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E Evans

Publications and source records attributed to E Evans.

At least 19 recordsLinked to original sources
PubMed1992

Equilibrium "wetting" of surfaces by membrane-covered vesicles.

"Wetting" of surfaces by thin-membrane capsules is the central process involved in coagulation of suspensions of surfactant membrane vesicles and other-related phases of microemulsions. Although equilibrium "wetting" by membrane capsules appears similar to the macroscopic wetting by liquid droplets, there are important differences: i.e. membrane tension (in place of liquid-interfacial tension) and "effective" contact angle are not fixed constants. Since membranes are condensed-cohesive materials with limited permeability, geometric restrictions (surface area and enclosed volume) are the principal determinants of the extent of contact with a substrate (and "effective contact angle) for "strong" adhesion energies. Deviation from this universal feature arises when membrane-membrane attraction becomes sufficient to compete with membrane-substrate attraction; a transition is predicted from maximal contact with the substrate to partial substrate contact plus membrane lamination by self adhesion. Following the transition, the "effective" contact angle is determined by the ratio of self adhesion: substrate adhesion energies. A critical condition is established for the transition by the area excess (over a sphere of equivalent volume). Because of the exceptional flexibility of fluid membranes, thermal excitations produce long-wavelength collective motions and significant shape fluctuations. Restriction of fluctuations (by area: volume constraints and adhesion) lead to unconventional elastic response and crossover from "strong" to "weak" regimes of equilibrium "wetting" for membrane capsules.

Capsules↗
PubMed1992

Characterization of vaccinia virus DNA replication mutants with lesions in the D5 gene.

The vaccinia virus D5 gene encodes a 90 kDa early protein that is essential for viral DNA replication. In this report we map and explore the phenotypes of the temperature sensitive mutants bearing lesions in this gene: ts17, ts24, ts69 (WR strain) and ts6389 (IHD strain). Viral DNA synthesis was virtually undetectable during non-permissive infections performed with ts17, and incorporation of 3H-thymidine ceased rapidly when cultures were shifted to the non-permissive temperature in the midst of replication. The D5 protein may therefore be involved in DNA synthesis at the replication fork. The lesions of the four mutants were localized within the D5 orf by marker rescue, and the single nucleotide changes responsible for the ts phenotype of the three WR mutants were identified. Unexpectedly, the three alleles with N-terminal mutations were impaired in marker rescue when homologous recombination with small (< 2 kb), intragenic DNA fragments at 39.5 degrees C was required. This deficiency was not due to degradation of transfected DNA under non-permissive conditions. Efficient marker rescue could be restored by incubation at the permissive temperature for a brief period after transfection, suggesting a requirement for functional D5 in genome/plasmid recombination. Marker rescue under non-permissive conditions could alternatively be restored by co-transfection of unlinked but contiguous DNA sequences.

Alleles↗
PubMed1992

Growth-rate-independent killing by ciprofloxacin of biofilm-derived Staphylococcus epidermidis; evidence for cell-cycle dependency.

Cell culture methods that allow culture of Staphylococcus epidermidis biofilms at controlled growth rates were used to examine susceptibility to ciprofloxacin. Changes in biofilm susceptibility, dependent upon growth rate, were compared with those for suspended populations grown in chemostat, and also for newly-formed daughter cells shed from the biofilm during its growth and development. Susceptibility increased for intact and resuspended biofilms, and also for planktonic cultures, with increases in growth rate. The dependence of susceptibility upon growth rate was greatest for slow growing cells (mu, 0.01-0.15/h). At any particular growth rate, biofilms appeared more susceptible than their planktonic counterparts. Newly-formed daughter cells were relatively tolerant to ciprofloxacin at all rates of growth. Lack of growth rate dependency for the newly-formed cells suggested a role for the cell-division cycle in determining resistance. This was confirmed by examining the susceptibility of S. epidermidis throughout batch cultures with cell division synchronized. Perfusion of various steady-state biofilms with ciprofloxacin demonstrated killing of the adherent population even at much reduced rates of growth.

