Mathematical modeling of intracellular osmolarity and cell volume stabilization: The Donnan effect and ion transport.

The presence of impermeant molecules within a cell can lead to an increase in cell volume through the influx of water driven by osmosis. This phenomenon is known as the Donnan (or Gibbs-Donnan) effect. Animal cells actively transport ions to counteract the Donnan effect and regulate their volume, actively pumping Na+ out and K+ into their cytosol using the Na+/K+ ATPase (NKA) pump. The pump-leak equations (PLEs) are a system of algebraic-differential equations to model the membrane potential, ion (Na+, K+, and Cl-), and water flux across the cell membrane, which provide insight into how the combination of passive ions fluxes and active transport contribute to stabilizing cell volume. Our broad objective is to provide analytical insight into the PLEs through three lines of investigation: (1) we show that the provision of impermeant extracellular molecules can stabilize the volume of a passive cell; (2) we demonstrate that the mathematical form of the NKA pump is not as important as the stoichiometry for cell stabilization; and (3) we investigate the interaction between the NKA pump and cation-chloride co-transporters (CCCs) on cell stabilization, showing that NCC can destabilize a cell while NKCC and KCC can stabilize it. We incorporate extracellular impermeant molecules, NKA pump, and CCCs into the PLEs and derive the exact formula for the steady states in terms of all the parameters. This analytical expression enables us to easily explore the effect of each of the system parameters on the existence and stability of the steady states.

Climate change and pavement burns in the United Kingdom: a case report of two patients.

Pavement burns are more common in locations familiarised with high temperatures and a dry climate zone, but have not previously been reported in temperate climates. We present two cases of patients who suffered pavement burns in the United Kingdom during an unprecedentedly hot day in July 2022. The first case involved a 66-year-old male who suffered partial and full thickness burns requiring excision and skin grafting. The second case involved a 58-year-old female with partial thickness burns also requiring excision and skin grafting. Both patients had pre-existing co-morbidities and their pavement burns were precipitated by heat stroke. Pavement burns represent a mechanism of injury that necessitates increased operative management, length of hospital stay and cost per surface area burned when compared to flame or scald burns (Silver et al., 2015). As a result of global warming, we anticipate extreme heat events, and subsequently pavement burns, to increase in incidence in the United Kingdom. There is opportunity for education of the public and health professionals for prevention.

The physical basis of osmosis.

Osmosis is an important force in all living organisms, yet the molecular basis of osmosis is widely misunderstood as arising from diffusion of water across a membrane separating solutions of differing osmolarities, and hence different water concentrations. In 1923, Peter Debye proposed a physical model for a semipermeable membrane emphasizing the repulsive forces between solute molecules and membrane that prevent the solute from entering the membrane. His work was hardly noticed at the time and slipped out of view. We show that Debye's analysis of van 't Hoff's law for osmotic equilibrium also provides a consistent and plausible mechanism for osmotic flow. A difference in osmolyte concentrations in solutions separated by a semipermeable membrane leads to different pressures at the two water-membrane interfaces because the total repulsive force between solute molecules and the membrane is different at the two interfaces. Water is therefore driven through the membrane for exactly the same reason that pure water flows in response to an imposed hydrostatic pressure difference. In this paper, we present the Debye model in both equilibrium and flow conditions. We point out its applicability regardless of the nature of the membrane with examples ranging from the predominantly convective flow of water through synthetic membranes and capillary walls to the purely diffusive flow of independent water molecules through a lipid bilayer and the flow of a single-file column of water molecules in narrow protein channels.

A sensitive and specific genetically-encoded potassium ion biosensor for in vivo applications across the tree of life.

Potassium ion (K+) plays a critical role as an essential electrolyte in all biological systems. Genetically-encoded fluorescent K+ biosensors are promising tools to further improve our understanding of K+-dependent processes under normal and pathological conditions. Here, we report the crystal structure of a previously reported genetically-encoded fluorescent K+ biosensor, GINKO1, in the K+-bound state. Using structure-guided optimization and directed evolution, we have engineered an improved K+ biosensor, designated GINKO2, with higher sensitivity and specificity. We have demonstrated the utility of GINKO2 for in vivo detection and imaging of K+ dynamics in multiple model organisms, including bacteria, plants, and mice.

