and understand the sensitivity of the treatment techniques to uncertainties. The aim of this work was to benchmark a spot scanning treatment planning system for planning of base of skull meningioma and to compare the created plans and analyze their robustness to setup errors against the IMRT technique.Methods:Plans were produced for three base of skull meningioma cases: IMRT planned with a commercial TPS [Monaco (Elekta AB, Sweden)]; single field uniform dose (SFUD) spot scanning PT produced with an in‐house TPS (PSI‐plan); and SFUD spot scanning PT plan created with a commercial TPS [XiO (Elekta AB, Sweden)]. A tool for evaluating robustness to random setup errors was created and, for each plan, both a dosimetric evaluation and a robustness analysis to setup errors were performed.Results:It was possible to create clinically acceptable treatment plans for spot scanning proton therapy of meningioma with a commercially available TPS. However, since each treatment planning system uses different methods, this comparison showed different dosimetric results as well as different sensitivities to setup uncertainties. The results confirmed the necessity of an analysis tool for assessing plan robustness to provide a fair comparison of photon and proton plans.Conclusions:Robustness analysis is a critical part of plan evaluation when comparing IMRT plans with spot scanned proton therapy plans.
Asymmetric dose–volume optimization with smoothness control for rotating‐shield brachytherapy
Authors: Liu Yunlong , Flynn Ryan T. , Kim Yusung , Wu Xiaodong 
Published: October 2014

Purpose:It is important to reduce fluence map complexity in rotating‐shield brachytherapy (RSBT) inverse planning to improve delivery efficiency while maintaining plan quality. This study proposes an efficient and effective RSBT dose optimization method which enables to produce smooth fluence maps.Methods:Five cervical cancer patients each with a high‐risk clinical‐target‐volume (HR‐CTV) larger than 40 cm3 were considered as the test cases. The RSBT source was a partially shielded electronic brachytherapy source (Xoft Axxent™). The anchor RSBT plans generated by the asymmetric dose–volume optimization with smoothness control (ADOS) method were compared against those produced by the dose–surface optimization (DSO) method and inverse‐planning with simulated annealing (IPSA). Either L1‐norm or L2‐norm was used to measure the smoothness of a fluence map in the proposed ADOS method as one weighted term of the objective function. Uniform dwell‐time scaling was applied to all plans such that HR‐CTV D90 was maximized without violating the D2cc tolerances of the rectum, bladder, and sigmoid colon. The quality of the anchor plans was measured with HR‐CTV D90 of the anchor plans. Single‐shielded RSBT [(S‐RSBT), RSBT with single, fix sized delivery window] and dynamic‐sheilded RSBT [(D‐RSBT), RSBT with dynamically varying sized delivery window] delivery plans generated based on the anchor plans were also measured, with delivery time constraints of 10, 20, and 30 min/fraction (fx).Results:The average HR‐CTV D90 values of the anchor plans achieved by the ADOS, DSO, and IPSA methods were 111.5, 94.2, and 107.4 Gy, respectively, where the weighting parameter β used in ADOS with L2‐norm was set to be 100. By using S‐RSBT sequencing and 20 min/fx delivery time, the corresponding D90 values were 88.8, 81.9, and 83.4 Gy; while using D‐RSBT sequencing with 20 min/fx delivery time, the corresponding D90 values were 91.4, 88.3, and 78.9 Gy, respectively. The average optimization times for ADOS, DSO, and IPSA were, respectively, 77, 4, and 1800 s. By using L1‐norm instead of L2‐norm in the ADOS method, the optimization time was increased by 20 s, while the D90 was reduced by 6.8 Gy on average. ADOS‐L1 was found to be more sensitive to the weighting parameter than ADOS‐L2. If β was increased to 10 000, the D90 drop with ADOS‐L1 was 38 Gy, while the drop with ADOS‐L2 is 13 Gy.Conclusions:The ADOS method had a reasonable optimization time cost, while achieving comparable RSBT dose plans as the IPSA method, which is of much higher time complexity. Compared to the DSO and IPSA methods, ADOS is able to generate anchor plans which are more suitable for RSBT delivery while preserving the high quality of the original plans. Compared to ADOS‐L1, ADOS‐L2 is able to achieve better quality of anchor plans more efficiently.
Predation by Myxococcus xanthus Induces Bacillus subtilis To Form Spore-Filled Megastructures
Authors: Müller Susanne , Strack Sarah N. , Ryan Sarah E. , Kearns Daniel B. , Kirby John R. 
Published: October 2014