Bacterial Adhesion↗
PubMed1992

Effect of biofilm culture upon the susceptibility of Staphylococcus epidermidis to tobramycin.

Biofilms of Staphylococcus epidermidis were cultured at various specific growth rates, and susceptibilities to tobramycin were compared with those of equivalent plank-tonic populations. In all instances, susceptibility increased significantly with increasing specific growth rate. However, resuspension of the biofilms increased susceptibility, suggesting some involvement of the glycocalyx in reducing antibiotic permeation of the biofilm. Cells that dispersed spontaneously from the biofilms at steady state were particularly susceptible to this agent. Since such cells correspond to newly-divided daughter cells, the relationship between tobramycin susceptibility and the phase in the division cycle was investigated. Susceptibility was enhanced in cultures dividing synchronously shortly before, during and shortly after cell separation. Perfusion of actively-growing S. epidermidis biofilms with tobramycin also demonstrated increased susceptibility with increasing growth rate, but also showed rapid recovery following removal of the agent.

Ciprofloxacin↗
PubMed1992

Hoarseness after tracheal intubation.

The reported incidence of hoarseness following short-term tracheal intubation varies widely. It has been reported as being permanent in 3%. This suggests that an enormous problem exists considering the numbers of patients intubated daily in the United Kingdom. A prospective study of 235 adult patients undergoing general anaesthesia in a district general hospital included 167 patients whose tracheas were intubated. Of these 167, 54 (32%) complained of hoarseness postoperatively. All but five returned to normal within 7 days. The others were hoarse for 9, 10, 12, 54 and 99 days. Those who were hoarse for 54 and 99 days had vocal cord granulomata. Regression analyses showed that certain patient and anaesthetic factors had a significant effect on the hoarseness. This study confirms a low incidence of prolonged or permanent hoarseness following short-term tracheal intubation.

Adolescent↗
PubMed1991

Detachment of agglutinin-bonded red blood cells. I. Forces to rupture molecular-point attachments.

A simple micromechanical method has been developed to measure the rupture strength of a molecular-point attachment (focal bond) between two macroscopically smooth membrane capsules. In the procedure, one capsule is prepared with a low density coverage of adhesion molecules, formed as a stiff sphere, and held at fixed position by a micropipette. The second capsule without adhesion molecules is pressurized into a spherical shape with low suction by another pipette. This capsule is maneuvered to initiate point contact at the pole opposite the stiff capsule which leads to formation of a few (or even one) molecular attachments. Then, the deformable capsule is slowly withdrawn by displacement of the pipette. Analysis shows that the end-to-end extension of the capsule provides a direct measure of the force at the point contact and, therefore, the rupture strength when detachment occurs. The range for point forces accessible to this technique depends on the elastic moduli of the membrane, membrane tension, and the size of the capsule. For biological and synthetic vesicle membranes, the range of force lies between 10(-7)-10(-5) dyn (10(-12)-10(-10) N) which is 100-fold less than presently measurable by Atomic Force Microscopy! Here, the approach was used to study the forces required to rupture microscopic attachments between red blood cells formed by a monoclonal antibody to red cell membrane glycophorin, anti-A serum, and a lectin from the snail-helix pomatia. Failure of the attachments appeared to be a stochastic function of the magnitude and duration of the detachment force. We have correlated the statistical behavior observed for rupture with a random process model for failure of small numbers of molecular attachments. The surprising outcome of the measurements and analysis was that the forces deduced for short-time failure of 1-2 molecular attachments were nearly the same for all of the agglutinin, i.e., 1-2 x 10(-6) dyn. Hence, microfluorometric tests were carried out to determine if labeled agglutinins and/or labeled surface molecules were transferred between surfaces after separation of large areas of adhesive contact. The results showed that the attachments failed because receptors were extracted from the membrane.

ABO Blood-Group System↗
PubMed1991

Detachment of agglutinin-bonded red blood cells. II. Mechanical energies to separate large contact areas.

