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Biomedical subjects

M C Evans

Publications and source records attributed to M C Evans.

At least 109 records · Page 6Linked to original sources
PubMed1982

Intracellular sites of early calcium accumulation in the rat hippocampus during status epilepticus.

Using electron microscopy and the combined oxalate--pyroantimonate technique, calcium was located in hippocampal neurons of rats that had undergone L-allylglycine-induced status epilepticus. In control material, calcium deposits were prominent in nearly every synaptic vesicle, and to a lesser degree in mitochondria and the Golgi apparatus of pyramidal neurons and dentate granule cells. After status epilepticus, mitochondrial calcium deposits increased, particularly in the swollen mitochondria of the pyramidal cell bodies and basal dendrites of CA3 and CA1 neurones. These studies support the theory that enhanced calcium entry leading to calcium overload of mitochondria may be an important cytotoxic mechanism producing selective neuronal loss.

Allylglycine↗
PubMed1982

Acute effects of sodium valproate and gamma-vinyl GABA on regional amino acid metabolism in the rat brain: incorporation of 2-[14C]glucose into amino acids.

Amino acid concentrations have been determined in rat brain regions (cortex, striatum, cerebellum, and hippocampus) by HPLC after administration of acute anticonvulsant doses of sodium valproate (400 mg/kg, i.p.) and gamma-vinyl-GABA (1 g/kg, i.p.). After valproate administration the GABA level increases only in the cortex; aspartic acid concentration decreases in the cortex and hippocampus, and glutamic acid decreases in the hippocampus and striatum and increases in the cortex and cerebellum. There are no changes in the concentrations of glutamine, taurine, glycine, serine, and alanine following valproate administration. Only the GABA level increases in all the regions after gamma-vinyl-GABA administration. Cortical analyses 2, 4 and 10 minutes after pulse labeling with 2-[14C]glucose, i.v., show no change in the rate of cortical glucose utilization in the valproate treated group. The rate of labeling of glutamic acid is also unchanged, but the rate of labeling of GABA is reduced following valproate administration. After gamma-vinyl-GABA administration there is no change in the rate of labeling of GABA. These biochemical findings can be interpreted in terms of a primary anticonvulsant action of valproate on membrane receptors with secondary effects on the metabolism of amino acid neurotransmitters. This contrasts with the primary action of gamma-vinyl-GABA on GABA-transaminase activity.

Amino Acids↗
PubMed1982

New dimensions in cause of death statistics.

This article discusses the limitations of traditional national cause of death statistics. These limitations derive from an attempt to conceptualize a multidimensional phenomenon and reduce down to a unidimensional framework. The article outlines the characteristics of a new multidimensional approach which involves the codification and tabulation of all causes (multiple causes) listed on death certificates. Preliminary data are presented which illustrate that multiple cause of death data do indeed represent a major new dimension to cause of death statistics. These data indicate that most major causes of death are contributory factors in many deaths in which they are not the underlying cause of death. For example, in 1976, diabetes mellitus was the underlying cause of approximately 35,000 deaths but was a contributing factor in another 100,000 deaths. This paper also demonstrates the contribution of multiple cause of death data to identifying patterns of association among diseases and the kinds of injuries resulting from various external causes. Finally, data are presented which depict the use of multiple cause data in evaluating the efficacy of the coding rules used to classify the underlying cause of death.

Computers↗
PubMed1981

EPR characteristics of oxygen-evolving photosytem II particles from Phormidium laminosum.

The EPR characteristics of oxygen evolving particles prepared from Phormidium laminosum are described. These particles are enriched in Photosystem II allowing EPR investigation of signals which were previously small or masked by those from Photosystem I in other preparations. EPR signals from a Signal II species and high potential cytochrome beta-559 appear as they are photooxidised at cryogenic temperatures by Photosystem II. The Signal II species is a donor close to the Photosystem II reaction centre and may represent part of the charge accumulation system of water oxidation. An EPR signal from an iron-sulphur centre which may represent an unidentified component of photosynthetic electron transport is also described. The properties of the oxygen evolving particles show that the preparation is superior to chloroplasts or unfractionated alga membranes for the study of Photosystem II with a functional water oxidation system.

Cell Membrane↗
PubMed1981

Comparison of the EPR properties of photosystem I iron-sulphur centres A and B in spinach and barley.

The properties of Photosystem I iron-sulphur centres A and B from spinach and barley chloroplasts were investigated by electron paramagnetic resonance spectroscopy (EPR). Barley chloroplasts were shown to photoreduce significant amounts of centre B at cryogenic temperatures unlike those from spinach which only photoreduced centre A. Centre B in barley chloroplasts was also reduced by dithionite before centre A and the EPR spectrum of reduced centre B was obtained. Illumination of barley chloroplasts at 15 K where centre B was chemically reduced resulted in the reduction of centre A and the appearance of spectral features indicating interaction between the two reduced centres. The variation of behaviours of iron-sulphur centres A and B between species favours a scheme of electron flow for Photosystem I where either centre A or centre B act as parallel electron acceptors from the earlier acceptor X.

Electron Spin Resonance Spectroscopy↗
PubMed1981

Mössbauer spectroscopic studies of the nature of centre X of photosystem I reaction centres from the cyanobacterium Chlorogloea fritschii.

