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Biomedical subjects

I Newman

Publications and source records attributed to I Newman.

At least 19 recordsLinked to original sources
PubMed2001

Measurements of net fluxes and extracellular changes of H+, Ca2+, K+, and NH4+ in Escherichia coli using ion-selective microelectrodes.

This study introduced the use of a non-invasive ion-selective microelectrode (MIFE) technique to study membrane-transport processes in bacteria. Net ion fluxes and changes in the extracellular concentrations of H+, Ca2+, K+ and NH4+ in adherent bacteria, isolated from cultures at different growth stages (exponential, late exponential, and stationary phases), were monitored. With the exception of Ca2+, a significant (P=0.05) difference was found in the magnitude of net fluxes of the ions measured from bacterial cells at different stages of the population growth curve. The magnitude of the H+ response was glucose-dependent with maximum changes occurring at the highest concentration. There was a progressive increase in H+ extrusion followed by a gradual return to zero at late stationary phase. Measurements of net ion fluxes crossing the bacterial cytoplasmic membrane, demonstrated here for the first time, may offer insight into underlying mechanisms of ion transport kinetics. Applications of the non-invasive ion-selective microelectrode technique in microbiology are discussed.

Calcium↗
PubMed2000

Pilot study of the cyclic fatigue characteristics of five endodontic posts with four core materials.

This pilot study concerned the cyclic fatigue of five different endodontic post systems (AccessPost(R), Flexi-Flange(R), Flexi-Post(R), ParaPost(R), and Vlock(R)) with four different core materials (Tytin(R) Silver amalgam, Ti-Core(R), Ketac-Silver(R) and G-C Miracle Mix(R)). In vitro cyclic fatigue was performed using a fatigue machine that simulates masticatory fatigue forces. An instantaneous force of 5 lb was applied to each post and core combination for a test configuration of 4 000 000 repetitions or until failure occurred. The type of failure and number of repetitions at failure was recorded for each sample tested. Two-way ANOVA was used to compare groups. All posts/core samples with Ti-Core and Tytin Silver amalgam completed the test configuration of 4 000 000 cycles without failures. All posts/core samples with Ketac-Silver failed before the 4 000 000 test cycle configuration, all as a result of core failures. All posts/core samples with G-C Miracle Mix failed in a similar way. The Newman-Keuls multiple comparison test illustrated that Ti-Core and Tytin Silver amalgam were similar to each other and were superior to both G-C Miracle Mix and Ketac-Silver. Similar fatigue test results are found in the literature.

Bicuspid↗
PubMed2000

Retention of a core material supported by three post head designs.

STATEMENT OF PROBLEM: There are few studies on the retention of core build-up materials to prefabricated post head designs, especially for a new ceramic post design. PURPOSE: This in vitro study compared the retention of 2 types of core build-up materials (Ti-Core titanium-reinforced composite and a GC Miracle Mix silver-reinforced glass ionomer) supported by 3 post head designs (Flexi-Post, AccessPost, and Cerapost dowel). For all test groups, heads of the posts were placed into the core material at a 90-degree angle to the surface. Test specimens (unloaded) were then placed into a special jig and retention test was performed using an 810 MTS testing machine. MATERIAL AND METHODS: This study consisted of 6 groups with 10 specimens per group. A 3 x 2 factorial design was used to test for statistical significance and results were considered significant when P <.05. RESULTS: Results of the retention test were as follows: group 1, Flexi-Post/Ti-Core 220.0 lb (982.1 N), group 2, AccessPost/Ti-Core 212.7 lb (949.6 N), group 3, Cerapost/Ti-Core 41. 8 lb (186.6 N), group 4, Flexi-Post/Miracle Mix 43.4 lb (193.8 N), group 5, AccessPost/Miracle Mix 61.6 lb (275 N), and group 6, Cerapost/Miracle Mix 7.5 lb (33.5 N). Results of the ANOVA revealed a highly significant difference between posts and cores (P <.0001). CONCLUSION: Post head designs of the stainless steel AccessPost and Flexi-Post dowels offers greater retention then the smooth ceramic head design of the Cerapost dowel. In addition, the composite core material (Ti-Core) offers greater retentive strength values than the glass ionomer material (Miracle Mix).

Analysis of Variance↗
PubMed2000

Ion-specific mechanisms of osmoregulation in bean mesophyll cells.

