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Biomedical subjects

C Fritz

Publications and source records attributed to C Fritz.

At least 19 recordsLinked to original sources
PubMed2005

Liquid drainage through aqueous foam: study of the flow on the bubble scale.

Macroscopic properties of foams are highly dependent on the liquid volume fraction, which has motivated many studies on foam drainage in the last decade. Theoretical developments and recent experimental results have suggested that two macroscopic drainage regimes could be expected, in relation with flow transitions occurring at the microscopic level, essentially in the Plateau border channels. We have constructed a setup, the Plateau border apparatus, to study the hydrodynamics of a single Plateau border channel, focusing on the surface properties of the foaming solution. Experimental results have shown that the actual theoretical models only partially predict the dissipation of liquid flow through a Plateau border channel. The major discrepancies can be explained considering additional dissipation processes related to the properties of the interface, and to the liquid flows induced in adjoining films as the liquid flows in the channel. Evidence of the hydrodynamic coupling between the channel and the adjoining films is given in the paper.

Journal Article↗
PubMed2000

Anaerobic nitrate reductase (narGHJI) activity of Mycobacterium bovis BCG in vitro and its contribution to virulence in immunodeficient mice.

Mycobacterium tuberculosis and Mycobacterium bovis cause tuberculosis, which is responsible for the deaths of more people each year than any other bacterial infectious disease. Disseminated disease with Mycobacterium bovis BCG, the only currently available vaccine against tuberculosis, occurs in immunocompetent and immunodeficient individuals. Although mycobacteria are obligate aerobes, they are thought to face an anaerobic environment during infection, notably inside abscesses and granulomas. The purpose of this study was to define a metabolic pathway that could allow mycobacteria to exist under these conditions. Recently, the complete genome of M. tuberculosis has been sequenced, and genes homologous to an anaerobic nitrate reductase (narGHJI), an enzyme allowing nitrate respiration when oxygen is absent, were found. Here, we show that the narGHJI cluster of M. tuberculosis is functional as it conferred anaerobic nitrate reductase activity to Mycobacterium smegmatis. A narG mutant of M. bovis BCG was generated by targeted gene deletion. The mutant lacked the ability to reduce nitrate under anaerobic conditions. Both mutant and M. bovis BCG wild type grew equally well under aerobic conditions in vitro. Histology of immunodeficient mice (SCID) infected with M. bovis BCG wild type revealed large granulomas teeming with acid-fast bacilli; all mice showed signs of clinical disease after 50 days and succumbed after 80 days. In contrast, mice infected with the mutant had smaller granulomas containing fewer bacteria; these mice showed no signs of clinical disease after more than 200 days. Thus, it seems that nitrate respiration contributes significantly to virulence of M. bovis BCG in immunodeficient SCID mice.

Animals↗
PubMed1997

The complete genome sequence of the gram-positive bacterium Bacillus subtilis.

Bacillus subtilis is the best-characterized member of the Gram-positive bacteria. Its genome of 4,214,810 base pairs comprises 4,100 protein-coding genes. Of these protein-coding genes, 53% are represented once, while a quarter of the genome corresponds to several gene families that have been greatly expanded by gene duplication, the largest family containing 77 putative ATP-binding transport proteins. In addition, a large proportion of the genetic capacity is devoted to the utilization of a variety of carbon sources, including many plant-derived molecules. The identification of five signal peptidase genes, as well as several genes for components of the secretion apparatus, is important given the capacity of Bacillus strains to secrete large amounts of industrially important enzymes. Many of the genes are involved in the synthesis of secondary metabolites, including antibiotics, that are more typically associated with Streptomyces species. The genome contains at least ten prophages or remnants of prophages, indicating that bacteriophage infection has played an important evolutionary role in horizontal gene transfer, in particular in the propagation of bacterial pathogenesis.

Bacillus subtilis↗
PubMed1997

The nucleotide sequence of Saccharomyces cerevisiae chromosome XIV and its evolutionary implications.

