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PubMed1986

An experimental test of new theoretical models for the electrokinetic properties of biological membranes. The effect of UO2++ and tetracaine on the electrophoretic mobility of bilayer membranes and human erythrocytes.

For a large smooth particle with charges at the surface, the electrophoretic mobility is proportional to the zeta potential, which is related to the charge density by the Gouy-Chapman theory of the diffuse double layer. This classical model adequately describes the dependence of the electrophoretic mobility of phospholipid vesicles on charge density and salt concentration, but it is not applicable to most biological cells, for which new theoretical models have been developed. We tested these new models experimentally by measuring the effect of UO2++ on the electrophoretic mobility of model membranes and human erythrocytes in 0.15 M NaCl at pH 5. We used UO2++ for these studies because it should adsorb specifically to the bilayer surface of the erythrocyte and should not change the density of fixed charges in the glycocalyx. Our experiments demonstrate that it forms high-affinity complexes with the phosphate groups of several phospholipids in a bilayer but does not bind significantly to sialic acid residues. As observed previously, UO2++ adsorbs strongly to egg phosphatidylcholine (PC) vesicles: 0.1 mM UO2++ changes the zeta potential of PC vesicles from 0 to +40 mV. It also has a large effect on the electrophoretic mobility of vesicles formed from mixtures of PC and the negative phospholipid phosphatidylserine (PS): 0.1 mM UO2++ changes the zeta potential of PC/PS vesicles (10 mol % PS) from -13 to +37 mV. In contrast, UO2++ has only a small effect on the electrophoretic mobility of either vesicles formed from mixtures of PC and the negative ganglioside GM1 or erythrocytes: 0.1 mM UO2++ changes the apparent zeta potential of PC/GM1 vesicles (17 mol % GM1) from -11 to +5 mV and the apparent zeta potential of erythrocytes from -12 to -4 mV. The new theoretical models suggest why UO2++ has a small effect on PC/GM1 vesicles and erythrocytes. First, large groups (e.g., sugar moieties) protruding from the surface of the PC/GM1 vesicles and erythrocytes exert hydrodynamic drag. Second, charges at the surface of a particle (e.g., adsorbed UO2++) exert a smaller effect on the mobility than charges located some distance from the surface (e.g., sialic acid residues).

Electrophoresis↗
PubMed1997

Unusual lack of internal mobility and fast overall tumbling in oxidized flavodoxin from Anacystis nidulans.

Anacystis nidulans flavodoxin, an electron-transfer protein containing a flavin mononucleotide (FMN) molecule as its prosthetic group, has a redox potential for the oxidized/semiquinone equilibrium close to that of free flavin. Whereas the redox potential for the semiquinone/hydroquinone equilibrium is more negative. To gain an understanding of the contribution of mobility to redox potential modulation, we studied the backbone mobility of the oxidized A. nidulans flavodoxin at pH 6.6, 303 K by 15N NMR relaxation measurements. The spin-lattice relaxation rate constants (RN(Nz)=1/T1), spin-spin relaxation rate constants (RN(Nx,y)=1/T2) and 1H-15N nuclear Overhauser effects (NOE) were obtained for 143 of the 166 protonated backbone 15N nuclei and for the FMN N3 nucleus without ambiguity. The 15N T1, T2 and NOE data were analyzed by reduced spectral density mapping, and the so-called model-free approach. In contrast to most other proteins studied with 15N relaxation experiments, we found an almost complete absence of internal mobility. The overall correlation time of this 169-residue flavodoxin (>19 kDa) is significantly shorter (7.4 to 7.8 ns) than that of other proteins of this size, suggesting that the absence of internal mobility is correlated with faster overall rotational diffusion. The uniformity of the motional parameters along the backbone is in strong contrast to the crystallographic B-factors, which vary significantly along the sequence in this and other flavodoxins. The NMR relaxation parameters are primarily sensitive to rotational diffusive motions of the N-H bond vectors, while the crystallographic B-factors would be sensitive to translational internal motions as well. However, the large B-factors in this protein may originate from crystal packing and crystal lattice disorder. The relatively fast overall tumbling results in sharp NMR resonances. Hence, much larger proteins with such favorable dynamic behavior could be excellent candidates for studies by NMR.

Computer Simulation↗
PubMed2003

Dissipation of the herbicide oxyfluorfen in subtropical soils and its potential to contaminate groundwater.