As detailed in a companion paper (Berk, D., and E. Evans. 1991. Biophys. J. 59:861-872), a method was developed to quantitate the strength of adhesion between agglutinin-bonded membranes without ambiguity due to mechanical compliance of the cell body. The experimental method and analysis were formulated around controlled assembly and detachment of a pair of macroscopically smooth red blood cell surfaces. The approach provides precise measurement of the membrane tension applied at the perimeter of an adhesive contact and the contact angle theta c between membrane surfaces which defines the mechanical leverage factor (1-cos theta c) important in the definition of the work to separate a unit area of contact. Here, the method was applied to adhesion and detachment of red cells bound together by different monoclonal antibodies to red cell membrane glycophorin and the snail-helix pomatia-lectin. For these tests, one of the two red cells was chemically prefixed in the form of a smooth sphere then equilibrated with the agglutinin before the adhesion-detachment procedure. The other cell was not exposed to the agglutinin until it was forced into contact with the rigid cell surface by mechanical impingement. Large regions of agglutinin bonding were produced by impingement but no spontaneous spreading was observed beyond the forced contact. Measurements of suction force to detach the deformable cell yielded consistent behavior for all of the agglutinins: i.e., the strength of adhesion increased progressively with reduction in contact diameter throughout detachment. This tension-contact diameter behavior was not altered over a ten-fold range of separation rates. In special cases, contacts separated smoothly after critical tensions were reached; these were the highest values attained for tension. Based on measurements reported in another paper (Evans et al. 1991. Biophys. J. 59:838-848) of the forces required to rupture molecular-point attachments, the density of cross-bridges was estimated with the assumption that the tension was proportional to the discrete rupture force x the number of attachments per unit length. These estimates showed that only a small fraction of agglutinin formed cross-bridges at initial assembly and increased progressively with separation. When critical tension levels were reached, it appeared that nearly all local agglutinin was involved as cross-bridges. Because one cell surface was chemically fixed, receptor accumulation was unlikely; thus, microscopic "roughness" and steric repulsion probably modulated formation of cross-bridges on initial contact. To counter the steric repulsion, adhesive contacts were exposed to solutions of a high molecular weight polymer to draw the surfaces together by osmotic dehydration of the adhesion gap. These stresses exceeded initial mechanical assembly stresses by up to three orders of magnitude. As expected, the strength of adhesion was greatly enhanced by the added impingement stress.

Animals↗
PubMed1991

Detachment of agglutinin-bonded red blood cells. III. Mechanical analysis for large contact areas.

An experimental method and analysis are introduced which provide direct quantitation of the strength of adhesive contact for large agglutinin-bonded regions between macroscopically smooth membrane capsules (e.g., red blood cells). The approach yields intrinsic properties for separation of adherent regions independent of mechanical deformation of the membrane capsules during detachment. Conceptually, the micromechanical method involves one rigid test-capsule surface (in the form of a perfect sphere) held fixed by a micropipette and a second deformable capsule maneuvered with another micropipette to force contact with the test capsule. Only the test capsule is bound with agglutinin so that the maximum number of cross-bridges can be formed without steric interference. Following formation of a large adhesion region by mechanical impingement, the deformable capsule is detached from the rigid capsule surface by progressive aspiration into the micropipette. For the particular case modeled here, the deformable capsule is assumed to be a red blood cell which is preswollen by slight osmotic hydration before the test. The caliber of the detachment pipette is chosen so that the capsule will form a smooth cylindrical "piston" inside the pipette as it is aspirated. Because of the high flexibility of the membrane, the capsule naturally seals against the tube wall by pressurization even though it does not adhere to the glass. This arrangement maintains perfect axial symmetry and prevents the membrane from folding or buckling. Hence, it is possible to rigorously analyze the mechanics of deformation of the cell body to obtain the crucial "transducer" relation between pipette suction force and the membrane tension applied directly at the perimeter of the adhesive contact. Further, the geometry of the cell throughout the detachment process is predicted which provides accurate specification of the contact angle theta c between surfaces at the perimeter of the contact. A full analysis of red cell capsules during detachment has been carried out; however, it is shown that the shear rigidity of the red cell membrane can often be neglected so that the red cell can be treated as if it were an under filled lipid bilayer vesicle. From the analysis, the mechanical leverage factor (1-cos theta c) and the membrane tension at the contact perimeter are determined to provide a complete description of the local mechanics of membrane separation as functions of large-scale experimental variables (e.g., suction force, contact diameter, overall cell length). In a companion paper (Evans, E., D. Berk, A. Leung, and N. Mohandas. 1990. Biophys. J. 59:849-860), this approach was applied to the study of separation of large regions of adhesive contact formed between red blood cells by monoclonal antibodies and lectins.