Myogenic contraction of a somatic muscle powers rhythmic flow of hemolymph through Drosophila antennae and generates brain pulsations.

Hemolymph is driven through the antennae of Drosophila melanogaster by the rhythmic contraction of muscle 16 (m16), which runs through the brain. Contraction of m16 results in the expansion of an elastic ampulla, opening ostia and filling the ampulla. Relaxation of the ampullary membrane forces hemolymph through vessels into the antennae. We show that m16 is an auto-active rhythmic somatic muscle. The activity of m16 leads to the rapid perfusion of the antenna by hemolymph. In addition, it leads to the rhythmic agitation of the brain, which could be important for clearing the interstitial space.

Management of minor burns during the COVID-19 pandemic: A patient-centred approach.

INTRODUCTION: The UK government introduced lockdown measures on 23 March 2020 due to the first wave of the COVID-19 pandemic. A restructuring of clinical services was necessary to accommodate mandatory changes while also maintaining the best possible standards for patient care. The present study explored the initial management, follow-up and patient-reported outcomes of burn injuries <15% total body surface area (TBSA) during the height of the COVID-19 lockdown at a tertiary burns centre. METHODS: A retrospective review of all adult patients with burns <15% TBSA during the national lockdown (23 March 2020 to 10 May 2020) was undertaken at The Queen Elizabeth Hospital Birmingham (QEHB), UK. All referrals from non-QEHB telemedicine (external) or QEHB emergency (internal) departments were reviewed for management, length of hospital stay and pattern of follow-up (ward attender, self-care, community or outreach nurses). A telephone survey based on a structured questionnaire was conducted to establish patients' satisfaction. RESULTS: A total of 84 burn patients were included in the study. The mean age was 39 years (age range = 19-91 years) and the male:female ratio was 4:1. Patients were managed non-operatively (n = 69, 82%) or operatively (n = 15, 18%). Patients attended the ward attender acute burns clinic only once (n = 36, 61%). The telephone survey captured 70% (n = 59) of the study population and 57 patients (97% of respondents) were pleased with the ongoing care and burn healing. CONCLUSION: The integration of patient led self-care, reduction in admissions, minimal clinics attendance and a telemedicine follow-up is an effective model for small burns management during the COVID-19 pandemic. A high degree of patient satisfaction was achieved with continuous and approachable communication channels with the burn multidisciplinary team. We continue to implement this effective model of burns management throughout the COVID-19 pandemic and the subsequent period. LAY SUMMARY: The lockdown measures due to the first wave of COVID-19 pandemic affected the way we manage all medical emergencies including burns. The initial management, follow-up and patient satisfaction for small burn injuries during lockdown has not been reported previously. The aim of this study is to examine the outcome in terms of small burn management, hospital stay, number of clinic reviews, healing and patient satisfaction during the lockdown period in a burn centre in the UK. This would look at the need for operations and whether patients stayed longer if they required an intervention. We reviewed adult patients with small burns during the national lockdown (23 March 2020 to 10 May 2020) at The Queen Elizabeth Hospital Birmingham (QEHB). All referrals from telemedicine, referral system (external) or QEHB (internal) were reviewed for management, length of hospital stay and pattern of follow-up. Patients were reviewed in the acute burns clinic and given advice for burn management and dressing for self-care. Follow-up was mostly via email (telemedicine) A telephone survey based on a structured questionnaire was conducted to find out patients' satisfaction. Four times more men than women had small burns during the lockdown period. The average age was 39 years. The majority were managed conservatively with dressings (82%) and a small proportion required an operation (18%). Most patients attended the acute burns clinic only once (61%) for initial assessment and management. The telephone survey captured 70% of patient and 97% of respondents were pleased with the care and burn healing. The integration of patient-led self-care, reduction in admissions, minimal clinics attendance and a telemedicine follow-up is an effective model for burns management during the COVID-19 pandemic. A high degree of patient satisfaction was achieved with continuous and approachable communication channels with burn multidisciplinary team. We continue to implement this effective model of burns management throughout the COVID-19 pandemic and the subsequent period.