The dissipation and mobility of the herbicide oxyfluorfen (2-chloro-alpha,alpha,alpha-trifluoro-p-tolyl 3-ethoxy-4-nitrophenyl ether) in field soil of Taiwan were investigated in the laboratory with six tea garden soils. The dissipation coefficients of oxyfluorfen in soils of different moisture content (30%, 60%, and 90% of soil field capacity) and soil temperature (10 degrees C, 25 degrees C, and 40 degrees C) were studied. Results indicate that the half-life of oxyfluorfen ranged from 72 to 160 days for six tea garden soils. It was found that if the temperature is high, the dissipation rate is rapid, and there is almost no dissipation at 10 degrees C. Possible contamination of groundwater by the herbicide oxyfluorfen was assessed using the behavior assessment model and the groundwater pollution-potential (GWP) model. The results obtained after evaluating the residue and travel time using the GWP model illustrated that oxyfluorfen is not very mobile in soil and may not contaminate groundwater under normal conditions. But in the case of soil of extremely low organic carbon content and coarse texture, oxyfluorfen has the potential to contaminate groundwater less than 3m deep.

Environmental Monitoring↗
PubMed1989

[Value of the study of the functional potential of neutrophils in suppurative, septic and allergic diseases in children].

A method for measuring the content of cationic proteins in neutrophil granulocytes of the peripheral blood was employed in patients with pyoseptic (n = 12) and allergic (n = 28) diseases during the exposure to composite infections in vitro. The method enables one to assess the functional potentialities of the cells in mobilizing the internal reserves and the readiness for the trigger of the cellular granular apparatus, for instance during real or predicted exposure of the child to bacterial infections. The determination of the functional potentialities of neutrophil phagocytes can be used as a test for the appraisal of the gravity of allergic and pyoseptic processes as well as for predicting outcomes of pyoseptic diseases.

Adolescent↗
PubMed2006

On the nature of liquid junction and membrane potentials.

Whenever a spatially inhomogeneous electrolyte, composed of ions with different mobilities, is allowed to diffuse, charge separation and an electric potential difference is created. Such potential differences across very thin membranes (e.g. biomembranes) are often interpreted using the steady state Goldman equation, which is usually derived by assuming a spatially constant electric field. Through the fundamental Poisson equation of electrostatics, this implies the absence of free charge density that must provide the source of any such field. A similarly paradoxical situation is encountered for thick membranes (e.g. in ion-selective electrodes) for which the diffusion potential is normally interpreted using the Henderson equation. Standard derivations of the Henderson equation appeal to local electroneutrality, which is also incompatible with sources of electric fields, as these require separated charges. We analyse self-consistent solutions of the Nernst-Planck-Poisson equations for a 1 : 1-univalent electrolyte to show that the Goldman and Henderson steady-state membrane potentials are artefacts of extraneous charges created in the reservoirs of electrolyte solution on either side of the membrane, due to the unphysical nature of the usual (Dirichlet) boundary conditions assumed to apply at the membrane-electrolyte interfaces. We also show, with the aid of numerical simulations, that a transient electric potential difference develops in any confined, but initially non-uniform, electrolyte solution. This potential difference ultimately decays to zero in the real steady state of the electrolyte, which corresponds to thermodynamic equilibrium. We explain the surprising fact that such transient potential differences are well described by the Henderson equation by using a computer algebra system to extend previous steady-state singular perturbation theories to the time-dependent case. Our work therefore accounts for the success of the Henderson equation in analysing experimental liquid-junction potentials.

Computer Simulation↗
PubMed2006

Evidence-based policy? The use of mobile phones in hospital.

BACKGROUND: Evidence-based policies have become increasingly accepted in clinical practice. However, policies on many of the non-clinical activities that take place in health care facilities may be less frequently evidence based. METHODS: We carried out a review of literature on safety of mobile phones in hospitals and survey of practice in selected European countries. RESULTS: When first evidence on the dangers of electronic interference associated with mobile phones appeared in the 1990s, hospitals in many countries introduced complete bans on mobile phones. Yet a review of recent evidence suggests that there is no significant risk from using mobile phones in hospitals as long as they are more than a metre away from sensitive equipment, whereas the risk to the most modern equipment is even less. With the technological evolution of mobile phones, the residual risk of interference appears to be minimal and controllable. Although some countries are reluctant to relax regulation, others now limit bans to areas in which sensitive equipment is used and some discourage the use of mobile phones on the grounds of noise exposure. CONCLUSION: With new technology on the doorstep, the potential benefits and risks associated with mobile phones should be examined explicitly in the light of the evidence.

Cell Phone↗
PubMed1991

Engagement of MHC-class II molecules by staphylococcal exotoxins delivers a comitogenic signal to human B cells.