Transient kinetics of net H+, K+, Ca2+, and Cl- fluxes were measured non-invasively, using an ion-selective microelectrode technique, for bean (Vicia faba L.) leaf mesophyll in response to 150 mM mannitol treatment. In a parallel set of experiments, changes in the plasma membrane potential and the total proline content in leaves were monitored. Regardless of the ionic composition of the bath solution, hyperosmotic stress caused a significant increase in the K+ and Cl- uptake into mesophyll cells. At the same time, no significant proline changes were observed for at least 16 h after the onset of stress. Experiments with inhibitors suggested that potassium inward rectifier (KIR) channels, exhibiting mechanosensitive properties and acting as primary receptors of osmotic stress, are likely to be involved. Due to the coupling by membrane potential, changes in K+ and Cl- transport may modify activity of the plasma membrane H+-pump. Such coupling may also be responsible for the mannitol-induced oscillations (period of about 4 min) in net ion fluxes observed in 90% of plants. Calculations show that influx of K+ and Cl- observed in response to hyperosmotic treatment may provide an adequate osmotic adjustment in bean mesophyll, which suggests that the activity of the plasma membrane transporters for these ions should be targeted to improve osmotolerance, at least in this crop.

Calcium↗
PubMed1999

Effects of three bonding systems on the torsional resistance of titanium-reinforced composite cores supported by two post designs.

STATEMENT OF PROBLEM: There are no studies that have investigated the effects of bonding agents on the resistance to torque of a composite core supported by a prefabricated post. PURPOSE: This study investigated the ability of bonding agents to resist rational forces applied to titanium-reinforced composite cores supported by 2 post designs. MATERIAL AND METHODS: Two post designs (AccessPost and ParaPost dowels) with titanium-reinforced core material and 4 bonding conditions (AllBond-2, ScotchBond Multi-Purpose, Tenure A&B, and without a bonding agent) were studied. A total of 80 specimens in 8 experimental groups were prepared and subjected to clockwise torsional forces until failure. RESULTS: Torsional values ranged from 53.31 in. x oz (ParaPost/ScotchBond Multi-Purpose) to 72.31 in. x oz (AccessPost/ScotchBond Multi-Purpose). Two-way of analysis of variance failed to demonstrate a significant difference among posts or type of bonding system. CONCLUSION: The use of a multistep bonding agent had no significant effect on the torsional resistance of a core supported by a passive endodontic post.

Acid Etching, Dental↗
PubMed1999

Light-induced changes in hydrogen, calcium, potassium, and chloride ion fluxes and concentrations from the mesophyll and epidermal tissues of bean leaves. Understanding the ionic basis of light-induced bioelectrogenesis

Noninvasive, ion-selective vibrating microelectrodes were used to measure the kinetics of H+, Ca2+, K+, and Cl- fluxes and the changes in their concentrations caused by illumination near the mesophyll and attached epidermis of bean (Vicia faba L.). These flux measurements were related to light-induced changes in the plasma membrane potential. The influx of Ca2+ was the main depolarizing agent in electrical responses to light in the mesophyll. Changes in the net fluxes of H+, K+, and Cl- occurred only after a significant delay of about 2 min, whereas light-stimulated influx of Ca2+ began within the time resolution of our measurements (5 s). In the absence of H+ flux, light caused an initial quick rise of external pH near the mesophyll and epidermal tissues. In the mesophyll this fast alkalinization was followed by slower, oscillatory pH changes (5-15 min); in the epidermis the external pH increased steadily and reached a plateau 3 min later. We explain the initial alkalinization of the medium as a result of CO2 uptake by photosynthesizing tissue, whereas activation of the plasma membrane H+ pump occurred 1.5 to 2 min later. The epidermal layer seems to be a substantial barrier for ion fluxes but not for CO2 diffusion into the leaf.

Journal Article↗
PubMed1998

Retention of three endodontic posts cemented with five dental cements.

