Redox regulation of the calcium activated and voltage gated potassium channel, BK: shaping the pancreatic beta cells action potential and calcium influx

Large conductance calcium activated potassium channels (BK) are ubiquitous in the membranes of all excitable cells and are responsible for limiting action potential propagation and cell function by hyperpolarising action potentials, there is evidence that BK channels are important for the function of pancreatic β cells. Hydrogen peroxide (H2O2) is a reactive oxygen species commonly found in all cell types and known to have an effect on BK channels. In this study electrophysiology and fluorescence imaging were used determine the effect of hydrogen peroxide on BK channel activity and action potential shaping. In single-channel patches BK channels were activated by hydrogen peroxide with a bell-shaped relationship, 1 µM H2O2 was shown to be the most stimulatory concentration, identified by a 1000-fold increase in open channel probability (p = 0.0280). From whole-cell recordings, carried out to confirm activity across the whole cell and measure the voltage dependent effects, it was shown that this was a universal effect across the entire cell membrane with a 24% increase in potassium current amplitude (p = 0.0224), the effect of hydrogen peroxide acting on BK was confirmed by the blockers quinine and paxilline. Inside-out patch showed that hydrogen peroxide acted directly on channels to stimulate channel opening (p = 0.0141). Current-clamp recordings showed that hydrogen peroxide had no significant effect on the shape of action potentials in terms of baseline membrane potential, peak amplitude; half-width and maximum rate of decay of spiking, stimulated by 2.5 and 10 mM glucose. Through calcium imaging it was observed that H2O2 had no significant effect on calcium influx. It was concluded that although hydrogen peroxide directly activates BK channels in β cells, this effect is insufficient to alter the shape of glucose-stimulated action potentials or calcium influx

Simvastatin inhibits L-type Ca2+-channel activity through impairment of mitochondrial function

© The Author(s) 2019. Published by Oxford University Press on behalf of the Society of Toxicology. Plasma membrane ion channels and mitochondrial electron transport complexes (mETC) are recognized "off targets" for certain drugs. Simvastatin is one such drug, a lipophilic statin used to treat hypercholesterolemia, but which is also associated with adverse effects like myopathy and increased risk of glucose intolerance. Such myopathy is thought to arise through adverse actions of simvastatin on skeletal muscle mETC and mitochondrial respiration. In this study, we investigated whether the glucose intolerance associated with simvastatin is also mediated via adverse effects on mETC in pancreatic beta-cells because mitochondrial respiration underlies insulin secretion from these cells, an effect in part mediated by promotion of Ca2+ influx via opening of voltage-gated Ca2+ channels (VGCCs). We used murine pancreatic beta-cells to investigate these ideas. Mitochondrial membrane potential, oxygen consumption, and ATP-sensitive-K+- channel activity were monitored as markers of mETC activity, respiration, and cellular ATP/ADP ratio respectively; Ca2+ channel activity and Ca2+ influx were also measured. In intact beta-cells, simvastatin inhibited oxidative respiration (IC50 approximately 3 mM) and mETC (1 0.1 mM reversed activation of VGCCs by glucose but had no significant effect in the sugar s absence. The VGCC effects were mimicked by rotenone which also decreased respiration and ATP/ADP. This study demonstrates modulation of beta-cell VGCC activity by mitochondrial respiration and their sensitivity to mETC inhibitors. This reveals a novel outcome for the action of drugs like simvastatin for which mETC is an "off target"

Headless Horseman: Adversarial Attacks on Transfer Learning Models

Transfer learning facilitates the training of task-specific classifiers using pre-trained models as feature extractors. We present a family of transferable adversarial attacks against such classifiers, generated without access to the classification head; we call these \emph{headless attacks}. We first demonstrate successful transfer attacks against a victim network using \textit{only} its feature extractor. This motivates the introduction of a label-blind adversarial attack. This transfer attack method does not require any information about the class-label space of the victim. Our attack lowers the accuracy of a ResNet18 trained on CIFAR10 by over 40\%.Comment: 5 pages, 2 figures. Accepted in ICASSP 2020. Code available on https://github.com/zhuchen03/headless-attack.gi