The staphylococcal exotoxin toxic shock syndrome toxin-1 (TSST-1) has been demonstrated to bind to monomorphic determinants on MHC-class II molecules. In this study, we have used TSST-1 to probe the role of MHC-class II molecules in the activation and differentiation of resting human B cells. Highly purified B cells were stimulated with TSST-1, alone or in combination with PMA or with anti-human IgM antibodies (anti-mu) and the resulting B cell proliferation and Ig production were monitored. On its own, TSST-1 failed to induce B cell proliferation or Ig production. However, TSST-1 synergized with PMA and with anti-mu in inducing B cell proliferation in the absence of any added T cells or T cell factors. TSST-1 did not induce or potentiate early activation events associated with anti-mu treatment such as phosphoinositide hydrolysis and Ca2+ mobilization. Also, TSST-1 did not potentiate the capacity of anti-mu to induce the transcription of early activation genes such as c-myc. Finally, in contrast to its capacity to promote mitogen-trigered B cell proliferation, TSST-1 failed to induce the differentiation of B lymphocytes into Ig-secreting cells in the absence of added T cells. These results indicate that TSST-1 delivers a comitogenic signal to B cells via MHC-class II molecules that is distinct from signals delivered via surface mu and further strengthens the role of MHC-class II molecules as signal transducing structures.

Antibodies, Anti-Idiotypic↗
PubMed2003

Characterization of poly(ethylene oxide) brushes on glass surfaces and adhesion of Staphylococcus epidermidis.

Poly(ethylene oxide) brushes have been covalently bound to glass surfaces and their presence was demonstrated by an increase in water contact angles from fully wettable on glass to advancing contact angles of 54 degrees, with a hysteresis of 32 degrees. In addition, electrophoretic mobilities of glass and brush-coated glass were determined using streaming potential measurements. The dependence of the electrophoretic mobilities on the ionic strength was analyzed in terms of a softlayer model, yielding an electrophoretic softness and fixed charge density of the layer. Brush-coated glass could be distinguished from glass by a 2-3-fold decrease in fixed charge density, while both surfaces were about equally soft. Adhesion of Staphylococcus epidermidis HBH276 to glass in a parallel plate flow chamber was extremely high and after 4 h, 19.0 x 10(6) bacteria were adhering per cm2. In contrast, the organisms did not adhere to brush-coated glass, with numbers below the detection limit, i.e. 0.1 x 10(6) per cm2. These results attest to the great potential of polymer brushes in preventing bacterial adhesion to surfaces.

Bacterial Adhesion↗
PubMed2003

High mobility group A1 is expressed in metastatic adenocarcinoma to the liver and intrahepatic cholangiocarcinoma, but not in hepatocellular carcinoma: its potential use in the diagnosis of liver neoplasms.

BACKGROUND: An increased level of high mobility group A (HMGA) gene/protein expression has been demonstrated to be associated with many human neoplasms originating from a variety of tissues. However, HMGA1 expression has not yet been studied in hepatic tumors. In this study, we analyzed HMGA1 expression in hepatic primary and metastatic tumors in order to verify whether determination of the HMGA1 expression level could provide any diagnostic advantages in the pathological diagnosis of hepatic tumors. METHODS: Twenty samples of hepatocellular carcinoma, 5 samples of intrahepatic cholangiocarcinoma, and 21 samples of metastatic adenocarcinoma to the liver (15 metastatic tumors from colorectal carcinoma and 6 metastatic tumors from pancreatic carcinoma) were analyzed immunohistochemically using an HMGA1-specific antibody. RESULTS: While no significant nuclear immunoreactivity was found in hepatocytes of non-neoplastic liver tissue, 40% (2/5) of intrahepatic cholangiocarcinomas, 53.3% (8/15) of metastatic lesions from colorectal carcinoma, and 100% (6/6) of metastatic lesions from pancreatic carcinoma showed positive immunoreactivity. In contrast, all 20 samples of hepatocellular carcinoma were negative for HMGA1 nuclear immunoreactivity. Thus, hepatocellular carcinoma represents the first case of malignant neoplasia in which HMGA1 expression is not induced, which presents a striking contrast to several previous studies demonstrating the significance of increased HMGA gene/protein levels in carcinogenesis and/or tumor progression. CONCLUSIONS: Based on these findings, we conclude that the HMGA1 protein level could serve as a potential diagnostic marker that may enable the differential diagnosis between hepatocellular carcinoma and intrahepatic cholangiocarcinoma or metastatic adenocarcinoma to the liver.

Bile Duct Neoplasms↗
PubMed2004

Olf/EBF proteins are expressed in neuroblastoma cells: potential regulators of the Chromogranin A and SCG10 promoters.

