Biomedical subjects

R J Gilbert

Publications and source records attributed to R J Gilbert.

At least 19 recordsLinked to original sources

PubMed1995

Respiratory phase resetting and airflow changes induced by swallowing in humans.

1. Relationships between the timing of respiration and deglutition were studied in thirty awake healthy subjects at rest. Deglutition was monitored by submental electromyography, pharyngeal manometry and videofluoroscopy. Respiration was recorded by measurement of oronasal airflow and chest wall movement. Three types of deglutition were studied: injected bolus swallows, spontaneous swallows, and visually cued swallows of boluses previously placed in the mouth. 2. The effect of each swallow on respiratory rhythm was characterized by measurement of cophase, defined as the interval between the onset of deglutitive submental EMG activity to the onset of subsequent rescheduled inspirations. Cophase was determined for swallows initiated at different phases of the respiratory cycle. In all subjects deglutition caused phase resetting of respiratory rhythm. Cophase was largest for swallows initiated near the the inspiratory-expiratory (E-I) transition and smallest for swallows initiated near the expiratory-inspiratory (E-I) transition. The pattern of respiratory resetting by deglutition was topologically classified as type 0. This pattern was shown for swallows induced by bolus injection or visual cue, and for spontaneous swallows. 3. The incidence of spontaneous deglutition was influenced by the position of the swallow in the respiratory cycle. Few spontaneous swallows were initiated near the E-I transition whereas most occurred from late inspiration to mid-expiration. 4. Deglutition caused an abrupt decrease in airflow leading to an interval of apnoea, followed by a period of expiration. The duration of deglutition apnoea for spontaneous swallows was shorter than that for 5 ml bolus swallows, and was unaffected by the respiratory phase of swallow initiation. The period of expiration after swallowing was longest for swallows initiated at the I-E transition, and shortest for E-I swallows. 5. The intervals between bolus injection and the onset of deglutition apnoea, and the timing of swallowing events, were not significantly altered by the phase in the respiratory cycle at which swallowing was exhibited. 6. To quantify the relationship between bolus flow and respiration, we determined the latencies between cessation of inspiratory airflow and arrival of the bolus at the larynx (alpha), and between laryngeal bolus departure and resumption of inspiratory airflow (delta). Both values were dependent upon the respiratory phase of swallowing. The lowest values for alpha and delta were found for early-inspiratory and late-expiratory swallows, respectively. 7. We conclude that swallowing causes respiratory phase resetting with a pattern that is characteristic of the strong perturbations of an attractor-cycle oscillator.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1995

Dynamic magnetic resonance imaging of vocal cord closure during deglutition.

BACKGROUND & AIMS: Vocal cord closure is instrumental in airway protection during deglutition. Conventional imaging of vocal cord closure and reopening during deglutition requires invasive and nonphysiological methods. The aim of this study was to characterize the biomechanical properties of normal vocal cord adduction/abduction during deglutition using echoplanar magnetic resonance imaging, a technique that has the capability of imaging soft-tissue motion with real-time temporal resolution. METHODS: The movements of laryngeal and vocal cord structures during swallowing were determined in 11 normal volunteers by single slice and axially reformatted multislice coronal echoplanar images. RESULTS: During swallowing, the larynx ascended to peak elevation, maintained peak elevation for a discrete interval, and descended to its resting position. Vocal cord adduction occurred with a symmetric tent-like configuration at the midpoint of maximal laryngeal elevation, whereas vocal cord abduction occurred at the midpoint of laryngeal descent. Spatial analysis of vocal cord configuration during adduction determined that the vocal cords attained an initial parallel configuration during ascent, followed by closure at peak laryngeal elevation. CONCLUSIONS: These results show that the vocal cords adduct and abduct synchronously with laryngeal ascent and descent, respectively, during deglutition. Echoplanar magnetic resonance imaging constitutes a novel tool used to assess clinical abnormalities of deglutitive laryngeal function.

