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Biomedical subjects

M Silverman

Publications and source records attributed to M Silverman.

At least 235 records · Page 13Linked to original sources
PubMed1989

Identification of a locus controlling expression of luminescence genes in Vibrio harveyi.

Mutagenesis with transposon mini-Mulac was used to identify loci containing genes for bioluminescence (lux) in the marine bacterium Vibrio harveyi. Transposon insertions which resulted in a Lux- phenotype were mapped to two unlinked regions of the genome. Region I contained the luxCDABE operon which was previously shown to encode the enzymes luciferase and fatty acid reductase, which are required for light production. The other locus, region II, which was identified for the first time in this study, appeared to have a regulatory function. In Northern blot analysis of mRNA from mutants with defects in this region, no transcription from the luxCDABE operon could be detected. Strains with transposon-generated lux::lacZ gene fusions were used to analyze control of the transcription of these regions. Expression of luminescence in the wild type was strongly influenced by the density of the culture, and in strains with the lacZ indicator gene coupled to the luxCDABE operon, beta-galactosidase synthesis was density dependent. So, transcription of this operon is responsive to a density-sensing mechanism. However, beta-galactosidase synthesis in strains with lacZ fused to the region II transcriptional unit did not respond to cell density. The organization and regulation of the lux genes of V. harveyi are discussed, particularly with regard to the contrasts observed with the lux system of the fish light-organ symbiont Vibrio fischeri.

Blotting, Southern↗
PubMed1989

Minitek urea disk test, a sensitive and cost-effective method to screen for Campylobacter pylori in gastric biopsies.

One hundred fifty-five biopsy specimens from the gastric mucosa of 81 patients undergoing routine endoscopy procedures were tested for the presence of Campylobacter pylori by three methods: Gram stain, culture, and modified Minitek, a rapid urea disk test (BBL Microbiology Systems, Cockeysville, Md.). Twenty-nine patients were infected with C. pylori. Sensitivities and specificities of detection were 100 and 94% with the Minitek test and 93 and 100% with Gram stain, respectively. Rapid testing by the urea disk is a simple, cost-effective, and accurate method for detecting the presence of C. pylori in gastric biopsy specimens.

Bacteriological Techniques↗
PubMed1989

Management of asthma: a consensus statement.

In developing these international guidelines there were several unifying themes in the diagnosis and simple management of childhood asthma. For the purposes of the meeting, asthma was operationally defined as 'episodic wheeze and/or cough in a clinical setting where asthma is likely and other rarer conditions have been excluded'. In making a diagnosis of asthma, a full history is a prerequisite. Additional tests are only used to support clinical impression and to provide objective evidence for therapeutic recommendations. General features of a multidisciplinary approach include an appreciation of the importance of psychosocial factors, counselling, and education. Drugs should be prescribed in a rational sequence: beta 2-stimulants for mild episodic wheeze; sodium cromoglycate for mild to moderate asthma; inhaled steroids for moderate to severe asthma; with xanthines, ipratropium bromide, and oral steroids having their place in more persistent and severe cases. Children and their parents should be reassured that if asthma is properly controlled there is no reason why the child should not lead a normal and physically active life. The management of asthma is rewarding and return to 'normal' lifestyle is nearly always possible with active participation in sporting activities.

Acute Disease↗
PubMed1989

Lung function in children of low birth weight.

Lung function was recorded in a cohort of 130 age specific children of low birth weight (under 2000 g) and a reference population of 120 unselected local schoolchildren at 7 years of age. Children of the cohort were similar in height and forced vital capacity to the reference group, but had significantly reduced forced expiratory volume in 0.75 second and expiratory flow indices. Although neonatal respiratory illness was associated with reduced airway function, we were unable to confirm that this was a consequence of oxygen treatment or mechanical ventilation. Low birth weight, however, was closely associated with poor airway function independent of neonatal respiratory illness. Other factors of importance included the male gender and maternal smoking. The reduction in airway function observed in the low birthweight children was associated with cough but not wheeze. The disparity between the relatively well preserved vital capacity and reduced airway function suggests that very low birth weight, and hence prematurity, has its greatest effect on the subsequent growth of airway function. The absence of an association between neonatal oxygen score or mechanical ventilation and childhood lung function suggests that the long term effect of neonatal respiratory treatment is small compared with that of birth weight, maternal smoking, and male sex.

Birth Weight↗
PubMed1989

Respiratory symptoms in children of low birth weight.

We recorded the respiratory history by questionnaire in a 7 year old cohort of children whose birth weight was under 2000 g and an unselected reference group of local schoolchildren of the same age. Complete data were obtained in 121 low birthweight children (90% of those studied): 62 who had no neonatal respiratory illness, 25 who had oxygen treatment only, and 34 who received mechanical ventilation (of whom 10 had bronchopulmonary dysplasia). The low birthweight children were no more likely to wheeze than the reference group, but frequent and troublesome cough was significantly more common, especially among children of very low birth weight (under 1500 g) who had received neonatal respiratory treatment. Neonatal mechanical ventilation was not associated with increased symptoms when compared with neonatal oxygen treatment alone. The prevalence of cough at the age of 7 was independently associated with the level of neonatal intensive care as defined by oxygen score. Although there was no excess of wheeze in the cohort compared with the reference group, there was a weak correlation between wheeze and the neonatal oxygen score as well as with maternal smoking. Loss of schooling due to respiratory symptoms in the nine months before this study was no greater in children of low birth weight than in the reference group.