The childhood malignancy neuroblastoma is derived from developmentally arrested sympathetic nervous system precursor cells. To obtain further insight into the molecular processes involved in the formation of these tumors, we decided to investigate the functional role of Olf/EBF (O/E) transcription factors in human neuroblastoma cells. We here report that O/E-1 and O/E-2 are expressed at variable levels in neuroblastoma cell lines and that O/E proteins could be identified by electrophoretic mobility shift assays. To identify potential neuronal target genes for O/E proteins in neuroblastoma cells we investigated the ability of a set of neuronal promoters to interact with O/E-1 in electrophoretic mobility shift assays. This analysis suggested that the Chromogranin A (CgA) and SCG10 promoters both contained binding sites for O/E-1. O/E-1 was able to activate the CgA promoter in vivo and mutation of the O/E-1 binding site in the CgA promoter reduced the functional activity of the element to about 60% of the wild-type in neuroblastoma cells, supporting the idea that O/E proteins may be involved in the control of the CgA promoter. Furthermore, overexpression of O/E-1 in hippocampal progenitor cells led to neurite outgrowth, indicative of a role for O/E proteins in neuronal differentiation.

Binding Sites↗
PubMed2005

Arsenic mobilization through microbially mediated deflocculation of ferrihydrite.

This study examined the potential impact of microbially mediated reduction of Fe in the Fe(III)-(hydr)oxide mineral ferrihydrite on the mobility of As in natural waters. In microcosm experiments, the obligately anaerobic bacterium Geobacter metallireducens reduced on average 10% of the Fe(III) in ferrihydrite with varying sorbed As(V) surface coverages, which resulted in deflocculation of initially micron-sized As-bearing ferrihydrite aggregates to nanometersized colloids. No reduction of As(V) to As(III) was observed in microcosm samples. Measurement of Fe and As within operationally defined particulate, colloidal, and dissolved fractions of microcosm slurry samples revealed that little Fe or As was released from ferrihydrite as dissolved species. Microbially induced deflocculation of ferrihydrite in the presence of G. metallireducens was correlated with more negative zeta potential of ferrihydrite nanoparticles suggesting that G. metallireducens mediated As mobilization through alteration of ferrihydrite surface charge. TEM analysis and solution chemistry conditions suggested formation of a magnetite surface layer through topotactic recrystallization of ferrihydrite (2LFH) driven by sorbed Fe(II). The formation of nanometer-sized As-bearing colloids through microbially mediated reduction of Fe-(hydr)oxides has the potential to increase human As exposure by enhancing As mobility in natural waters and hindering As removal during subsequent drinking water treatment.

Arsenic↗
PubMed1997

Angiotensin II potentiates vasodilation of rat aorta by cAMP elevating agonists.

We previously observed an effect of the Ca++-mobilizing peptide, angiotensin II (ANG II), to potentiate agonist-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) formation in rat cultured aortic smooth muscle cells. Consequently, it was postulated that the relaxant effects of dilator agents that act through cAMP formation would be enhanced in the presence of ANG II. To test this idea, we examined the influence of ANG II on agonist-induced relaxation of rat isolated aortic rings. Angiotensin II (0.1 microM) evoked a transient increase in the tone of KCI (30 mM)-precontracted aortae that returned to the original level of induced tension after about 20 min. Subsequent application of isoproterenol caused a concentration-dependent relaxation that was significantly greater in preparations pretreated with ANG II than in time-matched controls. Similarly, isoproterenol-induced relaxations of aortae precontracted with either phenylephrine (1 microM) or endothelin 1 (3 nM) were also augmented after ANG II treatment. The principal action of ANG II was to enhance the maximal relaxation evoked by isoproterenol without affecting the EC50 value, irrespective of the contractile agent used. This potentiating effect of ANG II was not specific for beta adrenoceptor-mediated relaxation because the relaxant response to iloprost, a prostaglandin I2 analog, was also increased after ANG II treatment. The effect of ANG II to enhance isoproterenol-induced relaxation was maintained in endothelium-denuded preparations. However, ANG II did not enhance the relaxation of vessels evoked through either the direct elevation of cAMP levels by dibutyryl cAMP or the stimulation of cyclic 3',5'-guanosine monophosphate formation by sodium nitroprusside. The data indicate that exposure of rat aortae to the constrictor peptide ANG II enhances the vasodilation of these blood vessels by agonists that stimulate cAMP formation. Such cross-talk between constrictor and dilator pathways could represent an important mechanism in the modulation of vascular tone.