Adult↗

PubMed1995

Salmonella enteritidis phage type 4 isolates more tolerant of heat, acid, or hydrogen peroxide also survive longer on surfaces.

In a comparative study of different Salmonella enteritidis phage type 4 isolates we found that those isolates with enhanced heat tolerance also survived better than isolates that were heat sensitive either at pH 2.6, in 10 mM H2O2, or on surfaces. Culture to the stationary phase increased the heat tolerance of all isolates and the acid and H2O2 tolerance of heat-tolerant isolates. With heat-sensitive isolates, however, extended culture had no impact on survival in H2O2 and only a marginal impact on acid tolerance. The growth phase had no appreciable impact on the surface survival of any of the isolates.

Animals↗

PubMed1995

Involvement of Ras-related Rho proteins in the mechanisms of action of Clostridium difficile toxin A and toxin B.

Toxins A and B of Clostridium difficile are responsible for pseudomembranous colitis, a disease that afflicts a substantial number of hospitalized patients treated with antibiotics. A major effect of these proteins is the disruption of the actin cytoskeleton. Recently, I. Just, G. Fritz, K. Aktories, M. Giry, M. R. Popoff, P. Boquet, S. Hegenbarth, and C. von Eichel-Streiber (J. Biol. Chem. 269:10706-10712, 1994) implicated Rho proteins as cellular targets of C. difficile toxin B, since pretreatment of cells or purified Rho with toxin prevented subsequent ADP-ribosylation of Rho by exoenzyme C3. Moreover, they showed that overexpression of Rho proteins in cells suppressed cell rounding normally associated with exposure of cells to C. difficile toxin B. Here we expand these findings by showing directly that Rho proteins are covalently modified by both C. difficile toxins A and B. In addition, we demonstrate that the stability of toxin-modified Rho in NIH 3T3 cells is dramatically reduced. Finally, we show that C. difficile toxins A and B do not have similar effects on the closely related Rac and CDC42 GTP-binding proteins.

3T3 Cells↗

PubMed1995

Clostridium difficile toxin B activates calcium influx required for actin disassembly during cytotoxicity.

The principal cellular response to Clostridium difficile toxin B, a protein toxin associated with antibiotic-associated colitis, is the disassembly of actin microfilaments. Although receptor-activated signal transduction mechanisms have been proposed to mediate these effects, the intracellular events that precede actin breakdown are unknown. In NIH-3T3 fibroblasts, toxin B induced an elevation of intracellular calcium possessing either a slow (minutes) or fast (seconds) rise time, followed by a sustained elevation of calcium concentration. Subcellular analysis of steady-state calcium distribution after toxin B demonstrated that the increase of calcium was homogeneous throughout the cytosol and did not vary based on the kinetics of the initial calcium rise. All calcium responses were blocked by substitution with calcium-free buffer or buffer containing lanthanum chloride, indicating that the rise in calcium was attributable to calcium influx from the extracellular space. Quantitatively similar responses were observed in primary cultured gastric smooth muscle and AR42J pancreatic tumor cells, suggesting that toxin-induced calcium signal transduction was conserved between cell types. The morphological response to toxin B consisted of sequential dissociation of the actin cytoskeleton from membrane attachments, retraction of actin stress fibers from the periphery to the perinuclear region, loss of fibre alignment, and cell rounding. The actin reorganization associated with toxin B was blocked by incubation of cells in calcium-free media or the clamping of intracellular calcium with cell-permeant calcium chelating agents. These results demonstrate that the calcium influx activated by C. difficile toxin B is a necessary condition for the breakdown of filamentous actin associated with cytotoxicity.

3T3 Cells↗

PubMed1994

Substitution of arginine 719 for glutamic acid in human plasminogen substantially reduces its affinity for streptokinase.