Cohort Studies↗
PubMed1989

In vivo indicator dilution kinetics of PAH transport in dog kidney.

In vivo multiple indicator-dilution (MID) data were analyzed using a computer-assisted mathematical model of transepithelial cell transport to determine p-aminohippuric acid (PAH) transport kinetics across the proximal tubular antiluminal (ALM) and luminal (LM) membranes. A bolus of 125I-labeled albumin (plasma reference), [14C]creatinine (interstitial reference), and tracer [3H]PAH was injected into the left renal artery of anesthetized mongrel dogs (n = 21), and immediate serial sampling of the left renal venous and left and right urine outputs was performed (control). MID runs were then repeated in the same dog following intravenous infusion of unlabeled PAH. For all plasma PAH concentrations ([PAH]P), the steady-state unidirectional flux coefficients were calculated at the ALM and LM. The computer-derived unidirectional flux coefficients were in keeping with active ALM transport and passive, carrier-mediated LM transport. The Km calculated for ALM uptake (interstitium to cell) was 0.51 mM. PAH transport was completely inhibited by probenecid. As [PAH]P increased, the renal vein mean transit time ratio t[3H]PAH/t[14C]creatinine was greater than 1.0, indicating backflux from cells into the interstitium, then declined toward unity, as ALM and LM transport became saturated. This study, which used PAH as a model substrate demonstrated the feasibility of utilizing computer-assisted mathematical models to quantitate the kinetics of transepithelial transport from in vivo experimentation.

Animals↗
PubMed1989

A D-mannose transport system in renal brush-border membranes.

Dog renal brush-border membrane vesicles (BBMV) from whole kidney cortex contain both low-affinity, high-capacity and high-affinity, low-capacity Na-dependent D-glucose cotransporters. D-Mannose is an epimer of D-glucose, differing in structure only in the axial, rather than equatorial, orientation of the hydroxyl group at the C-2 position of the pyranose ring. Uptake experiments of radioactive sugars into BBMV by standard Millipore filtration were performed to determine whether D-mannose shares either, or both, of the D-glucose carriers or if it is transported by an independent system. Transport of D-mannose occurs into an osmotically active space and is saturable and sodium dependent with a 1:1 Na:D-mannose stoichiometry, Km of 0.063 mM, Vmax of 3.6 nmol.mg-1.min-1, 25 degrees C, and pH 7.4. When an NaSCN electrochemical gradient was present, an "overshoot" was present, indicating active cotransport. Up to 50 mM D-mannose did not inhibit sodium-dependent D-glucose or alpha-methylglucoside uptake (0.01-20 mM). Sodium-dependent D-mannose uptake was inhibited by the following compounds in order of decreasing effectiveness: fructose greater than mannoheptulose greater than 2-deoxy-D-glucose greater than 2-fluoro-2-deoxy-D-glucose much greater than phloretin, cytochalasin B, galactose, 3-O-methyl-D-glucose, and L-mannose. Phlorizin also inhibited D-mannose uptake, but the high concentration required and the fact that a competitive pattern of inhibition could not be demonstrated contrasted with its effect on D-glucose transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Immunocytochemical characterization of cells in rat glomerular culture.

Identification and characterization of cells in glomerular tissue culture has been an ongoing concern of experimental renal biologists. We examined the immunocytochemical staining profiles of primary and passaged rat glomerular cultures using a battery of commercially available antisera. In all culture systems examined, two distinct cell populations could be distinguished. One cell type stained positively for desmin and had ultrastructurally smooth muscle features typical of contractile mesangial cells. The second cell type proliferated in a manner classically described for "epithelial" cells but, intriguingly, did not express any of the numerous epithelial markers tested. The second cell population may represent an undifferentiated reserve cell type. Immunocytochemical methods offer an independent modality to the evaluation of cells which proliferate in glomerular cell culture.

Animals↗
PubMed1988

Flagellar dynamometer controls swarmer cell differentiation of V. parahaemolyticus.

Swarmer cell genes, laf, are induced when V. parahaemolyticus is grown on the surface of solidified media, embedded in solidified media, suspended in viscous media, or agglutinated with antibody in liquid media. These conditions have in common the constraint of the movement of the polar flagellum. To test the hypothesis that the polar flagellum functions as a sensor necessary for control of swarmer cell formation, we have constructed a variety of mutations in genes encoding components of the polar flagellum, fla. The consequence of such mutations is the constitutive expression of laf genes. So, the performance of the polar flagellum is coupled to the transcription of laf genes such that when function is perturbed, either physically or genetically, swarmer cell genes are induced. Because the polar flagellum appears to be capable of sensing external forces influencing its motion, we suggest it is acting as a dynamometer.

Culture Media↗