Angiotensin II↗
PubMed2005

Site-specific reverse splicing of a HEG-containing group I intron in ribosomal RNA.

The wide, but scattered distribution of group I introns in nature is a result of two processes; the vertical inheritance of introns with or without losses, and the occasional transfer of introns across species barriers. Reversal of the group I intron self-splicing reaction, termed reverse splicing, coupled with reverse transcription and genomic integration potentially mediate an RNA-based intron mobility pathway. Compared to the well characterized endonuclease-mediated intron homing, reverse splicing is less specific and represents a likely explanation for many intron transpositions into new genomic sites. However, the frequency and general role of an RNA-based mobility pathway in the spread of natural group I introns is still unclear. We have used the twin-ribozyme intron (Dir.S956-1) from the myxomycete Didymium iridis to test how a mobile group I intron containing a homing endonuclease gene (HEG) selects between potential insertion sites in the small subunit (SSU) rRNA in vitro, in Escherichia coli and in yeast. Surprisingly, the results show a site-specific RNA-based targeting of Dir.S956-1 into its natural (S956) SSU rRNA site. Our results suggest that reverse splicing, in addition to the established endonuclease-mediated homing mechanism, potentially accounts for group I intron spread into the homologous sites of different strains and species.

Animals↗
PubMed2004

[High mobility group box-1 protein activates Janus kinase-signal transducer and activator of transcription pathway in rat peritoneal macrophages].

OBJECTIVE: To investigate the potential signal transduction mechanism in high mobility group box-1 protein (HMGB1)-induced inflammatory response in rat peritoneal macrophages. METHODS: Peritoneal macrophages obtained from male Wistar rats were incubated for 3 days before they were stimulated by HMGB1 (10 microg/ml). At various time points after HMGB1 stimulation, macrophages were denatured directly in cell culture flasks to detect activation of Janus kinase-2 (JAK2), signal transducer and activator of transcription-1 (STAT1) and STAT3 by immunoprecipitation, Western blotting and electrophoretic mobility shift assay, respectively. RESULTS: HMGB1 stimulation could activate STAT1 and STAT3 in peritoneal macrophages in 2 hours, among them the activation of STAT3 appeared to be the quickest, peaking as early as 10 minutes after stimulation. But no marked change in JAK2 activity was observed within 2 hours following HMGB1 stimulation. CONCLUSION: These data suggest that Janus kinase-signal transducer and activator of transcription pathway might be involved in regulation of HMGB1-induced inflammatory response in peritoneal macrophages.

Animals↗
PubMed1995

Changing migration patterns in the Federated States of Micronesia.

"This article traces the changing role of migration in the Federated States of Micronesia during the twentieth century. We begin with a brief geographical, historical, and cultural overview of each state in the country, summarizing demographic change over the past 70 years and providing a foundation for understanding much of the area's past and present human mobility. Attention then turns to migration within the Federated States, focusing on data from censuses conducted in 1930, 1973, and 1980 and using supplemental information when possible. Emigration to destinations outside the country is examined briefly. Finally, we discuss potential causes and impacts of mobility in this emerging island nation."

Demography↗
PubMed1986

Ion concentration effects on the zeta potential of bone.

Stressed bone generates an electrical potential, the sign of which reverses in the presence of specific concentrations of sodium, potassium, or calcium ions. A study was designed to test the hypotheses, drawn from stress-generated potential (SGP) studies, that the reversal in polarity of the zeta potential of bone is the cause of this SGP polarity reversal. The zeta potential of bone particles, prepared from fresh bovine metatarsals as homogeneous 5 microns dispersions, was measured by free-fluid electrophoresis in different concentrations of sodium chloride. The zeta potential of bone particles reversed sign at a sodium ion concentration that was the same as that found to reverse measured SGPs, namely 0.74 molar. This finding is consistent with the hypothesis that streaming potentials are the cause of SGPs in fluid-saturated bone. It was possible to obtain electrophoretic mobility histograms, and hence zeta-potential histograms, of bone particles by using a Pen Kem, Inc. (Bedford Hills, NY, U.S.A.) "3000" Automated Electrokinetic Analyzer. At sodium ion concentrations at which bone particles were nearly neutral, the zeta-potential histograms indicated a broad distribution of particle charge, with some particles being negative, some positive, and some neutral. In addition, it was found that particles prepared from Formalin-fixed bone produced the same electrokinetic results as those prepared from fresh bone, and that the addition of MOPS buffer caused the zeta potential to invert sign from negative to positive values at ion concentrations exceeding 3.0 molar.

Animals↗