Earthworm invasion into previously earthworm-free temperate and boreal forests

Earthworms are keystone detritivores that can influence primary producers by changing seedbed conditions, soil characteristics, flow of water, nutrients and carbon, and plant–herbivore interactions. The invasion of European earthworms into previously earthworm-free temperate and boreal forests of North America dominated by Acer, Quercus, Betula, Pinus and Populus has provided ample opportunity to observe how earthworms engineer ecosystems. Impacts vary with soil parent material, land use history, and assemblage of invading earthworm species. Earthworms reduce the thickness of organic layers, increase the bulk density of soils and incorporate litter and humus materials into deeper horizons of the soil profile, thereby affecting the whole soil food web and the above ground plant community. Mixing of organic and mineral materials turns mor into mull humus which significantly changes the distribution and community composition of the soil microflora and seedbed conditions for vascular plants. In some forests earthworm invasion leads to reduced availability and increased leaching of N and P in soil horizons where most fine roots are concentrated. Earthworms can contribute to a forest decline syndrome, and forest herbs in the genera Aralia, Botrychium, Osmorhiza, Trillium, Uvularia, and Viola are reduced in abundance during earthworm invasion. The degree of plant recovery after invasion varies greatly among sites and depends on complex interactions with soil processes and herbivores. These changes are likely to alter competitive relationships among plant species, possibly facilitating invasion of exotic plant species such as Rhamnus cathartica into North American forests, leading to as yet unknown changes in successional trajectory

Exploring UK medical school differences: the MedDifs study of selection, teaching, student and F1 perceptions, postgraduate outcomes and fitness to practise.

BACKGROUND: Medical schools differ, particularly in their teaching, but it is unclear whether such differences matter, although influential claims are often made. The Medical School Differences (MedDifs) study brings together a wide range of measures of UK medical schools, including postgraduate performance, fitness to practise issues, specialty choice, preparedness, satisfaction, teaching styles, entry criteria and institutional factors. METHOD: Aggregated data were collected for 50 measures across 29 UK medical schools. Data include institutional history (e.g. rate of production of hospital and GP specialists in the past), curricular influences (e.g. PBL schools, spend per student, staff-student ratio), selection measures (e.g. entry grades), teaching and assessment (e.g. traditional vs PBL, specialty teaching, self-regulated learning), student satisfaction, Foundation selection scores, Foundation satisfaction, postgraduate examination performance and fitness to practise (postgraduate progression, GMC sanctions). Six specialties (General Practice, Psychiatry, Anaesthetics, Obstetrics and Gynaecology, Internal Medicine, Surgery) were examined in more detail. RESULTS: Medical school differences are stable across time (median alpha = 0.835). The 50 measures were highly correlated, 395 (32.2%) of 1225 correlations being significant with p < 0.05, and 201 (16.4%) reached a Tukey-adjusted criterion of p < 0.0025. Problem-based learning (PBL) schools differ on many measures, including lower performance on postgraduate assessments. While these are in part explained by lower entry grades, a surprising finding is that schools such as PBL schools which reported greater student satisfaction with feedback also showed lower performance at postgraduate examinations. More medical school teaching of psychiatry, surgery and anaesthetics did not result in more specialist trainees. Schools that taught more general practice did have more graduates entering GP training, but those graduates performed less well in MRCGP examinations, the negative correlation resulting from numbers of GP trainees and exam outcomes being affected both by non-traditional teaching and by greater historical production of GPs. Postgraduate exam outcomes were also higher in schools with more self-regulated learning, but lower in larger medical schools. A path model for 29 measures found a complex causal nexus, most measures causing or being caused by other measures. Postgraduate exam performance was influenced by earlier attainment, at entry to Foundation and entry to medical school (the so-called academic backbone), and by self-regulated learning. Foundation measures of satisfaction, including preparedness, had no subsequent influence on outcomes. Fitness to practise issues were more frequent in schools producing more male graduates and more GPs. CONCLUSIONS: Medical schools differ in large numbers of ways that are causally interconnected. Differences between schools in postgraduate examination performance, training problems and GMC sanctions have important implications for the quality of patient care and patient safety

The Analysis of Teaching of Medical Schools (AToMS) survey: an analysis of 47,258 timetabled teaching events in 25 UK medical schools relating to timing, duration, teaching formats, teaching content, and problem-based learning.