In isolation human plasminogen possesses no enzymatic activity, yet upon formation of an equimolar complex with the bacterial protein streptokinase, it acquires a plasminogen activator function. The region(s) of plasminogen and of streptokinase which mediate complex formation has (have) not been previously published. Here it is reported that a single-residue substitution (Arg719-->Glu) in the serine protease domain of full-length Glu-plasminogen substantially reduces its affinity for streptokinase. The plasminogen variant displays no other significant differences from the wild-type molecule with respect to activation by two-chain urokinase-type plasminogen activator, recognition by monoclonal antibodies, or ability to undergo conformational change. It is concluded that Arg719 in human plasminogen is an important determinant of the streptokinase binding site, although further sites are likely to contribute both to the affinity of plasminogen for streptokinase and to mechanisms by which the active site is formed within the complex.

Animals↗

PubMed1994

Retrospective analysis of a secondary structure prediction: the catalytic domain of matrix metalloproteinases.

Secondary structure prediction of the catalytic domain of matrix metalloproteinases is evaluated in the light of recently published experimentally determined structures. The prediction was made by combining conformational propensity, surface probability, and residue conservation calculated for an alignment of 19 sequences. The position of each observed secondary structure element was correctly predicted with a high degree of accuracy, with a single beta-strand falsely predicted. The domain fold was also anticipated from the prediction by analogy with the structural elements found in the distantly related metalloproteinases thermolysin, astacin, and adamalysin.

Animals↗

PubMed1994

Calcium efflux from an intracellular pool activated by GTP hydrolysis in cultured gastric smooth muscle.

In these studies, we have characterized calcium movement due to guanosine triphosphate (GTP) hydrolysis from an ATP-sequestered intracellular calcium pool in cultured gastric smooth muscle. GTP (1-100 microM), when added to an ATP-regenerating medium, resulted in a concentration-dependent and irreversible efflux of calcium from an organellar calcium pool. GTP-induced calcium efflux was not affected by variation of the ATP/ADP ratio (8.5-155.0), indicating that GTP did not act by inhibiting calcium influx via calcium adenosinetriphosphatase. To assess whether the calcium increase was necessarily associated with GTP hydrolysis, experiments were performed with the nonhydrolyzable guanine nucleotide analogues guanosine 5'-[beta-thio]diphosphate (GDP beta S), 5'-guanylyl imidodiphosphate guanosine (GppNHp), and 5'-O-(3-thiotriphosphate) (GTP gamma S). Administration of GDP beta S and GppNHp resulted in no significant calcium efflux. GTP gamma S caused a small steady-state calcium increase (20% of that induced by the hydrolyzable nucleotide) but irreversibly inhibited all subsequent calcium increase due to GTP. The possibility that GTP may either modify the concentration of mobilizable calcium in inositol trisphosphate (IP3)-sensitive calcium stores or the responsivity of IP3-associated calcium channels was assessed by two experiments: 1) prior administration of GTP at concentrations < or = 100 microM had no effect on IP3-induced calcium release, and 2) heparin, which competitively inhibits IP3 binding to its receptor on the endoplasmic reticulum, did not affect GTP-associated calcium increase. These results demonstrate that, in gastric smooth muscle, GTP causes calcium efflux from an intracellular pool that is functionally independent from that pool sensitive to IP3.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗

PubMed1993

Quantitative relationship between liquid bolus flow and laryngeal closure during deglutition.

We employed digital image analysis to assess the relative movements of the hyoid, larynx, and bolus as a function of liquid bolus volume (2-15 ml), and synchronized these measurements with intrapharyngeal manometry. Comparisons were performed of bolus head and tail movement in relation to the timing of hyoid movement, contact between the arytenoid and epiglottic cartilages, and intrabolus pressures. Bolus head movement in the distal pharynx, as determined from flow plots, was relatively rapid. Initial bolus tail movement in the distal pharynx was delayed proportional to bolus volume, and once initiated, was slower than bolus head movement. Laryngeal exposure time, defined as the interval between bolus head arrival and tail departure at the hypopharyngeal recording sensor, increased as a function of bolus volume. The time interval between the initial anterior hyoid movement and bolus arrival at the larynx, determined by concurrent plotting of hyoid excursion and bolus head position, was constant despite increasing bolus volume. Similarly, the interval between epiglottic-arytenoid contact and bolus arrival was constant despite increased bolus volume. The early phase of intrabolus pressure was temporally associated with posterior movement of the tongue base and varied as a function of bolus volume, whereas late intrabolus pressure was temporally associated with initial pharyngeal wall movement and was not significantly volume dependent. These data indicate that the temporal relationship between laryngeal closure and bolus head flow remains constant despite changes of laryngeal exposure time to the bolus as a function of volume.