ABSTRACT

Biofilm formation is a common mechanism for surviving environmental stress and can be triggered by both intraspecies and interspecies interactions. Prolonged predator-prey interactions between the soil bacterium
Myxococcus xanthus
and
Bacillus subtilis
were found to induce the formation of a new type of
B. subtilis
biofilm, termed megastructures. Megastructures are tree-like brachiations that are as large as 500 μm in diameter, are raised above the surface between 150 and 200 μm, and are filled with viable endospores embedded within a dense matrix. Megastructure formation did not depend on TasA, EpsE, SinI, RemA, or surfactin production and thus is genetically distinguishable from colony biofilm formation on MSgg medium. As
B. subtilis
endospores are not susceptible to predation by
M. xanthus
, megastructures appear to provide an alternative mechanism for survival. In addition,
M. xanthus
fruiting bodies were found immediately adjacent to the megastructures in nearly all instances, suggesting that
M. xanthus
is unable to acquire sufficient nutrients from cells housed within the megastructures. Lastly, a
B. subtilis
mutant lacking the ability to defend itself via bacillaene production formed megastructures more rapidly than the parent. Together, the results indicate that production of the megastructure facilitates
B. subtilis
escape into dormancy via sporulation.
Siderophore-Mediated Iron Acquisition Influences Motility and Is Required for Full Virulence of the Xylem-Dwelling Bacterial Phytopathogen Pantoea stewartii subsp. stewartii
Authors: Burbank Lindsey , Mohammadi Mojtaba , Roper M. Caroline 
Published: October 2014

ABSTRACT

Iron is a key micronutrient for microbial growth but is often present in low concentrations or in biologically unavailable forms. Many microorganisms overcome this challenge by producing siderophores, which are ferric-iron chelating compounds that enable the solubilization and acquisition of iron in a bioactive form.
Pantoea
stewartii
subsp.
stewartii
, the causal agent of Stewart's wilt of sweet corn, produces a siderophore under iron-limiting conditions. The proteins involved in the biosynthesis and export of this siderophore are encoded by the
iucABCD-iutA
operon, which is homologous to the aerobactin biosynthetic gene cluster found in a number of enteric pathogens. Mutations in
iucA
and
iutA
resulted in a decrease in surface-based motility that
P. stewartii
utilizes during the early stages of biofilm formation, indicating that active iron acquisition impacts surface motility for
P. stewartii
. Furthermore, bacterial movement
in planta
is also dependent on a functional siderophore biosynthesis and uptake pathway. Most notably, siderophore-mediated iron acquisition is required for full virulence in the sweet corn host, indicating that active iron acquisition is essential for pathogenic fitness for this important xylem-dwelling bacterial pathogen.
Transmission and Persistence of Livestock-Associated Methicillin-Resistant Staphylococcus aureus among Veterinarians and Their Household Members
Authors: Bosch T. , Verkade E. , van Luit M. , Landman F. , Kluytmans J. , Schouls L. M. 
Published: October 2014

ABSTRACT

After the first isolation of livestock-associated methicillin-resistant
Staphylococcus aureus
(LA-MRSA) in 2003, this MRSA variant quickly became the predominant MRSA obtained from humans as part of the Dutch national MRSA surveillance. Previous studies have suggested that human-to-human transmission of LA-MRSA, compared to that of other MRSA lineages, rarely occurs. However, these reports describe the transmission of LA-MRSA based on epidemiology and limited molecular characterization of isolates, making it difficult to assess whether transmission actually occurred. In this study, we used whole-genome maps (WGMs) to identify possible transmission of LA-MRSA between humans. For this, we used LA-MRSA isolates originating from a 2-year prospective longitudinal cohort study in which livestock veterinarians and their household members were repeatedly sampled for the presence of
S. aureus
. A considerable degree of genotypic variation among LA-MRSA strains was observed. However, there was very limited variability between the maps of the isolates originating from the same veterinarian, indicating that each of the veterinarians persistently carried or had reacquired the same LA-MRSA strain. Comparison of WGMs revealed that LA-MRSA transmission had likely occurred within virtually every veterinarian household. Yet only a single LA-MRSA strain per household appeared to be involved in transmission. The results corroborate our previous finding that LA-MRSA is genetically diverse. Furthermore, this study shows that transmission of LA-MRSA between humans occurs and that carriage of LA-MRSA can be persistent, thus posing a potential risk for spread of this highly resistant pathogen in the community.
A Polysaccharide Utilization Locus from an Uncultured Bacteroidetes Phylotype Suggests Ecological Adaptation and Substrate Versatility
Authors: Mackenzie A. K. , Naas A. E. , Kracun S. K. , Schückel J. , Fangel J. U. , Agger J. W. , Willats W. G. T. , Eijsink V. G. H. , Pope P. B. 
Published: October 2014

