Peter Baker

Axonal Calcium and Magnesium Homeostasis

Publisher Summary The squid axon provides a key preparation for unraveling the complexities of cellular calcium (Ca) and magnesium (Mg) homeostasis. Chemical analysis of axoplasm shows it to contain 100 times as much Mg as Ca, the ratio of free Mg to free Ca is probably nearer 500,000: 1. Axoplasm and squid blood also contain measurable amounts of other divalent cations, including Sr, Mn, Zn, and Co. Despite the fact that each of these cations is strongly bound in axoplasm, in no case does the total axoplasmic concentration approach is expected for an ion distributed in accordance with the membrane potential. The presence of ATP and other cytoplasmic anions can account quantitatively for the bound fraction of axoplasmic Mg. The application of metabolic poisons brings about a small rise in ionized Mg roughly in parallel with the disappearance of ATP. Moreover, efflux of Mg is dependent on external Na and may reflect an exchange of intracellular Mg for external Na.

Clinical features of patients isolated for suspected Ebola virus disease at Connaught Hospital, Freetown, Sierra Leone: a retrospective cohort study

BACKGROUND The size of the west African Ebola virus disease outbreak led to the urgent establishment of Ebola holding unit facilities for isolation and diagnostic testing of patients with suspected Ebola virus disease. Following the onset of the outbreak in Sierra Leone, patients presenting to Connaught Hospital in Freetown were screened for suspected Ebola virus disease on arrival and, if necessary, were admitted to the on-site Ebola holding unit. Since demand for beds in this unit greatly exceeded capacity, we aimed to improve the selection of patients with suspected Ebola virus disease for admission by identifying presenting clinical characteristics that were predictive of a confirmed diagnosis. METHODS In this retrospective cohort study, we recorded the presenting clinical characteristics of suspected Ebola virus disease cases admitted to Connaught Hospitals Ebola holding unit. Patients were subsequently classified as confirmed Ebola virus disease cases or non-cases according to the result of Ebola virus reverse-transcriptase PCR (EBOV RT-PCR) testing. The sensitivity, specificity, positive predictive value, negative predictive value, and likelihood ratio of every clinical characteristic were calculated, to estimate the diagnostic accuracy and predictive value of each clinical characteristic for confirmed Ebola virus disease. RESULTS Between May 29, 2014, and Dec 8, 2014, 850 patients with suspected Ebola virus disease were admitted to the holding unit, of whom 724 had an EBOV RT-PCR result recorded and were included in the analysis. In 464 (64%) of these patients, a diagnosis of Ebola virus disease was confirmed. Fever or history of fever (n=599, 83%), intense fatigue or weakness (n=495, 68%), vomiting or nausea (n=365, 50%), and diarrhoea (n=294, 41%) were the most common presenting symptoms in suspected cases. Presentation with intense fatigue, confusion, conjunctivitis, hiccups, diarrhea, or vomiting was associated with increased likelihood of confirmed Ebola virus disease. Three or more of these symptoms in combination increased the probability of Ebola virus disease by 3·2-fold (95% CI 2·3-4·4), but the sensitivity of this strategy for Ebola virus disease diagnosis was low. In a subgroup analysis, 15 (9%) of 161 confirmed Ebola virus disease cases reported neither a history of fever nor a risk factor for Ebola virus disease exposure. INTERPRETATION Discrimination of Ebola virus disease cases from patients without the disease is a major challenge in an outbreak and needs rapid diagnostic testing. Suspected Ebola virus disease case definitions that rely on history of fever and risk factors for Ebola virus disease exposure do not have sufficient sensitivity to identify all cases of the disease. FUNDING None.