Adult↗

PubMed1992

Application of pyrolysis mass spectrometry to the investigation of outbreaks of food poisoning and non-gastrointestinal infection associated with Bacillus species and Clostridium perfringens.

Eighteen isolates of Bacillus species and 15 of Clostridium perfringens, all of which had been associated with outbreaks of either food poisoning or non-gastrointestinal infection (NGI), were examined for relatedness by pyrolysis mass spectrometry (PyMS). The PyMS-analysis correctly clustered all the groups of epidemiologically related isolates of both genera, and distinguished all the single, epidemiologically unrelated isolates of the same species. PyMS is a simple, rapid and inexpensive technique which can provide useful and accurate inter-strain comparisons within both the Bacillus and Clostridium genera in complete accord with conventional serological typing results.

Bacillaceae Infections↗

PubMed1992

Protein structure prediction from predicted residue properties utilizing a digital encoding algorithm.

Although many disparate methods have been applied to the problem, the accuracy of protein structural prediction still remains disappointingly low, averaging about 65% correct secondary structure assignment. A novel predictive method is presented here, which attempts to address some of the shortfalls inherent in representing a protein as a simple text-like sequence of amino acids, by deriving pattern-matching data from the predicted physical properties of a protein chain rather than from the sequence itself. A unique binary encoding algorithm is used to enable the property profiles to be correlated with known secondary structure, and hence to predict secondary structures for proteins with unknown structures. By treating the sequence in this manner, predictive accuracies averaging over 75% have been achieved.

Algorithms↗

PubMed1992

Two-dimensional coupling by gap junctions in cultured gastric smooth muscle monolayers.

We studied intercellular transfer in cultured rabbit gastric smooth muscle cell monolayers after microinjection of electrotonic current or the fluorescent probe Lucifer yellow CH. Because cultured gastric muscle cells proliferate in vitro and form regular arrays of parallel spindle-shaped cells, we sought to assess the role of cell shape and orientation in determining two-dimensional coupling properties. With the use of electron microscopy, gap junctions were identified between adjacent cells. Northern blot analyses using specific cDNA probes demonstrated expression of mRNA for the gap junction protein connexin43. Dye injection of Lucifer yellow resulted in 97% transfer to at least one adjacent cell, and 88% of adjacent cells received dye. Electrophysiological studies were performed using two intracellular microelectrodes to measure electrotonic current flow between cells at varying interelectrode distances. Current flow in the monolayers was modeled using a modified two-dimensional analysis. Initial assessment showed that the ratio of calculated space constants (longitudinal axis/perpendicular axis) was 4.4, indicating anisotropic conditions. However, when a geometric transform was used to normalize the spindle-shaped cells to regular hexagons, the space constants became statistically equivalent (200 microns longitudinal, 256 microns perpendicular). These results suggest that anisotropy of current flow in the monolayer of gastric smooth muscle cells was due primarily to the shape of the cells and not to intrinsic membrane properties or the distribution of gap junctions.

Animals↗

PubMed1992

The effect of study design on in situ treatment of carious enamel lesions.