In 1992 we started assembling an ordered library of cosmid clones from chromosome XIV of the yeast Saccharomyces cerevisiae. At that time, only 49 genes were known to be located on this chromosome and we estimated that 80% to 90% of its genes were yet to be discovered. In 1993, a team of 20 European laboratories began the systematic sequence analysis of chromosome XIV. The completed and intensively checked final sequence of 784,328 base pairs was released in April, 1996. Substantial parts had been published before or had previously been made available on request. The sequence contained 419 known or presumptive protein-coding genes, including two pseudogenes and three retrotransposons, 14 tRNA genes, and three small nuclear RNA genes. For 116 (30%) protein-coding sequences, one or more structural homologues were identified elsewhere in the yeast genome. Half of them belong to duplicated groups of 6-14 loosely linked genes, in most cases with conserved gene order and orientation (relaxed interchromosomal synteny). We have considered the possible evolutionary origins of this unexpected feature of yeast genome organization.

Base Sequence↗
PubMed1997

Silent period following transcranial magnetic stimulation: a study of intra- and inter-examiner reliability.

Transcranial magnetic stimulation-evoked silent period (SP) has been attributed largely to the activity of intracortical inhibitory systems and recent reports provided evidence that it is a useful indicator of central motor disturbances. We studied the intra- and inter-examiner reliability of SP measurements in 28 healthy subjects. In 15 subjects SP measurements were performed by one single examiner and repeated by the same examiner 3 days and 7 days later, showing a high degree of intra-examiner reliability over time. In another subgroup consisting of 13 volunteers SP measurements were performed on the same subject by three different examiners, demonstrating a higher level of variability. In both subgroups we found a high interindividual variability ranging from 44-258 ms and a considerably lower side-to-side difference within subjects. Our results suggest that longitudinal assessments of the SP in patients with central motor involvement should optimally be performed by a single examiner. Regarding the wide range of possible SP durations in healthy subjects the intraindividual side-to-side symmetry seems to be the most valuable parameter.

Adult↗
PubMed1996

The role of prostaglandins E2 and F2 alpha in ultraviolet radiation-induced cortical cataracts in vivo.

PURPOSE: Previous work has shown that exposure of lens epithelial cells or rabbit eyes in vivo to ultraviolet B (UVB) radiation enhanced prostaglandin (PG)E2 synthesis. Such enhanced PGE2 synthesis was related to the increased DNA synthesis that followed UVB exposure. The current study examined the relationship between enhanced prostaglandin synthesis and UVB-induced cataract formation. METHODS: Seventy albino (New Zealand white) rabbit eyes were exposed to UVB radiation in vivo. Fluence of radiation at the cornea was 2.8 J/cm2, 5.6 J/cm2, or 11.2 J/cm2. Eyes were examined 24 hours after UVB exposure and for as long as 10 days by slit lamp biomicroscopy. Mass spectrometry was used to measure PGE2, PGF2 alpha, and 6-keto-PGF1 alpha content of the lens and iris-ciliary body using authentic standards. To determine the effect of inhibition of prostaglandin synthesis on UVB-induced cataract formation, animals were given indomethacin intraperitoneally. Other pharmacologic agents, such as PGE2, PGF2 alpha, and misoprostol, were applied topically to the eye. The effect of UVB on K+ pump was determined by incubating isolated lenses with [86Rb+]. RESULTS: Twenty-four hours after UVB exposure, PGE2 and PGF2 alpha concentrations in aqueous humor were increased by 100- and 30-fold, respectively. Lens PGE2 and PGF2 alpha increased by 6- and 4-fold, respectively, after UVB radiation exposure. Pretreatment of animals with indomethacin prevented the rise in lens and aqueous humor PGE2 and PGF2 alpha levels. Furthermore, indomethacin was partially protective against UVB cataract formation and lowered cataract severity from stage 3 to stage 1, but it did not prevent UVB-induced lens changes completely. Topical application of PGE2 before UVB exposure completely prevented cataract formation in the UVB-exposed eye. In contrast, topical administration of PGF2 alpha increased cataract severity. UVB-induced cataract formation preceded changes in [86Rb]+ uptake in lenses subsequently incubated in K(+)-free Tyrode's. CONCLUSIONS: Enhanced synthesis of cyclooxygenase products of arachidonic acid metabolism in the lens is associated with UVB-induced cataract formation in albino rabbit eyes, and inhibition of cyclooxygenase by indomethacin decreased the severity of cataracts. PGE2, the principal arachidonic acid metabolite, appears to have a protective role because pretreatment of the eye with topical PGE2 completely prevented UVB-induced cataract formation, whereas PGF2 alpha increased the severity of the cataract. The evidence presented for a role of PGF2 alpha in the development of cataract suggests that caution be exercised in the use of PGF2 alpha derivatives in the therapy of glaucoma.