Cell Adhesion↗
PubMed1991

Intergenerational Partners Project: a model linking elementary students with senior center volunteers.

Age-integrated programming has become an effective way to bring the young and old closer together. This paper describes a 9-month intergenerational program designed to establish a more intimate involvement between a group of 4th graders and elderly volunteers from Senior Neighbors. The format used to organize the project is presented, and ongoing activities and program benefits are identified. The goals of this project have been richly met, reducing students' fears and misconceptions about aging and providing a satisfying experience for the seniors.

Aged↗
PubMed1991

Surface characteristics and adhesion of Escherichia coli and Staphylococcus epidermidis.

Surface hydrophobicity, surface electrokinetic potential and the ability to adhere to nitric-acid cleansed glass surfaces has been assessed throughout the growth, in batch culture, of Escherichia coli and Staphylococcus epidermidis. In both instances adhesiveness and surface hydrophobicity decreased in early- to mid-exponential phase. Cell surface charge, on the other hand became more electro-negative for E. coli but electro-neutral for Staph. epidermidis as the cells proceeded to divide. Adhesiveness correlated directly with surface electronegativity and hydrophobicity for Staph. epidermidis but inversely with surface electro-negativity for E. coli.

Bacterial Adhesion↗
PubMed1990

Temperature-sensitive vaccinia virus mutants identify a gene with an essential role in viral replication.

Vaccinia virus mutants ts2 and ts25, members of the same complementation group, exhibit a temperature-dependent arrest at the stage of viral DNA replication. The lesions responsible for the mutant phenotypes have been localized to the far left region of the HindIII B genomic fragment by marker rescue studies. Hybrid selection analyses established that the DNA fragments positive for rescue represented the first open reading frame of the HindIII B fragment and encoded a 30-kilodalton protein. The gene is expressed early after infection as a rightwardly transcribed 1-kilobase-pair mRNA whose coordinates were determined by S1 nuclease mapping. To further the phenotypic analysis of the mutants, the accumulation of viral DNA sequences during permissive and nonpermissive infections was quantitated. The extent of the DNA- phenotype was shown to vary in different cell types. In mouse L cells at either high or low multiplicity of infection, nonpermissive DNA synthesis was less than 5% of that seen in permissive infections. This severe defect was mirrored by correspondingly low viral yields. In infections of BSC40 monkey cells, however, the deficiencies in both DNA synthesis and virus production were far less severe. For one mutant (ts2), the temperature sensitivity in BSC40 cells varied inversely with the multiplicity of infection.

Animals↗
PubMed1989

Kinetics of granulocyte phagocytosis: rate limited by cytoplasmic viscosity and constrained by cell size.

Micromanipulation of yeast particles and blood granulocytes has been used to study the kinetics of single phagocytosis events. The ingestion process was quantitated by observation of sequential adhesion and encapsulation times. Both adherence and encapsulation times were found to increase greatly as the temperature was reduced below 37 degrees C; calcium in solution facilitated adhesion of the particle to the phagocyte but not encapsulation; both adhesion and encapsulation processes required a minimum level of plasma components (presumably complement). The general nature of these observations were confirmatory of previous studies, but this study is unique in that the specific time course of single particle ingestion was quantitated. It was immediately apparent that the phagocytosis process was 100% efficient above the threshold concentrations required for plasma and temperature, but variations in times from cell to cell indicated heterogeneity in the population. The total time for ingestion varied from as low as 2 sec/particle at 37 degrees C to above several min/particle below 15 degrees C. Encapsulation times for particles were normalized by estimates of particle surface areas to establish a specific time/unit area of particle surface: from 0.5 sec/10(-8) cm2 at 37 degrees C to greater than 8 sec/10(-8) cm2 at 15 degrees C. The temperature dependence of the encapsulation time correlated well with the temperature dependence of the "apparent" viscosity for granulocytes measured by micropipet aspiration. As such, the kinetic properties observed in these phagocytosis tests are consistent with a model that both assembly of the contractile system and the displacement of the surface by active contraction in phagocytosis are limited by viscous dissipation in the cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Adhesion↗
PubMed1989