The aim of this exploratory study was to investigate the influence of several factors on changes in the mineral content of carious enamel lesions treated in situ. The study involved 36 adult volunteers who used either a non-fluoride toothpaste or one of two fluoride toothpastes (1000 or 1500 ppm F). Human enamel specimens were prepared and attached to partial dentures as described previously (Schäfer, 1989) and treated in situ for between three and six weeks. The mineral content of lesions was determined by microradiography and computerized densitometry. The factors investigated in this study included study length, frequency of treatment, trial design, patient compliance, patient diet, and previous caries experience of the patient. The effects observed were small, relative to that of the treatment, and not statistically significant (p greater than 0.05). However, the trends in the data were all as would be intuitively predicted. Study duration correlated positively with observed lesion mineral content. Lesions worn by panelists using a fluoride toothpaste for six weeks contained greater levels of mineral with respect to placebo than did those in panelists on a three-week study. The residual variations in the three phases of the study were found to be similar, suggesting that there is no advantage in these studies having a cross-over design. Brushing frequency also correlated positively with observed lesion mineral content, with panelists brushing three times per day with a fluoridated dentifrice having lesions with greater levels of mineral, with respect to placebo, than those brushing twice per day. Overall, no clear relationship between reported diet and changes in lesion mineral levels was apparent.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Oral fluoride measurements for estimation of the anti-caries efficacy of fluoride treatments.

The aims of this work were (a) to assess the oral bioavailability of fluoride delivered from dentifrices and (b) to test for a possible link between the results and clinical data obtained with the same dentifrices. Oral fluoride concentrations were measured in samples of saliva and plaque taken from seven subjects, after use of dentifrices which contained 0, 1000, 1500, and 2500 micrograms F/g as sodium monofluorophosphate. Salivary fluoride in samples obtained within the first few hours after a single dentifrice application, or up to 20 h after four weeks' daily use, increased with increasing F content of the dentifrice. For example, the mean zero-time intercepts of the second phase of salivary fluoride clearance curves for the above dentifrices were 0.46, 1.48, 1.88, and 3.03 mumol F/L, respectively. Plaque fluoride measured after four weeks' daily use of the dentifrices exhibited similar dose-response behavior. Linear regression analysis showed these trends to be statistically significant for both saliva (p less than 0.001) and plaque (p less than 0.025). Mean saliva and plaque fluoride concentrations were inversely associated with mean three-year caries increments for the three fluoride-containing dentifrices obtained in a recent clinical trial: DMFS scores 6.80, 6.33, and 5.71, respectively (Stephen et al., 1988). This suggests that oral fluoride measurements are a valuable in vivo method for the evaluation of the potential anti-caries efficacy of fluoride-containing dental products.

Adult↗

PubMed1992

Intra-oral models to assess cariogenicity: evaluation of oral fluoride and pH.

The main purpose of this paper is to review the various methods used for evaluation of fluoride retention in saliva, plaque, and enamel following application of topical anti-caries treatments such as F dentifrices and F mouthwashes. Such methods monitor delivery of fluoride to the site of action, the mouth, and so can be regarded as assessing potential for treatment action. It is concluded that intra-oral fluoride measurements are appropriate to support bioequivalence claims for anti-caries treatments, provided that particular chosen methods have been calibrated against clinical data. Studies purporting to show superiority are of interest mechanistically, but links to caries are not sufficiently understood to define superiority claims. A wide variety of methods has been used for determination of the fluoride content of enamel. Of these, well-established methods such as the micro-drill and acid-etch procedures are appropriate for routine comparative testing, whereas sophisticated instrumental techniques such as SIMS are more appropriate for detailed mechanistic studies. Intra-oral pH measurements are also relevant to many topical treatments. Single-site determinations in plaque are preferred, but for comparative studies non-specific determinations may be adequate.

Dental Caries↗

PubMed1991

Human listeriosis and paté: a possible association.

