Interfacial instability and the agglutination of erythrocytes by polylysine

Human erythrocytes have been exposed to poylysine of molecular weight range 4 to 220 kDa and concentration range 0.5 to 2,000 /ml at 37°C. Threshold concentrations for cell agglutination by the polycation have been determined for the samples of different molecular weight. Light and electron micrographs show that, in the erythrocyte agglutinates, cell-cell contact is generally made only at discrete, spatially periodic, regions which are distributed over a significant part of the cell surface. The average spacing between contact regions is 0.83 m. The cell membrane has a wavy profile between contact regions. Agglutination occurs only in cell samples whose electrophoretic mobility is significantly altered by polylysine and, in agreement with a previous report, occurs even when the electrophoretic mobility reaches high positive values. The electrophoretic mobility data implies that agglutination requires some protrusion of polylysine from the cell glycocalyx. We discuss how a resulting net attractive intercellular force could act to destabilize the aqueous layer between two cells, allowing surface wave growth which results in spatially periodic contact regions. Examples of situations where cell and membrane contact might be explained by the general concept of interfacial instability are discussed.     

Influence of diabetes on natriuretic peptide thresholds in screening for Stage B heart failure

Context: Natriuretic peptide (NP) has been shown to be an effective screening tool to identify patients with Stage B heart failure and to have clinical value in preventing heart failure progression. The impact of associated metabolic confounders on the screening utility of NP needs clarification.

Objective: To assess the impact of diabetes mellitus (DM) on NP screening for asymptomatic Stage B heart failure.

Materials and methods: The study population consisted of 1368 asymptomatic patients with cardiovascular risk factors recruited from general practice as part of the STOP-HF trial. B-type NP (BNP) was quantified at point-of-care.

Results: BNP was found to be as accurate for detecting Stage B heart failure in DM patients compared to non-DM patients (AUC 0.75 [0.71,0.78] and 0.77 [0.72,0.82], respectively). However, different BNP thresholds are required to achieve the same level of diagnostic sensitivity in DM compared with non-DM patients. To achieve 80% sensitivity a difference of 5-ng/L lower is required for patients with DM.

Conclusion: Although a significantly different BNP threshold is detected for patients with DM, the BNP concentration difference is small and unlikely to warrant a clinically different diagnostic threshold.     

Intrinsic electric fields and membrane bending

The fragmentation of human erythrocytes heated in a range of ionic environments has been examined by video microscopy, , the average number of surface wave crests growing on the cell rim during fragmentation by membrane externalization, andI, the percentage of cells internalizing membrane, were scored.The membrane diffusion potential was altered experimentally on decreasing the extracellular chloride concentration by substituting either membrane-impermeant sorbitol or Na gluconate for some NaCl. The external-membrane-face surface potential was altered either by surface charge depletion or by ionic strength changes. The dependence of morphological change on diffusion potential at constant cell volume and surface potentials was established over a 34-mV change in diffusion potential. The rate constants for morphological change with charge depletion at different diffusion potentials are largely independent of the diffusion potential. A l.O-mV increase in diffusion potential has an effect on morphological change of comparable magnitude to that of a 1.0-mV decrease in the modulus of the negative surface potential. When the diffusion potential increased on decreasing both the extracellular diffusible ion concentration and extracellular ionic strength, the effect on cell morphology of increasing the modulus of the surface potential was overcome by the effects of the diffusion potential change.     

Metagenomic analysis of a stable trichloroethene-degrading microbial community

Dehalococcoides bacteria are the only organisms known to completely reduce chlorinated ethenes to the harmless product ethene. However, Dehalococcoides dechlorinate these chemicals more effectively and grow more robustly in mixed microbial communities than in isolation. In this study, the phylogenetic composition and gene content of a functionally stable trichloroethene-degrading microbial community was examined using metagenomic sequencing and analysis. For phylogenetic classification, contiguous sequences (contigs) longer than 2500 bp were grouped into classes according to tetranucleotide frequencies and assigned to taxa based on rRNA genes and other phylogenetic marker genes. Classes were identified for Clostridiaceae, Dehalococcoides, Desulfovibrio, Methanobacterium, Methanospirillum, as well as a Spirochete, a Synergistete, and an unknown Deltaproteobacterium. Dehalococcoides contigs were also identified based on sequence similarity to previously sequenced genomes, allowing the identification of 170 kb on contigs shorter than 2500 bp. Examination of metagenome sequences affiliated with Dehalococcoides revealed 406 genes not found in previously sequenced Dehalococcoides genomes, including 9 cobalamin biosynthesis genes related to corrin ring synthesis. This is the first time that a Dehalococcoides strain has been found to possess genes for synthesizing this cofactor critical to reductive dechlorination. Besides Dehalococcoides, several other members of this community appear to have genes for complete or near-complete cobalamin biosynthesis pathways. In all, 17 genes for putative reductive dehalogenases were identified, including 11 novel ones, all associated with Dehalococcoides. Genes for hydrogenase components (271 in total) were widespread, highlighting the importance of hydrogen metabolism in this community. PhyloChip analysis confirmed the stability of this microbial community.     

Effect of mazindol on dystrophic mice and on growth in young rats

1. Mazindol, which has been proposed as a therapy for muscular dystrophy because of a suppression of growth hormone release was administered orally (0.1 mg/kg body wt/day) for approximately six weeks to healthy young rats and dystrophic mice. 2. Mazindol had no effect on the dystrophic mice. 3. Mazindol treated rats had reduced wt gain, but this effect was due to appetite suppression not growth hormone inhibition. 4. No effect of mazindol was seen on rat muscle, but there were significant increases in liver, heart and kidney wts compared to controls.     

Exploring mixed microbial community functioning: recent advances in metaproteomics

System approaches to elucidate ecosystem functioning constitute an emerging area of research within microbial ecology. Such approaches aim at investigating all levels of biological information (DNA, RNA, proteins and metabolites) to capture the functional interactions occurring in a given ecosystem and track down characteristics that could not be accessed by the study of isolated components. In this context, the study of the proteins collectively expressed by all the microorganisms present within an ecosystem (metaproteomics) is not only crucial but can also provide insights into microbial functionality. Overall, the success of metaproteomics is closely linked to metagenomics, and with the exponential increase in the availability of metagenome sequences, this field of research is starting to experience generation of an overwhelming amount of data, which requires systematic analysis. Metaproteomics has been employed in very diverse environments, and this review discusses the recent advances achieved in the context of human biology, soil, marine and freshwater environments as well as natural and bioengineered systems.