The Relation between Ionized Calcium and Cortical Granule Exocytosis in Eggs of the Sea Urchin Echinus esculentus

By subjecting sea urchin eggs to intense, short-duration, electric fields the permeability to low relative molecular mass substances is markedly increased. After such treatment, the extracellular space markers 22Na+ and [14C]mannitol penetrate into the interior of the egg and localized destruction of the oolemma is apparent. The technique permits the rapid introduction of low relative molecular mass substances into the interior of the egg. We have employed it to investigate the efficacy of various buffered calcium concentrations in bringing about exocytosis of cortical granules of the egg. Eggs rendered permeable in the presence of EGTA (free Ca < 10-8M) retain a full complement of cortical granules and appear little different in cortical ultrastructure from unfertilized eggs, as judged by scanning and transmission electron microscopy. The proportion of cortical granules remaining in the egg cortex 30 s after application of an electric field in the presence of higher concentrations of calcium decreases progressively as the free calcium concentration introduced into the egg interior is increased from 0.5 to 6 μM. The disappearance of the cortical granules is attributed to their having undergone exocytosis, since the changes in cortical ultrastructure that result from treatment with micro-molar calcium concentrations are demonstrated to be similar to the changes that result from exocytosis of the cortical granules in intact eggs after fertilization.

Control of intracellular pH in rat calvarial osteoblasts: Coexistence of both chloride-bicarbonate and sodium-hydrogen exchange

SummaryIntracellular pH was monitored continuously in cultured rat calvarial osteoblasts using the pH-sensitive fluorescent dye bis carboxyethyl carboxyfluorescein (BCECF), loaded into the cells as its membrane permeant ester. Recovery from an intracellular acid load generated by exposure to NH4Cl was unaffected by the anion exchange inhibitors 4-acetamido-4′-isothiocyanato-stilbene-2,2′-disuphonic acid (SITS) and 4,4′-diisothiocyanatostilbene 2,2′-disuphonic acid (DIDS) (100 μM), but blocked by the sodium-hydrogen exchange inhibitor amiloride (1 mM) and dependent on external sodium, suggesting that recovery is brought about by a sodium-hydrogen exchanger in the plasma membrane. The cells do, however, possess a SITS-sensitive chloride-bicarbonate exchanger, because iso-osmotic replacement of chloride by gluconate leads to intracellular alkalinization, that is inhibited by SITS, but independent of external sodium. Parathyroid hormone brings about an intracellular acidification, which may be due to an inhibition of sodium-hydrogen exchange.

Transport of Sugars and Amino Acids

Publisher Summary This chapter describes the properties of sugar and amino acid fluxes and their regulation in the giant axon of Loligo forbesi. The giant axon has transport systems for sugars and amino acids and they reveal many features in common with the mammalian brain. Sugar transport in the squid giant axon is regulated in a manner that serves to maintain axoplasmic sugar levels. Compared to other tissues, D-glucose is metabolized slowly by the giant axon. As such, under conditions where the metabolic requirements of the giant axon are increased, uptake of sugar is not rate-limiting for metabolism. In addition, amino acid transport has been categorized on the basis of amino acid type—acidic, basic, and neutral amino acid transport systems. An analysis of the various categories of amino acid transport is lacks in the squid axon. A systematic analysis of the characteristics of the transport of organic molecules into squid axons may reveal a number of processes of widespread interest.

Shortage of public health independence and advocacy in the UK

As public health registrars we believe it is the duty of UK public health institutions to advocate strongly for evidence-based measures to improve the health of society. However, several public health reports have made us concerned about the independence of our institutions. One example is the latest Chief Medical Officer’s report on child health. We were struck by the mismatch between the problems identified and the actions recommended. The report excellently highlights the social determinants of poor child health. However, its recommendations focus on healthcare services (such as giving out more vitamins) with no recommendations to tackle the social determinants of health (such as tackling child poverty). When the report cites the work of the WHO Commission on Social Determinants of Health, individual-level targets, such as parental education, are singled out, rather than wider recommendations such as social inclusion of caregivers, childcare, flexible working hours, or full and fair employment. A second example is the exclusion of climate change from the analysis of the health impacts of fracking by Public Health England. Such limited analyses give out harmful messages that can be easily misinterpreted. Our criticism is not aimed at any individuals, but at the institutional restrictions preventing bolder analysis of public health issues. We agree with Marmot and Kickbusch that a “health in all policies” approach is central to a healthy society. Public health must be free to draw attention to any potential eff ect on health of any government policies. So what is to be done? First, Public Health England and the Chief Medical Officer should be independent expert advisers, with no political interference in the scope or focus of their work. Only this will maintain their public credibility. Second, public health professionals must champion the “health in all policies” approach at every opportunity. Third, public health professionals should actively engage with policy makers, civil society, and the media to facilitate this. The increasing influence of tobacco, alcohol, and food industries on government policy show the increasing inability of the public health profession to work eff ectively. Shying away from advocacy is comparable to medical negligence. The changes taking place in UK public health present a unique opportunity for strong, independent public health institutions, and determined public health advocacy. This could bring tremendous gains to the health of our populations.