Reduced photosystem I samples, which give the electron paramagnetic resonance (EPR) signals associated with A, A and B, and A, B and X centres, have been studied using Mössbauer spectroscopy. The Mössbauer spectra obtained from each type of sample is different, which indicates that iron is associated with all three centres. The spectra are similar to those obtained from ferredoxins with 4Fe-4S centres and were fitted with oxidized and reduced components, the relative proportions depending on the degree of reduction of the sample as monitored by EPR. The sample which gave only the A EPR signal showed about 26% of the reduced component, the sample which gave A and B EPR signals showed about 48% of the reduced component, while the sample which gave A, B and X EPR signals showed about 65% of the reduced component. The measurements are consistent with X being a 4Fe-S4 centre.

Cyanobacteria↗
PubMed1981

Growth hormone-like material in normal human tissues.

We report herein the presence of extractable levels of immunoassayable (RIA) and receptor-assayable human GH (hGH)-like material in normal human liver, kidney, lung, striated muscle, colon, stomach, and brain. Levels of hGH by RIA were the highest in the liver (mean, 14.7 ng/g), followed by those in the kidney (mean, 11.3 ng/g) and lung (mean, 4.6 ng/g), but small amounts were detected in at least some specimens of all types of tissue. This material eluted in the region of monomeric pituitary hGH on Sephadex G-100 chromatography and showed parallelism in a RIA to pituitary hGH on log-logit plots of dose-response lines. Passage of the material through an anti-hGH immunocolumn greatly reduced its immunoreactivity. Assay of eight sets of extracts by receptor assay using a male rat liver membrane preparation showed the GH-like substance to have a receptor to immunoassay potency ratio of 3.8:1 relative to monomeric hGH standard. Scrupulous correction for acidity, osmolality, and possible protein and enzyme effects and extraction of the hGH-like material by immunoabsorption excluded the possibility of artifacts causing the appearance of hGH-like material in the extracts.

Animals↗
PubMed1980

Coexisting Paget's disease of bone and hyperparathyroidism.

A patient with Paget's disease of bone and primary hyperparathyroidism is described. It has been suggested that a metabolite from pagetic tissue might stimulate parathyroid cell function. To test this, serum parathyroid hormone (iPTH) levels were measured by radio immunometric assay in 106 patients with Paget's disease of bone and 139 control subjects. There was no significant difference between the mean levels of the two groups. Of five sera with elevated PTH levels QUOSO extraction revealed an interfering substance in 3/5 from control patients tested and extractable iPTH in 2/2 from Paget's patients. One of the latter had renal failure. The results suggest that increased parathyroid function is unlikely to be a primary event in the genesis of Paget's disease of bone.

Aged↗
PubMed1979

Mössbauer spectra of photosystem-I-reaction centres from the blue-green alga Chlorogloea fritschii.

Substantial amounts of iron have been shown by Mössbauer spectroscopy to be present in Photosystem-I preparations from the blue-green alga Chlorogloeta fritschii. Changes in the spectra on chemical reduction provide evidence that some of this iron is very similar to that found in the 4Fe-4S centres of ferredoxins. Such reduced samples also show e.p.r. signals consistent with maximum reduction of iron-sulphur centres A and B of Photosystem I. An unchanged component in the spectra indicates, assuming all centres A and B are reduced, the presence of another iron-containing species.

Cell Membrane↗
PubMed1979

Electron-paramagnetic-resonance measurements of the electron-transfer components of the reaction centre of Rhodopseudomonas viridis. Oxidation--reduction potentials and interactions of the electron acceptors.

Oxidation-reduction potentiometry was carried out on Rhodopseudomonas viridis chromatophores. Measurements of e.p.r. signals of the semiquinone-iron type at g=1.82 have revealed a more complex situation than previously reported. The presence of three different components is indicated. The midpoint potential (E(m)) of the primary acceptor quinone/semiquinone couple was found to be approx. -165mV at pH10, with a pK being reached at around pH7.5. The primary acceptor also accepts a second electron with an E(m) of -525mV, but this redox transition exhibits a hysteresis effect. Interaction effects indicate the presence of another component with E(m) values at pH10 of approx. -165mV (pK reached at around pH7.5) for single reduction and -350mV (pK at pH10 or greater) for double reduction. It is suggested that this component is the secondary acceptor. Another semiquinone-iron-type component which gives a g=1.82 signal is also present. This component is distinguishable from the primary acceptor by its e.p.r. spectrum, which shows a double peak at g=1.82 and a g(x) line at g=1.76. This component has E(m) values at pH10 for single and double reduction of -15mV and approx. -150mV respectively. Both of these E(m) values are pH-dependent. The presence of an interaction between this component and the photoreduced primary acceptor indicates the close proximity of these components. However, the midpoint potential of this component indicates a function as a secondary electron-transport component rather than an electron acceptor in the reaction centre. The dependence of the bacteriopheophytin intermediate (I) doublet e.p.r. signal on the presence of the semiquinone-iron form of the primary acceptor is demonstrated. The midpoint potential of the I/I(-) couple is estimated to be lower than -600mV.

Bacterial Chromatophores↗