Improving Management of Limb Injuries in Disasters and Conflicts.

It has become clear that disaster relief needs to transition from good intentions or a charity-based approach to a professional, outcome-oriented response. The practice of medicine in disaster and conflict is a profession practiced in environments where lack of resources, chaos, and unpredictability are the norm rather than the exception. With this consideration in mind, the World Health Organization (WHO; Geneva, Switzerland) and its partners set out to improve the disaster response systems. The resulting Emergency Medical Team (EMT) classification system requires that teams planning on engaging in disaster response follow common standards for the delivery of care in resource-constraint environments. In order to clarify these standards, the WHO EMT Secretariat collaborated with the International Committee of the Red Cross (ICRC; Geneva, Switzerland) and leading experts from other stakeholder non-governmental organizations (NGOs) to produce a guide to the management of limb injuries in disaster and conflict.The resulting text is a free and open-access resource to provide guidance for national and international EMTs caring for patients in disasters and conflicts. The content is a result of expert consensus, literature review, and an iterative process designed to encourage debate and resolution of existing open questions within the field of disaster and conflict medical response.The end result of this process is a text providing guidance to providers seeking to deliver safe, effective care within the EMT framework that is now part of the EMT training and verification system and is being distributed to ICRC teams deploying to the field.This work seeks to encourage professionalization of the field of disaster and conflict response, and to contribute to the existing EMT framework, in order to provide for better care for future victims of disaster and conflict.Jensen G, Bar-On E, Wiedler JT, Hautz SC, Veen H, Kay AR, Norton I, Gosselin RA, von Schreeb J. Improving management of limb injuries in disasters and conflicts. Prehosp Disaster Med. 2019;34(3):330-334.

Evolution of our understanding of cell volume regulation by the pump-leak mechanism.

All animal cells are surrounded by a flexible plasma membrane that is permeable to water and to small ions. Cells thus face a fundamental problem: the considerable tension that their membranes would experience if the osmotic influx of water, driven by the presence of impermeant intracellular ions, was left unopposed. The pivotal study that described the cell's remedy for this impending osmotic catastrophe-the "pump-leak mechanism" (PLM)-was published in the Journal of General Physiology by Tosteson and Hoffman in 1960. Their work revealed how the sodium pump stabilizes cell volume by eliminating the osmotic gradient. Here we describe the mechanistic basis of the PLM, trace the history of its discovery, and place it into the context of our current understanding.

Non-F HBV/HDV-3 coinfection is associated with severe liver disease in Western Brazilian Amazon.

The clinical outcome of hepatitis B virus (HBV) infection may be related to host and viral genetic factors, as well as to the type of infection (monoinfection and coinfection). To analyze the distribution/combination of HBV/hepatitis D virus (HDV) genotypes and the associated clinical characteristics, 409 serum samples from patients with chronic HBV (94 of them coinfected by HDV) followed at the Viral Hepatitis Referral Center of Rio Branco, Brazil were enrolled. HBV DNA and HDV RNA were amplified, respectively, by polymerase chain reaction (PCR) and nested PCR using specific primers in the PreC/C region and the S gene, and by reverse-transcription PCR and seminested PCR using specific primers in the delta antigen region and sequenced. The proportion of women (56.1%) was significantly higher than males in this cohort ( P < 0.01). Women were significantly younger (39.8 years; 8-77 years) than males (44.7 years; 12-79 years; P < 0.01). Sixty-eight (18%) patients were infected with HBV-F genotype and 264 (69.8%) with HBV/non-F genotypes. Coinfection by HDV was detected in 23.9% (94 of 409) of this population and was more frequent in male (54.2%, 51 of 94) than in female patients (44.7%, 42 of 94; P = 0.015). HDV-3 was the most prevalent (88.9%) genotype. Almost 70% of HDV-3 coinfected patients were infected with HBV/non-F genotypes. Severe liver disease was diagnosed in 41 patients, 60.9% (25 of 41) of them coinfected with HDV. HBV/HDV coinfection was associated with male sex, age above 30 years, severe liver disease, and increased alanine aminotransferase levels. HBV/HDV-3 coinfection is associated with severe liver disease, in Rio Branco, Brazil.