A pilot randomized controlled trial of sleep therapy in Parkinson's disease: effect on patients and caregivers

By means of a controlled trial, to investigate the efficacy, tolerability and feasibility of a multi‐component sleep therapy intervention versus basic sleep hygiene education in PD patients with sleep disturbances and their live‐in carers.

Quantifying the risk of nosocomial infection within Ebola Holding Units: a retrospective cohort study of negative patients discharged from five Ebola Holding Units in Western Area, Sierra Leone

A central pillar in the response to the 2014 Ebola virus disease (EVD) epidemic in Sierra Leone was the role of Ebola Holding Units (EHUs). These units isolated patients meeting a suspect case definition, tested them for EVD, initiated appropriate early treatment and discharged negative patients to onward inpatient care or home. Positive patients were referred to Ebola Treatment Centres. We aimed to estimate the risk of nosocomial transmission within these EHUs.

Chapter 4 Exocytosis in Electropermeabilized Cells: Clues to Mechanism and Physiological Control

Publisher Summary Exocytosis is normally monitored by the appearance in the extracellular fluid of some secretory product; but this does not necessarily provide much information about the underlying fusion process as there may be a delay between the fusion and escape of secretory product. It is usual to divide exocytosis into two types—continuous and triggered—both of which are probably present to some extent in most cells. Continuous exocytosis provides for the steady turnover of membrane components and the apparently nonregulated release into the external fluid of proteins, such as albumin, immunoglobulins, and extracellular matrix components. Triggered exocytosis permits sudden changes, either in membrane composition—such as when antidiuretic hormone acts to increase the water transporting capacity of the distal nephron—or in the release of biologically active molecules, including nervous transmitter substances, many hormones, and enzymes. Permeabilization can be achieved by a variety of techniques of which two, electropermeabilization and detergent permeabilization, have been widely used. In suitable preparations, the cell membrane can also be permeabilied by exposure to certain toxins, viruses, complement, or ATP 4− . Permeabilized cells have permitted some features of exocytosis to be elucidated under conditions where the normal physiological controls have been by passed. Only a limited number of secretory systems have been investigated, but there are some common features: (1) exocytosis is activated in the micromolar range of calcium concentrations, (2) it is largely unaffected by a wide variety of agents that interact specifically with the cytoskeleton, (3) it can usually be inhibited by agents that also inhibit both calmodulin-dependent processes and protein kinase C, and (4) it is usually inhibited by raising the osmotic pressure of the medium by addition of sucrose.

Hormone-Sensitive Cyclic Nucleotide Metabolism in Giant Axons of Loligo

Publisher Summary This chapter examines cyclic nucleotide metabolism in giant axons of Loligo forbesi . Experiments suggest that the perfused squid axon may prove to be an excellent preparation to study the hormonal control of cAMP metabolism. It is of particular interest to extend these observations to cGMP, the level of which seems to be decreased by 5-HT, and to investigate the effects of membrane potential on cyclic nucleotide metabolism in perfused axons. The chapter also examines the action of 5-HT. It shows the relation between 5-HT concentration and cAMP levels in axoplasm. The increase in cAMP content is half-maximal at a 5-HT concentration of approximately 1 μM. This observation, together with the finding that the effect of 5-HT is abolished by inclusion in the external medium of the 5-HT antagonist methysergide, suggests that the squid axon contains conventional 5-HT receptors. A further question that must be addressed concerns the function of hormone-sensitive cyclic nucleotide metabolism in squid axons.