The distribution of lipids and sterols in cell types from the marine sponge Pseudaxinyssa sp.

The sponge Pseudaxinyssa sp., unique in sterol and fatty acid composition, was cellularly dissected into fractions enriched in each of the major cell types present in the sponge: microbial symbionts (cyanobacteria), small sponge cells (pinacocytes and choanocytes), and large sponge cells (archeocytes and cyanophytes). Three phototrophic microbial symbionts were also isolated from the cell fractions and grown in culture. An unsymmetrical distribution of fatty acids and sterols was observed for the sponge cells: small cells contained larger quantities of long chain fatty acids (greater than C24) and smaller quantities of sterols than were present in the larger sponge cells. Moreover, the rare sterols 24-isopropylcholesterol predominated in the smaller sponge cells, whereas its 22-dehydro analog predominated in the larger sponge cells. Long chain fatty acids and sterols were not detected in the cultured microbial symbionts. This constitutes the first report of lipid variability according to cell type for this most primitive group of Metazoa.

Animals↗
PubMed1989

Cortical shell-liquid core model for passive flow of liquid-like spherical cells into micropipets.

Many nonadherent cells exist as spheres in suspension and when sucked into pipets, deform continuously like liquids within the fixed surface area limitation of a plasma membrane envelope. After release, these cells eventually recover their spherical form. Consequently, pipet aspiration test provides a useful method to assay the apparent viscosity of such cells. For this purpose, we have analyzed the inertialess flow of a liquid-like model cell into a tube at constant suction pressure. The cell is modeled as a uniform liquid core encapsulated by a distinct cortical shell. The method of analysis employs a variational approach that minimizes errors in boundary conditions defined by the equations of motion for the cortical shell where the trial functions are exact solutions for the flow field inside the liquid core. For the particular case of an anisotropic liquid cortex with persistent tension, we have determined universal predictions for flow rate scaled by the ratio of excess pressure (above the threshold established by the cortical tension) and core viscosity which is the reciprocal of the dynamic resistance to entry. The results depend on pipet to cell size ratio and a parameter that characterizes the ratio of viscous flow resistance in the cortex to that inside the cytoplasmic core. The rate of entry increases markedly as the pipet size approaches the outer segment diameter of the cell. Viscous dissipation in the cortex strongly influences the entry flow resistance for small tube sizes but has little effect for large tubes. This indicates that with sufficient experimental resolution, measurement of cell entry flow with different-size pipets could establish both the cortex to cell dissipation ratio as well as the apparent viscosity of the cytoplasmic core.

Cell Adhesion↗
PubMed1989

Apparent viscosity and cortical tension of blood granulocytes determined by micropipet aspiration.