Biophysical models reveal the relative importance of transporter proteins and impermeant anions in chloride homeostasis.

Fast synaptic inhibition in the nervous system depends on the transmembrane flux of Cl- ions based on the neuronal Cl- driving force. Established theories regarding the determinants of Cl- driving force have recently been questioned. Here, we present biophysical models of Cl- homeostasis using the pump-leak model. Using numerical and novel analytic solutions, we demonstrate that the Na+/K+-ATPase, ion conductances, impermeant anions, electrodiffusion, water fluxes and cation-chloride cotransporters (CCCs) play roles in setting the Cl- driving force. Our models, together with experimental validation, show that while impermeant anions can contribute to setting [Cl-]i in neurons, they have a negligible effect on the driving force for Cl- locally and cell-wide. In contrast, we demonstrate that CCCs are well-suited for modulating Cl- driving force and hence inhibitory signaling in neurons. Our findings reconcile recent experimental findings and provide a framework for understanding the interplay of different chloride regulatory processes in neurons.

Hepatitis B and hepatitis D virus infections in the Central African Republic, twenty-five years after a fulminant hepatitis outbreak, indicate continuing spread in asymptomatic young adults.

Hepatitis delta virus (HDV) increases morbidity in Hepatitis B virus (HBV)-infected patients. In the mid-eighties, an outbreak of HDV fulminant hepatitis (FH) in the Central African Republic (CAR) killed 88% of patients hospitalized in Bangui. We evaluated infections with HBV and HDV among students and pregnant women, 25 years after the fulminant hepatitis (FH) outbreak to determine (i) the prevalence of HBV and HDV infection in this population, (ii) the clinical risk factors for HBV and/or HDV infections, and (iii) to characterize and compare the strains from the FH outbreak in the 1980s to the 2010 HBV-HDV strains. We performed a cross sectional study with historical comparison on FH-stored samples (n = 179) from 159 patients and dried blood-spots from volunteer students and pregnant women groups (n = 2172). We analyzed risk factors potentially associated with HBV and HDV. Previous HBV infection (presence of anti-HBc) occurred in 345/1290 students (26.7%) and 186/870 pregnant women (21.4%)(p = 0.005), including 110 students (8.8%) and 71 pregnant women (8.2%), who were also HBsAg-positive (p = 0.824). HDV infection occurred more frequently in pregnant women (n = 13; 18.8%) than students (n = 6; 5.4%) (p = 0.010). Infection in childhood was probably the main HBV risk factor. The risk factors for HDV infection were age (p = 0.040), transfusion (p = 0.039), and a tendency for tattooing (p = 0.055) and absence of condom use (p = 0.049). HBV-E and HDV-1 were highly prevalent during both the FH outbreak and the 2010 screening project. For historical samples, due to storage conditions and despite several attempts, we could only obtain partial HDV amplification representing 25% of the full-length genome. The HDV-1 mid-eighties FH-strains did not form a specific clade and were affiliated to two different HDV-1 African subgenotypes, one of which also includes the 2010 HDV-1 strains. In the Central African Republic, these findings indicate a high prevalence of previous and current HBV-E and HDV-1 infections both in the mid-eighties fulminant hepatitis outbreak and among asymptomatic young adults in 2010, and reinforce the need for universal HBV vaccination and the prevention of HDV transmission among HBsAg-positive patients through blood or sexual routes.

Conceptualizing the health and well-being impacts of social enterprise: a UK-based study.

Social enterprises-businesses that work for social benefit rather than for the maximization of financial returns to shareholders or owners-could potentially prove to be an innovative and sustainable way of tackling 'upstream' social determinants of health. However, empirical work focusing upon how, and to what extent, social enterprise-led activity may impact upon health and well-being is still relatively scarce. This study examines how social enterprises portray their impact, and how such impacts may be considered in health and well-being terms. Through analysing evaluative reports of the work of social enterprises in Scotland (n = 17) utilizing a 'process coding' method, we investigate both the self-reported impacts of the work of social enterprises and the mechanisms by which these are said to be derived. Revisiting previous conceptualizations in the extant literature, this work allows us to present an 'empirically-informed' conceptual model of the health and well-being impacts of social enterprise-led activity, and thus presents a significant advance on previous hypothetical, theoretically-based conceptualizations. It is considered that these findings further improve our overall knowledge of ways in which social enterprise and other parts of the third sector could be considered as potentially valuable 'non-obvious' public health actors.