OBJECTIVES: To study trends in human listeriosis and determine possible sources of infection. DESIGN: Descriptive analysis of laboratory reports of human listeriosis together with a survey of subtypes of Listeria monocytogenes isolated from patients and foodstuffs and an interview survey of patients to obtain food histories. SETTING: United Kingdom and Republic of Ireland 1985 to 1990. RESULTS: There was a near doubling in the incidence of human listeriosis in England, Wales, and Northern Ireland between 1985 and mid-1989 followed by a sharp decline. The upsurge in cases was caused largely by two strains of L monocytogenes, which accounted for 30-54% of the annual totals. These strains were less common before 1987 and after July 1989. A survey of paté in England and Wales in July 1989 showed that it frequently contained L monocytogenes. A similar survey in July 1990 showed a reduction in the proportions of samples contaminated. In 1989 patés from a single plant (manufacturer Y) were more likely to be contaminated by L monocytogenes and at higher levels than those from other producers. Most strains of L monocytogenes recovered from manufacturer Y's paté in 1989 were indistinguishable from those responsible for the 1987-9 upsurge in human listeriosis and were uncommon among isolates from patés from other manufacturers and from a wide range of other foodstuffs. Patients infected with the types of L monocytogenes found in paté were significantly more likely to have recently eaten paté than those affected by other strains. The start of the decline in numbers of cases of listeriosis coincided with government health warnings on paté consumption and the suspension of supplies from manufacturer Y. CONCLUSIONS: Contamination of paté was a likely contributory cause of the increase in the incidence of listeriosis between 1987 and 1989.

England↗

PubMed1991

Anticalculus effect of a dentifrice containing 0.5% zinc citrate trihydrate.

A doubleblind 3-month anticalculus clinical study was conducted to determine the magnitude of the antitartar effect to be derived from use of a 0.5% zinc citrate dentifrice. From a population of 1600 subjects exhibiting calculus, 1210 subjects (age 18 and over) were selected and received a dental prophylaxis. The subjects were initially stratified on the basis of calculus score, age, and sex, then allocated randomly to a 3-month usage period of one of two treatment groups. These were a dentifrice containing 0.5% zinc citrate or a control dentifrice without zinc citrate. Calculus was assessed using the Volpe-Manhold Index. Oral soft tissue status was assessed throughout the course of the study. At the conclusion of the study 964 subjects had completed the trial: 486 using the zinc citrate dentifrice and 478 using the control. The results showed that the mean calculus scores in the group using the dentifrice containing zinc citrate were 13.7% lower than those of the group using the control dentifrice. This finding was statistically significant (P less than 0.05). No adverse effects related to the use of either dentifrice were observed.

Adult↗

PubMed1991

ATP-dependent control of steady-state cytosolic calcium in cultured gastric smooth muscle.

The regulation of intracellular calcium uptake and release in cultured gastric smooth muscle cells was studied in saponin-permeabilized cells derived from the rabbit antrum. Cells were studied in an ATP-regenerating medium in which the value of the ATP-to-ADP ratio was fixed by variation of the relative concentrations of creatine and creatine phosphate in the presence of a constant concentration of adenine nucleotides and creatine kinase. Free calcium in the medium was measured through the use of the fluorescent probe fura-2. As the ratio of ATP/ADP was increased (8.5, 55.0, and 155.0), the rate of calcium sequestration was increased, resulting in a decrease of steady-state free calcium (275.2, 178.4, and 98.1 nM, respectively). The addition of glucose (5 mM) and hexokinase (15 U/ml), which results in an increase of ADP due to the phosphorylation of glucose in the medium, caused an increase of free calcium concentration to a new set point of approximately 400 nM. Mitochondrial blockade with antimycin A before permeabilization had no effect on calcium sequestration or the resultant free calcium concentration, indicating that under physiological conditions calcium is sequestered predominantly into nonmitochondrial storage sites. Specific variation of ATP/ADP had no effect on the concentration dependence of inositol trisphosphate-induced calcium efflux, suggesting the functional independence of intracellular calcium influx and efflux pathways. These results indicate a significant role for cytoplasmic ATP/ADP in the control of intracellular calcium sequestration and the regulation of steady-state calcium concentration in cultured gastrointestinal smooth muscle cells.

Adenosine Diphosphate↗