6-Ketoprostaglandin F1 alpha↗
PubMed1995

Transcranial magnetic stimulation-evoked inhibition of voluntary muscle activity (silent period) is impaired in patients with ischemic hemispheric lesion.

BACKGROUND AND PURPOSE: Transcranial magnetic stimulation of the motor cortex is well established as a valuable method for noninvasive examination of the central motor system. In addition to exciting corticospinal cells and evoking a direct motor response, the magnetic stimulus delivered during voluntary activity produces a prolonged postexcitatory inhibition (silent period) of activity. We investigated silent period changes in patients with ischemic stroke of different clinical degrees. METHODS: Standardized transcranial magnetic stimulation during sustained muscle contraction was performed at the vertex. Electromyographic activity was recorded via surface electrodes placed over the abductor digiti minimi muscle on both sides. We examined 50 patients with stroke (divided into three subgroups according to the degree of impairment) and 50 healthy control subjects. RESULTS: In the control group we found no statistically significant interside difference in the duration of the silent period, whereas a marked interindividual variation was found. In patients with prior minor stroke who showed no residual motor disturbance, we found a significant prolongation of the postexcitatory inhibition recorded from the affected side compared with the healthy side. This interside discrepancy was even more pronounced in patients with minor hemiparesis and patients with moderate hemiparesis. CONCLUSIONS: Our findings suggest that the measurement of the silent period elicited by transcranial magnetic stimulation is a useful and sensitive neurophysiological parameter in the management of stroke. Particularly in the subgroup of patients with no residual clinical signs of central motor impairment, it is capable of detecting subclinical motor function disturbances.

Adult↗
PubMed1994

Complete DNA sequence of yeast chromosome II.

In the framework of the EU genome-sequencing programmes, the complete DNA sequence of the yeast Saccharomyces cerevisiae chromosome II (807 188 bp) has been determined. At present, this is the largest eukaryotic chromosome entirely sequenced. A total of 410 open reading frames (ORFs) were identified, covering 72% of the sequence. Similarity searches revealed that 124 ORFs (30%) correspond to genes of known function, 51 ORFs (12.5%) appear to be homologues of genes whose functions are known, 52 others (12.5%) have homologues the functions of which are not well defined and another 33 of the novel putative genes (8%) exhibit a degree of similarity which is insufficient to confidently assign function. Of the genes on chromosome II, 37-45% are thus of unpredicted function. Among the novel putative genes, we found several that are related to genes that perform differentiated functions in multicellular organisms of are involved in malignancy. In addition to a compact arrangement of potential protein coding sequences, the analysis of this chromosome confirmed general chromosome patterns but also revealed particular novel features of chromosomal organization. Alternating regional variations in average base composition correlate with variations in local gene density along chromosome II, as observed in chromosomes XI and III. We propose that functional ARS elements are preferably located in the AT-rich regions that have a spacing of approximately 110 kb. Similarly, the 13 tRNA genes and the three Ty elements of chromosome II are found in AT-rich regions. In chromosome II, the distribution of coding sequences between the two strands is biased, with a ratio of 1.3:1. An interesting aspect regarding the evolution of the eukaryotic genome is the finding that chromosome II has a high degree of internal genetic redundancy, amounting to 16% of the coding capacity.