How Cells Can Control Their Size by Pumping Ions.

The ability of all cells to set and regulate their size is a fundamental aspect of cellular physiology. It has been known for sometime but not widely so, that size stability in animal cells is dependent upon the operation of the sodium pump, through the so-called pump-leak mechanism (Tosteson and Hoffman, 1960). Impermeant molecules in cells establish an unstable osmotic condition, the Donnan effect, which is counteracted by the operation of the sodium pump, creating an asymmetry in the distribution of Na+ and K+ staving off water inundation. In this paper, which is in part a tutorial, I show how to model quantitatively the ion and water fluxes in a cell that determine the cell volume and membrane potential. The movement of water and ions is constrained by both osmotic and charge balance, and is driven by ion and voltage gradients and active ion transport. Transforming these constraints and forces into a set of coupled differential equations allows us to model how the ion distributions, volume and voltage change with time. I introduce an analytical solution to these equations that clarifies the influence of ion conductances, pump rates and water permeability in this multidimensional system. I show that the number of impermeant ions (x) and their average charge have a powerful influence on the distribution of ions and voltage in a cell. Moreover, I demonstrate that in a cell where the operation of active ion transport eliminates an osmotic gradient, the size of the cell is directly proportional to x. In addition, I use graphics to reveal how the physico-chemical constraints and chemical forces interact with one another in apportioning ions inside the cell. The form of model used here is applicable to all membrane systems, including mitochondria and bacteria, and I show how pumps other than the sodium pump can be used to stabilize cells. Cell biologists may think of electrophysiology as the exclusive domain of neuroscience, however the electrical effects of ion fluxes need to become an intimate part of cell biology if we are to understand a fundamental process like cell size regulation.

Goggatomy: A Method for Opening Small Cuticular Compartments in Arthropods for Physiological Experiments.

Most sense organs of arthropods are ensconced in small exoskeletal compartments that hinder direct access to plasma membranes. We have developed a method for exposing live sensory and supporting cells in such structures. The technique uses a viscous light cured resin to embed and support the structure, which is then sliced with a sharp blade. We term the procedure a "goggatomy," from the Khoisan word for a bug, gogga. To demonstrate the utility of the method we show that it can be used to expose the auditory chordotonal organs in the second antennal segment and the olfactory receptor neurons in the third antennal segment of Drosophila melanogaster, preserving the transduction machinery. The procedure can also be used on other small arthropods, like mosquitoes and mites to expose a variety of cells.

The Role of Military Plastic Surgeons in the Management of Modern Combat Trauma: An Analysis of 645 Cases.

BACKGROUND: Plastic surgery has historically been linked to war. Between 2008 and the end of combat operations in Afghanistan in 2014, British military plastic surgeons formed part of the multinational military surgical team at the Role 3 Medical Treatment Facility, Camp Bastion, Helmand Province. The present study aimed to analyze the activity of these surgeons objectively and to determine the utility of their deployment. METHODS: Data were gathered prospectively from four periods (2009 to 2012). This coincided with different surgeons, types of combat activity, wounding patterns, and mission emphases for the hospital. Various metrics were employed. RESULTS: Plastic surgeons were involved in 40 percent of surgical cases (645 of 1654). This was consistent, despite changes in the predominant wounding mechanism and casualty population. One-third of cases involved the plastic surgeon as the lead or sole surgeon and two-thirds involved working with surgeons from other disciplines. Caseload by anatomical region was as follows: hand and upper limb, 64 percent; head and neck, 46 percent; lower limb, 40 percent; and trunk, 25 percent. A median of 1.75 body areas were operated on per patient. Involvement did not differ between patients wearing combat body armor when injured and those who were not. CONCLUSIONS: Plastic surgeons played a significant role in the management of modern military trauma. This reflects the types of injuries sustained and the expertise of military plastic surgeons complementing the skill set of the other surgical team members. The level of activity was independent of wounding patterns, suggesting that the specialty may be useful, irrespective of the nature of the conflict.