STATEMENT OF PROBLEM: The retention of a post is believed to be a major factor in restoration survival. Therefore the cement with the greatest in vitro retention property should give the best performance for a restoration. PURPOSE: This study compared retentive values of three posts (Flexi-Post, AccessPost, and ParaPost) cemented with five cements (Flexi-Flow, zinc phosphate, Advance, Duet, and Ketac-Cem) plus a control group that consisted of a Flexi-Post No. 2 dowel without cement. MATERIAL AND METHODS: A total of 160 recently extracted human single-rooted teeth with crowns removed at the cementoenamel junction were divided into 16 groups of 10 samples. Post holes were prepared according to manufacturers' instructions. Posts were then cemented with one of the five cements. Each sample was placed into a specialized jig and on a tensile testing machine with crosshead speed of 0.638 cm/minute, applied until failure. A two-way analysis of variance and Newman-Keuls multiple range comparison tests were performed for all cemented groups. A one-way analysis of variance and a Student-Newman-Keuls multiple range comparison test were performed only for the groups with the Flexi-Post dowel, this included the no cement condition, with significant results if p < 0.05. RESULTS: Flexi-Post dowel with Flexi-Flow Natural cement obtained the highest retentive value (303.91 pounds). ParaPost dowel with Duet cement exhibited the lowest retention value (21.23 pounds). The Flexi-Post dowel demonstrated higher mean retention than AccessPost or ParaPost dowels, AccessPost dowel was higher than ParaPost dowel. Flexi-Flow cement had the highest overall mean retention followed, in decreasing order, by zinc phosphate, Advance, Ketac-Cem, and Duet cements. CONCLUSIONS: Flexi-Post dowel was the most retentive post studied with values ranging from 303.91 pounds with Flexi-Flow Natural cements to 150.93 pounds without cement. Flexi-Flow cements had a higher overall mean retention than other cements studied.

Analysis of Variance↗
PubMed1997

Cyclic fatigue testing of five endodontic post designs supported by four core materials.

PURPOSE: This pilot study examined the cyclic fatigue of five endodontic post systems (AccessPost, Flexi-Flange, Flexi-Post, ParaPost, and Vlock) with four core materials (Tytin silver amalgam, Ti-Core, Ketac-Silver and G-C Miracle Mix). MATERIAL AND METHODS: In vitro cyclic fatigue was performed with a machine designed to simulate masticatory fatigue forces. An instantaneous force of 22.2 N (5 pounds) was applied to each post and core combination for a test configuration of 4,000,000 repetitions, or until failure occurred. The type of failure and number of repetitions at failure was recorded for each sample tested. Two-way analysis of variance (ANOVA) was used to compare groups. RESULTS: All posts/core samples with Ti-Core composite and Tytin silver amalgam completed the test with no failures. All posts/core samples with Ketac-Silver material failed before the 4,000,000 test cycle configuration and all failures were core failures. All posts/core samples with G-C Miracle Mix material failed in a similar manner. Newman-Keuls multiple comparison test illustrated that, with this simulated fatigue test, Ti-Core material and Tytin silver amalgam were superior to both G-C Miracle Mix and Ketac-Silver materials.

Analysis of Variance↗
PubMed1997

Locomotion and chemotaxis of lymphocytes.

The behaviour of locomotor T and B lymphocytes and the chemoattractants to which they respond in vitro are reviewed. Following activation, T cells respond by locomotion and chemotaxis to cytokine attractants including IL-15 and IL-2 and several chemokines. In activated B cells chemotaxis may be signalled through the antigen receptor. Conversely resting lymphocytes respond poorly to the above signals though their locomotion is activated by contact with high endothelial venular cells. These differences in locomotion between resting and activated lymphocytes, together with differences in adhesion, may explain why activated lymphocytes migrate preferentially into inflammatory sites while resting cells recirculate.

Animals↗
PubMed1996

The bacterial superantigen Staphylococcal enterotoxin B stimulates lymphocyte locomotor capacity during culture in vitro.

The bacterial superantigen Staphylococcal enterotoxin B (SEB) was investigated for its effects on lymphocyte locomotion in vitro. Culture of peripheral blood mononuclear cells (PBMC) for 24-72 hr in SEB (1-100 micrograms/ml) increased the proportion of lymphocytes in locomotor (polarized) morphology and capable of invading collagen gels, to the same extent as the established locomotor activator, anti-CD3 (alpha-CD3), though the conventional antigen, tetanus toxoid was ineffective. The cells responding to SEB were predominantly T cells. SEB had no effect on lymphocyte locomotion in short-term (45 min) assays, thus its effect is to stimulate growth-related locomotor capacity and it does not act as a chemoattractant. During culture of PBMC in SEB, the chemokines interleukin-8 (IL-8) and macrophage chemotactic protein-1 (MCP-1) were released into the culture medium. The presence of anti-IL-8, but not of anti-MCP-1, either during culture or added to SEB culture supernatants and tested in short-term assays, inhibited the development of polarization suggesting that IL-8, which is a lymphocyte chemoattractant, also plays a key role in SEB-induced locomotor activation. Among SEB-activated lymphocytes, CD45RO+CD45RA- lymphocytes showed enhanced locomotor responses, but a relation was not found between locomotor activity and the presence of cell surface CD69.