Base Composition↗
PubMed1994

Complete DNA sequence of yeast chromosome XI.

The complete DNA sequence of the yeast Saccharomyces cerevisiae chromosome XI has been determined. In addition to a compact arrangement of potential protein coding sequences, the 666,448-base-pair sequence has revealed general chromosome patterns; in particular, alternating regional variations in average base composition correlate with variations in local gene density along the chromosome. Significant discrepancies with the previously published genetic map demonstrate the need for using independent physical mapping criteria.

Base Sequence↗
PubMed1992

[Spontaneous dissection of the internal carotid artery].

A typical case history of spontaneous dissection of the internal carotid artery is presented. In young patients with cerebral ischemia, initial pain in the affected side of the head and neck, a possible provocative mechanism and a transient or even persistent Horner's syndrome are highly suggestive. The angiographic picture of carotid artery dissection is characteristic. Spontaneous resolution is common, and recurrence rare. Surgical treatment can therefore be reserved for individual cases with recurrent ischemia and caused by emboli originating in the dissected segment of the artery.

Aortic Dissection↗
PubMed1985

Maturation of Rb+ and PAH accumulation by rabbit anterior uvea and choroid plexus.

In vitro accumulation of radioactive para-aminohippuric acid (3H-PAH) and rubidium (86Rb+) by the anterior uvea, ciliary processes, and the choroid plexus was evaluated in tissues from newborn and various aged rabbits. Accumulation of PAH was present in the anterior uvea at 1 day of age (tissue to media ratio, T/M, of 2.1 +/- 0.2) and remained at this level for the first 14 days of life. Accumulation did not rise to adult levels until 21 days of age (T/M 5.5 +/- 0.6). Rubidium accumulation in the anterior uvea, a measure of Na+, K+-pump activity, was higher than adult values 6 hr after birth (T/M25.2 +/- 0.9). Activity remained elevated through day 28 and did not fall to adult levels until day 60 (T/M 13.4 +/- 0.6). Accumulation studies on isolated ciliary processes were similar to those obtained from anterior uveal tissue. Daily subcutaneous injections of penicillin (300,000 units/kg/day) for 1 week had no effect on anterior uvea PAH accumulation (penicillin T/M was 1.7 +/- 0.1 and saline control T/M was 2.0 +/- 0.2). Accumulation of either 3H-PAH or 86Rb+ by the choroid plexus was present 1 day after birth in amounts that were similar to adult values and did not change during the 90 days of testing.

Aminohippuric Acids↗
PubMed1981

Transport and metabolism of pyridoxine in rabbit iris--ciliary body.

Isolated rabbit iris--ciliary body preparations were found to accumulate 3H-pyridoxine by a mechanism that was time- and temperature-dependent, saturable in part, but not altered by omission of oxygen or specific ions. Tissue accumulation was only partially energy-dependent, and metabolic inhibitors had only small effects. Other B6 vitamers markedly blocked accumulation. Metabolism of 3H-pyridoxine within the tissue was extensive. After 60 min incubation with 3H-pyridoxine, about 65% of the radioactivity in the iris--ciliary body was associated with phosphorylated vitamers which did not efflux from the tissue as readily as did the nonphosphorylated forms. Unaltered pyridoxine accounted for only 16% of intracellular 3H-B6, and this did not represent accumulation against a concentration gradient. A similar saturable uptake process occurred in vivo. These data were consistent with the hypothesis that pyridoxine was accumulated by facilitated diffusion with intracellular trapping of phosphorylated metabolites.

Animals↗