BACKGROUND: What subjects UK medical schools teach, what ways they teach subjects, and how much they teach those subjects is unclear. Whether teaching differences matter is a separate, important question. This study provides a detailed picture of timetabled undergraduate teaching activity at 25 UK medical schools, particularly in relation to problem-based learning (PBL). METHOD: The Analysis of Teaching of Medical Schools (AToMS) survey used detailed timetables provided by 25 schools with standard 5-year courses. Timetabled teaching events were coded in terms of course year, duration, teaching format, and teaching content. Ten schools used PBL. Teaching times from timetables were validated against two other studies that had assessed GP teaching and lecture, seminar, and tutorial times. RESULTS: A total of 47,258 timetabled teaching events in the academic year 2014/2015 were analysed, including SSCs (student-selected components) and elective studies. A typical UK medical student receives 3960 timetabled hours of teaching during their 5-year course. There was a clear difference between the initial 2 years which mostly contained basic medical science content and the later 3 years which mostly consisted of clinical teaching, although some clinical teaching occurs in the first 2 years. Medical schools differed in duration, format, and content of teaching. Two main factors underlay most of the variation between schools, Traditional vs PBL teaching and Structured vs Unstructured teaching. A curriculum map comparing medical schools was constructed using those factors. PBL schools differed on a number of measures, having more PBL teaching time, fewer lectures, more GP teaching, less surgery, less formal teaching of basic science, and more sessions with unspecified content. DISCUSSION: UK medical schools differ in both format and content of teaching. PBL and non-PBL schools clearly differ, albeit with substantial variation within groups, and overlap in the middle. The important question of whether differences in teaching matter in terms of outcomes is analysed in a companion study (MedDifs) which examines how teaching differences relate to university infrastructure, entry requirements, student perceptions, and outcomes in Foundation Programme and postgraduate training

Redox regulation of the calcium activated and voltage gated potassium channel, BK: shaping the pancreatic beta cells action potential and calcium influx

Large conductance calcium activated potassium channels (BK) are ubiquitous in the membranes of all excitable cells and are responsible for limiting action potential propagation and cell function by hyperpolarising action potentials, there is evidence that BK channels are important for the function of pancreatic β cells. Hydrogen peroxide (H2O2) is a reactive oxygen species commonly found in all cell types and known to have an effect on BK channels. In this study electrophysiology and fluorescence imaging were used determine the effect of hydrogen peroxide on BK channel activity and action potential shaping. In single-channel patches BK channels were activated by hydrogen peroxide with a bell-shaped relationship, 1 µM H2O2 was shown to be the most stimulatory concentration, identified by a 1000-fold increase in open channel probability (p = 0.0280). From whole-cell recordings, carried out to confirm activity across the whole cell and measure the voltage dependent effects, it was shown that this was a universal effect across the entire cell membrane with a 24% increase in potassium current amplitude (p = 0.0224), the effect of hydrogen peroxide acting on BK was confirmed by the blockers quinine and paxilline. Inside-out patch showed that hydrogen peroxide acted directly on channels to stimulate channel opening (p = 0.0141). Current-clamp recordings showed that hydrogen peroxide had no significant effect on the shape of action potentials in terms of baseline membrane potential, peak amplitude; half-width and maximum rate of decay of spiking, stimulated by 2.5 and 10 mM glucose. Through calcium imaging it was observed that H2O2 had no significant effect on calcium influx. It was concluded that although hydrogen peroxide directly activates BK channels in β cells, this effect is insufficient to alter the shape of glucose-stimulated action potentials or calcium influx

Experimental Models of Traumatic Injuries: Do They Capture the Coagulopathy and Underlying Endotheliopathy Induced by Human Trauma?

Peer reviewed: TrueTrauma-induced coagulopathy (TIC) is a major cause of morbidity and mortality in patients with traumatic injury. It describes the spectrum of coagulation abnormalities that occur because of the trauma itself and the body's response to the trauma. These coagulation abnormalities range from hypocoagulability and hyperfibrinolysis, resulting in potentially fatal bleeding, in the early stages of trauma to hypercoagulability, leading to widespread clot formation, in the later stages. Pathological changes in the vascular endothelium and its regulation of haemostasis, a phenomenon known as the endotheliopathy of trauma (EoT), are thought to underlie TIC. Our understanding of EoT and its contribution to TIC remains in its infancy largely due to the scarcity of experimental research. This review discusses the mechanisms employed by the vascular endothelium to regulate haemostasis and their dysregulation following traumatic injury before providing an overview of the available experimental in vitro and in vivo models of trauma and their applicability for the study of the EoT and its contribution to TIC