Cell Movement↗
PubMed1996

Comparison of the fractural strength for three combination cast post systems.

This study compared the fractural strength measured on a 45 degree angle for three combination cast post systems (Parapost, ExactaCast and Luminex 2000). A force applied at a 45 degree angle on the bench was used to simulate the clinical situation. Many similar studies are found in literature. The experiment was divided into three groups made up of 10 samples each. Castings were fabricated in semi-precious metal from: Parapost burnout post / Duralay patterns (group 1), ExactaCast / a new butyl methacrylate acrylic (AccuSet) patterns (group 2) and Luminex 2000 / Lumin-X light cured gel patterns (group 3). The fractural strength [tests] were performed using a MTS testing machine and failure was measure in pounds. Statistical analysis including a student's test were performed to ensure complete significance between groups. The ExactaCast system had the highest mean (283.9 pounds), while the Luminex 2000 system had the lowest (255.1 pounds). There was no statistical difference in the fractural strength for all three groups studied. It seemed that the fractural strength of tooth structure represents the highest level of failure obtained regarding this experimental test constraint.

Bicuspid↗
PubMed1994

Chemoattractant activity of IL-2 for human lymphocytes: a requirement for the IL-2 receptor beta-chain.

Recombinant human interleukin-2 (IL-2) stimulated locomotion and chemotaxis of human blood lymphocytes as measured by shape change to a polar morphology, by orientation in a chemotactic gradient, and by a collagen gel invasion assays. IL-2 stimulated locomotion of a larger number of lymphocytes than IL-8 or macrophage inflammatory protein (MIP)-1 alpha, but the maximally effective concentration of all three was similar (around 100 ng/ml). Activation of the lymphocytes by culture for 24-48 hr in fetal calf serum (FCS), anti-CD3, or purified protein derivative (PPD) increased the proportion of responsive cells, though even direct from blood, > 20% of lymphocytes showed locomotor responses to IL-2, a figure which was similar to the number of IL-2 receptor (IL-2R) beta+ lymphocytes but higher than the number of IL-2R alpha+ cells. The effect of antibodies to IL-2R alpha and IL-2R beta as inhibitors of these responses was therefore tested. Anti-IL-2R beta (alpha IL-2R beta) completely inhibited the response of both resting and activated cells: alpha IL-2R alpha had no inhibitory effect on the locomotion of lymphocytes direct from blood, and only partially inhibited locomotion after culture for 48 hr in alpha CD3 or PPD. The locomotor response to IL-2 was inhibited by pretreatment of the cells with herbimycin, a protein tyrosine kinase (PTK) inhibitor, an observation consistent with PTK control of cytoskeletal activity following binding of IL-2 to IL-2R beta. These results suggest that the beta-chain of the IL-2R is required for activation of lymphocyte locomotion by IL-2 and that binding of IL-2 to this chain alone is sufficient for a response.

Benzoquinones↗
PubMed1993

Locomotor responses of human CD45 lymphocyte subsets: preferential locomotion of CD45RO+ lymphocytes in response to attractants and mitogens.

The CD45RO+ population of lymphocytes from human blood contains a higher proportion of locomotor cells than the CD45RA+ population. Direct from blood there were few locomotor lymphocytes (< 15%), but, among these, a higher proportion of CD45RO+ than of CD45RA+ cells responded to the chemotactic stimuli, foetal calf serum (FCS) and interleukin-2 (IL-2) in polarization assays. Likewise, after overnight culture, a higher proportion of CD45RO+ cells responded to IL-8. Culture for 24-72 hr in activators such as anti-CD3, purified protein derivative (PPD), phytohaemagglutinin (PHA), concanavalin A (Con A), pokeweed mitogen (PWM) or in an allogeneic mixed leucocyte reaction (AMLR) increased the proportion of locomotor lymphocytes to 20-60%, and the CD45RO+ subset showed proportionately more polarized cells than the CD45RA+ subset after culture with all the above activators. Preferential migration of CD45RO+ cells into collagen gels was also seen after culture in antigenic stimuli (PPD or AMLR) but not with polyclonal activators (alpha CD3 or Con A). Double labelling showed that, within the CD4+ and CD8+ subsets, antigen-stimulated CD45RO+ T cells invaded collagen gels in higher proportions than CD45RA+ T cells. Clustering of lymphocytes with accessory cells is an essential prerequisite for locomotion and, after culture in alpha CD3, CD45RO+ lymphocytes were found preferentially in clusters with monocytes. In all of the above populations, CD45RO+ lymphocytes were larger in size. These findings suggest that, not only selective adhesion to vascular endothelium as reported earlier, but also selective locomotion recruits CD45RO+ lymphocytes into sites of inflammation.