Protein-peptide arrays for detection of specific anti-hepatitis D virus (HDV) genotype 1, 6, and 8 antibodies among HDV-infected patients by surface plasmon resonance imaging.

Liver diseases linked to hepatitis B-hepatitis D virus co- or superinfections are more severe than those during hepatitis B virus (HBV) monoinfection. The diagnosis of hepatitis D virus (HDV) infection therefore remains crucial in monitoring patients but is often overlooked. To integrate HDV markers into high-throughput viral hepatitis diagnostics, we studied the binding of anti-HDV antibodies (Abs) using surface plasmon resonance imaging (SPRi). We focused on the ubiquitous HDV genotype 1 (HDV1) and the more uncommon African-HDV6 and HDV8 genotypes to define an array with recombinant proteins or peptides. Full-length and truncated small hepatitis D antigen (S-HDAg) recombinant proteins of HDV genotype 1 (HDV1) and 11 HDV peptides of HDV1, 6, and 8, representing various portions of the delta antigen were grafted onto biochips, allowing SPRi measurements to be made. Sixteen to 17 serum samples from patients infected with different HDV genotypes were injected onto protein and peptide chips. In all, Abs against HDV proteins and/or peptides were detected in 16 out of 17 infected patients (94.12%), although the amplitude of the SPR signal varied. The amino-terminal part of the protein was poorly immunogenic, while epitope 65-80, exposed on the viral ribonucleoprotein, may be immunodominant, as 9 patient samples led to a specific SPR signal on peptide 65 type 1 (65#1), independently of the infecting genotype. In this pilot study, we confirmed that HDV infection screening based on the reactivity of patient Abs against carefully chosen HDV peptides and/or proteins can be included in a syndrome-based viral hepatitis diagnostic assay. The preliminary results indicated that SPRi studying direct physical HDAg-anti-HDV Ab interactions was more convenient using linear peptide epitopes than full-length S-HDAg proteins, due to the regeneration process, and may represent an innovative approach for a hepatitis syndrome-viral etiology-exploring array.

Improved rolling circle amplification (RCA) of hepatitis B virus (HBV) relaxed-circular serum DNA (RC-DNA).

For functional analysis of HBV isolates, epidemiological studies and correct identification of recombinant genomes, the amplification of complete genomes is necessary. A method for completely in vitro amplification of full-length HBV genomes starting from serum RC-DNA is described. This uses in vitro completion/ligation of plus-strand HBV RC-DNA and amplification using Rolling-Circle Amplification, eventually followed by a genomic PCR. The method can amplify complete HBV genomes from sera with viral loads ranging from >1.0E+8 IU/ml down to 1.0E+3 IU/ml. The method can be applied to archived sera that have undergone long-term storage or to archived DNA serum extracts. The genomes can easily be cloned. HBV genotypes A-G can all be amplified with no apparent problems. A recombinant subgenotype A3/genotype E genome was identified and fully sequenced.

HBVdb: a knowledge database for Hepatitis B Virus.

We have developed a specialized database, HBVdb (http://hbvdb.ibcp.fr), allowing the researchers to investigate the genetic variability of Hepatitis B Virus (HBV) and viral resistance to treatment. HBV is a major health problem worldwide with more than 350 million individuals being chronically infected. HBV is an enveloped DNA virus that replicates by reverse transcription of an RNA intermediate. HBV genome is optimized, being circular and encoding four overlapping reading frames. Indeed, each nucleotide of the genome takes part in the coding of at least one protein. However, HBV shows some genome variability leading to at least eight different genotypes and recombinant forms. The main drugs used to treat infected patients are nucleos(t)ides analogs (reverse transcriptase inhibitors). Unfortunately, HBV mutants resistant to these drugs may be selected and be responsible for treatment failure. HBVdb contains a collection of computer-annotated sequences based on manually annotated reference genomes. The database can be accessed through a web interface that allows static and dynamic queries and offers integrated generic sequence analysis tools and specialized analysis tools (e.g. annotation, genotyping, drug resistance profiling).