ABSTRACT

Recent metagenomic analyses have identified uncultured bacteria that are abundant in the rumen of herbivores and that possess putative biomass-converting enzyme systems. Here we investigate the saccharolytic capabilities of a polysaccharide utilization locus (PUL) that has been reconstructed from an uncultured
Bacteroidetes
phylotype (SRM-1) that dominates the rumen microbiome of Arctic reindeer. Characterization of the three PUL-encoded outer membrane glycoside hydrolases was performed using chromogenic substrates for initial screening, followed by detailed analyses of products generated from selected substrates, using high-pressure anion-exchange chromatography with electrochemical detection. Two glycoside hydrolase family 5 (GH5) endoglucanases (GH5_g and GH5_h) demonstrated activity against β-glucans, xylans, and xyloglucan, whereas GH5_h and the third enzyme, GH26_i, were active on several mannan substrates. Synergy experiments examining different combinations of the three enzymes demonstrated limited activity enhancement on individual substrates. Binding analysis of a SusE-positioned lipoprotein revealed an affinity toward β-glucans and, to a lesser extent, mannan, but unlike the two SusD-like lipoproteins previously characterized from the same PUL, binding to cellulose was not observed. Overall, these activities and binding specificities correlated well with the glycan content of the reindeer rumen, which was determined using comprehensive microarray polymer profiling and showed an abundance of various hemicellulose glycans. The substrate versatility of this single PUL putatively expands our perceptions regarding PUL machineries, which so far have demonstrated gene organization that suggests one cognate PUL for each substrate type. The presence of a PUL that possesses saccharolytic activity against a mixture of abundantly available polysaccharides supports the dominance of SRM-1 in the Svalbard reindeer rumen microbiome.
Novel Mechanism Coupling Cyclic AMP-Protein Kinase A Signaling and Golgi Trafficking via Gyp1 Phosphorylation in Polarized Growth
Authors: Huang Zhen-Xing , Wang Haitao , Wang Yan-Ming , Wang Yue 
Published: October 2014

ABSTRACT

The cyclic AMP (cAMP)-protein kinase A (PKA) signaling activates virulence expression during hyphal development in the fungal human pathogen
Candida albicans
. The hyphal growth is characterized by Golgi polarization toward the hyphal tips, which is thought to enhance directional vesicle transport. However, how the hypha-induction signal regulates Golgi polarization is unknown. Gyp1, a Golgi-associated protein and the first GTPase-activating protein (GAP) in the Rab GAP cascade, critically regulates membrane trafficking from the endoplasmic reticulum to the plasma membrane. Here, we report a novel pathway by which the cAMP-PKA signaling triggers Golgi polarization during hyphal growth. We demonstrate that Gyp1 plays a crucial role in actin-dependent Golgi polarization. Hyphal induction activates PKA, which in turn phosphorylates Gyp1. Phosphomimetic mutation of four PKA sites identified by mass spectrometry (Gyp1
4E
) caused strong Gyp1 polarization to hyphal tips, whereas nonphosphorylatable mutations (Gyp1
4A
) abolished it. Gyp1
4E
exhibited enhanced association with the actin motor Myo2, while Gyp1
4A
showed the opposite effect, providing a possible mechanism for Golgi polarization. A GAP-dead Gyp1 (Gyp1
R292K
) showed strong polarization similar to that seen with Gyp1
4E
, indicating a role for the GAP activity. Mutating the PKA sites on Gyp1 also impaired the recruitment of a late Golgi marker, Sec7. Furthermore, proper PKA phosphorylation and GAP activity of Gyp1 are required for virulence in mice. We propose that the cAMP-PKA signaling directly targets Gyp1 to promote Golgi polarization in the yeast-to-hypha transition, an event crucial for
C. albicans
infection.