Continuous deformation and entry flow of single blood granulocytes into small caliber micropipets at various suction pressures have been studied to determine an apparent viscosity for the cell contents and to estimate the extent that dissipation in a cortical layer adjacent to the cell surface contributes to the total viscous flow resistance. Experiments were carried out with a wide range of pipet sizes (2.0-7.5 microns) and suction pressures (10(2)-10(4) dyn/cm2) to examine the details of the entry flow. The results show that the outer cortex of the cell maintains a small persistent tension of approximately 0.035 dyn/cm. The tension creates a threshold pressure below which the cell will not enter the pipet. The superficial plasma membrane of these cells appears to establish an upper limit to surface dilation which is reached after microscopic "ruffles" and "folds" have been pulled smooth. With aspiration of cells by small pipets (less than 2.7 microns), the limit to surface expansion was derived from the maximal extension of the cell into the pipet; final areas were measured to be 2.1 to 2.2 times the area of the initial spherical shape. For suctions in excess of a threshold, the response to constant pressure was continuous flow in proportion to excess pressure above the threshold with only a small nonlinearity over time until the cell completely entered the pipet (for pipet calibers greater than 2.7 microns). With a theoretical model introduced in a companion paper, (Yeung, A., and E. Evans., 1989, Biophys. J. 56:139-149) the entry flow response versus pipet size and suction pressure was analyzed to estimate the apparent viscosity of the cell interior and the ratio of cortical flow resistance to flow resistance from the cell interior. The apparent viscosity was found to depend strongly on temperature with values on the order of 2 x 10(3) poise at 23 degrees C, lower values of 1 x 10(3) poise at 37 degrees C, but extremely large values in excess of 10(4) poise below 10 degrees C. Because of scatter in cell response, it was not possible to accurately establish the characteristic ratio for flow resistance in the cortex to that inside the cell; however, the data showed that the cortex does not contribute significantly to the total flow resistance.

Granulocytes↗
PubMed1989

Rheological and adherence properties of sickle cells. Potential contribution to hematologic manifestations of the disease.

Hematologic manifestations of sickle cell disease are varied and complex, and there is also a great variation in these manifestations among different individuals with the disease. While substantial efforts have been invested in defining the cellular basis for these clinical manifestations--including the evaluation of the potential contributions of intracellular polymer content, kinetics of hemoglobin polymerization, rheological abnormalities, oxidant membrane damage, and adherence of sickle cells to vascular endothelial cells--we are still far from understanding the relative contributions of each of these factors to varied manifestations of the disease. While the data discussed in this paper raise interesting issues regarding the potential contribution of rheological and adherence properties of sickle cells to altered flow dynamics in the microvasculature, they fall short of defining the direct contributions of these factors to various clinical manifestations. Further detailed characterization of various cellular abnormalities of sickle cells and how each of these factors acting alone or in combination with other cellular and extracellular factors such as microvasculature changes contribute to different clinical manifestations will be needed to further our understanding of the pathophysiology of this complex disorder.

Anemia, Sickle Cell↗
PubMed1987

Induction of fibrinogen and a subset of acute phase response genes involves a novel monokine which is mimicked by phorbol esters.

We have investigated the requirements for the induction of the acute phase response to inflammation using the FAZA rat hepatocyte cell line which can be induced to activate the acute phase response genes with supernatants from human or rat monocytes. Using ribonuclease mapping of fibrinogen transcripts, we find that the tumor promoter 12-O-tetradecanoylphorbol-13-acetate can induce a 10-20-fold increase in properly initiated and spliced fibrinogen mRNA. This response is likely to be mediated by protein kinase C (Ca2+/phospholipid-dependent enzyme) since the synthetic diacylglycerol, 1-oleoyl-2-acetylglycerol, can also induce fibrinogen mRNA. In addition to the alpha, beta, and gamma chains of fibrinogen, other acute phase response mRNAs are induced by 12-O-tetradecanoylphorbol-13-acetate including alpha 2-macroglobulin. The active agent capable of inducing the fibrinogen mRNAs in the monocyte supernatants is clearly not interleukin 1 (IL-1) or tumor necrosis factor. The FAZA cell line does not have detectable IL-1 receptors and does not respond to either murine or human IL-1 or the 30-kDa precursor for IL-1. In addition, fibrinogen cannot be induced by tumor necrosis factor alpha in this cell line, and the active agent in monocytes supernatants cannot be neutralized with polyclonal or monoclonal antibodies to tumor necrosis factor alpha. We conclude that a third as yet uncharacterized agent is responsible for the induction of fibrinogen during the acute phase response and that this agent transduces its signal to the fibrinogen genes by a mechanism involving protein kinase C.

Acute-Phase Proteins↗