Cell Aggregation↗
PubMed1992

Identification of IL-8 as a locomotor attractant for activated human lymphocytes in mononuclear cell cultures with anti-CD3 or purified protein derivative of Mycobacterium tuberculosis.

On culture of human blood mononuclear cells for 24 to 48 h with anti-CD3 (aCD3) or purified protein derivative of Mycobacterium tuberculosis, chemoattractants are released into the medium which induce polarization and locomotion of activated (G1) lymphocytes but not resting lymphocytes. Here we show that, during a period of up to 72 h of culture, IL-8 is released in nanomolar quantities into the supernatant and that the lymphocyte chemoattractant activity of these supernatants is inhibited by incubation with anti-IL-8. Examination of the cultured mononuclear cells by immunofluorescence suggests that many monocytes, but almost no lymphocytes in aCD3 cultures contain IL-8 in cytoplasmic organelles, yet few monocytes direct from blood stained for IL-8. IL-8 is an attractant for only a small proportion (ca 10%) of lymphocytes direct from blood. The proportion of responding cells is increased after culture for 24 to 48 h in aCD3 or purified protein derivative of Mycobacterium tuberculosis, and these are a phenotypically distinct subpopulation consisting of large lymphocytes enriched for CD45RO. These cells respond to their own culture supernatants and to IL-8 in polarization assays and by invasion of collagen gels into which the attractants are incorporated. They also show orientation to a source of IL-8 in a chemotactic gradient. These responses are consistent with in vivo observations that the lymphocytes which migrate selectively into inflammatory sites are activated. The fact that many lymphocytes do not respond to IL-8 may reflect the diversity of migratory pathways shown by lymphocytes in vivo, the locomotion of small, recirculating, lymphocytes being regulated by other, unknown, locomotor stimuli.

Animals↗
PubMed1992

Methods for phenotyping polarized and locomotor human lymphocytes.

Lymphocytes show heterogeneity both in phenotype and in locomotor activity; methods which permit the simultaneous assessment of both are therefore useful. The activation of locomotion may be dependent on interactions between lymphocytes and accessory cells, making it necessary to study mixed cell populations. We describe here two in vitro procedures which do this. Firstly the lymphocyte polarization assay has been adapted by using the alkaline phosphatase-anti-alkaline phosphatase method (APAAP) after fixation with glutaraldehyde. Secondly, we have allowed lymphocytes to invade collagen gels and then digested the gel with collagenase to recover the locomotor population. This can then be phenotyped by immunofluorescence using a fluorescence-activated cell sorter (FACS). Collagenase did not affect the staining pattern with commonly-used markers such as CD3, -4, -8, -19, -29, -45RO and -45RA.

Alkaline Phosphatase↗
PubMed1991

Human leucocyte migration through collagen matrices containing other extracellular matrix components.

The purpose of this study was to investigate the migration of human peripheral blood leucocytes through collagen gels containing extracellular matrix components in vitro. This further extends the findings of a previous study (Reid et al, 1990), using rabbit peritoneal neutrophils, in which it was found that increasing the mechanical strength of the gels decreased the cell migration. In the current study it was found that human neutrophil and lymphocyte migration through collagen matrices was inhibited by increasing the collagen concentration, whereas the presence of serum had no effect on migration. Incorporation of chondroitin sulphate into collagen gel matrices resulted in a slight increase in leucocyte migration. The presence of elastin had no effect on the migration of leucocytes through collagen matrices, whereas incorporation of hyaluronate into collagen matrices decreased leucocyte migration. The morphology of these matrices suggests that altered migration was not due to differences in pore size between fibres.

Cell Movement↗
PubMed1989

Chemotactic activity of lymphotoxin and tumour necrosis factor alpha for human neutrophils.

Lymphotoxin (TNF beta) and tumour necrosis factor alpha (TNF alpha) stimulate locomotion and chemotaxis of human blood neutrophils as measured in three assays. Both cytokines stimulate morphological polarization of neutrophils in suspension; both stimulate locomotion of neutrophils into micropore filters; both cause orientation of neutrophils towards a gradient source. Orientation in a gradient suggests a chemotactic effect. The action of both cytokines is similar but is not as strong as that of formyl peptide used as a positive control. Myelomonocytic cell lines (U937 and HL-60) develop responsiveness to formyl peptides on maturation but not to TNF alpha or beta.

Chemotaxis, Leukocyte↗