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Biomedical subjects

S C Brown

Publications and source records attributed to S C Brown.

At least 73 records · Page 4Linked to original sources
PubMed1993

Dystrophin as a mechanochemical transducer in skeletal muscle.

This review is primarily concerned with two key issues in research on dystrophin: (1) how the protein interacts with the plasma membrane of skeletal muscle fibres and (2) how an absence of dystrophin gives rise to Duchenne muscular dystrophy. In relation to the first point, we suggest that the post-translational acylation of dystrophin may contribute to its interaction with the plasma membrane. Regarding the second point, it is generally considered that an absence of dystrophin makes the plasma membrane susceptible to damage by contraction/relaxation cycles. In this connection, we propose that the progressive nature of Duchenne dystrophy, and the phenotypic characteristics of mdx mice, are more consistent with dystrophin functioning as a mechanical transducer that transmits growth stimuli from the enlarging skeleton to the muscle. On the basis of this hypothesis, dystrophin-deficient muscles would be unable to grow at the same rate as the skeleton.

Amino Acid Sequence↗
PubMed1993

Heterochromatin study demonstrating the non-linearity of fluorometry useful for calculating genomic base composition.

A novel procedure for calculating base-pair frequencies in whole genomes is reported. This has been developed during a study of the role of heterochromatin in microevolution. Closely related species of the Crepis praemorsa complex have similar karyotypes but for their heterochromatin. The changes in relative AT frequency between species have been attributed to heterochromatin sequences by in situ banding of chromosomes with two base-specific fluorochromes. The absolute genome size of species, measured by cytofluorometry, correlated positively with increased karyotypic heterochromatin, as did the proportion of AT bases in the DNA. However, the determination of base content has called for a curvilinear interpretation of data obtained with two base-specific fluorochromes (bisbenzimide Hoechst 33342 and mithramycin), in contrast to the commonly assumed but erroneous direct relationship between fluorescence intensity and base content. Essentially, the fluorochromes' requirements for a sequence of certain base-pairs lead to the notion of Coefficients of Overspecificity: the result is a simple formula for calculating the AT proportion in a genome relative to a reference species from cytometric data, taking account of ligand binding statistics. These statistics and probabilities of oligonucleotide binding are essentially the same.

Adenine↗
PubMed1993

Silica induces apoptosis in macrophages and the release of interleukin-1 alpha and interleukin-1 beta.

Resident adherent peritoneal cells selectively released high amounts of interleukin-1 (IL-1) activity when treated with silica. The use of anti-IL-1 antisera showed that both IL-1 alpha and IL-1 beta were present in supernatants of silica-treated macrophages. In contrast, intracellular IL-1 activity was totally neutralized by anti-IL-1 alpha antibodies and was easily converted into the mature IL-1 alpha form by autolysis in cytoplasmic extracts. Anion exchange chromatography clearly separated the two IL-1 species present in supernatants of silica-stimulated macrophages. Natural IL-1 beta was further characterized by chromatofocalization; it had an apparent isoelectric point, pI, in the range 8.3-8.6. In agreement with previous findings showing that IL-1 beta was released only by apoptotic cells, we have found that silica-treated macrophages underwent apoptosis. This was demonstrated by the characteristic laddering electrophoretic pattern of DNA extracted from silica-treated cells and by the morphology of macrophage nuclei stained with the DNA-specific dye DAPI. In addition, quantification of apoptotic cells was performed by a flow cytometric analysis based on the reduction of cellular DNA content exhibited by apoptotic cells. Treatment of macrophages with silica, therefore, results in an active process that promotes the processing and liberation of IL-1 beta.

Animals↗
PubMed1993

Digitaria streak geminivirus replicative forms are abundant in S-phase nuclei of infected cells.

We have analyzed the replication of Digitaria streak geminivirus (DSV) using flow cytometry. Nuclei from infected plants were sorted on the basis of their DNA content in the different phases of the cell cycle and viral DNA forms in them were analyzed. DSV replicative forms were much more abundant (up to 20 times in one experiment) in S-phase nuclei than in G0-G1 and G2 nuclei, while single-stranded viral DNA did not show such dramatic increase during any phase. DSV replicative forms constitute almost 90% of total viral DNA forms in S-phase nuclei. DSV replication seems to be synchronized with host DNA replication and might be primarily under control of host factors becoming available only at the G1/S boundary.

Blotting, Southern↗
PubMed1993

Recombinant human IL-6 expressed in E. coli undergoes selective N-terminal degradation: evidence that the protein consists of a stable core and a nonessential flexible N-terminal.

A synthetic gene for human interleukin-6 has been expressed in E. coli. The protein has been purified and renatured and has the same activity as natural human IL-6 using the 7TD1 cell proliferation assay. The protein undergoes specific cleavage by a thiol protease, yielding two new N-termini at Arg-9 and His-15. The truncated proteins retain full biological activity. The degradation results in the loss of sharp amide resonances in the 1H-NMR spectrum, and little change to the ultraviolet CD spectrum. Several amino acid type assignments could be made for these sharp amides using a DQF-COSY 2D-NMR experiment. The N-terminal 15 amino acids exist as a flexible, random coil, attached to a central structure.

Amino Acid Sequence↗
PubMed1993

A cytometric exercise in plant DNA histograms, with 2C values for 70 species.

An introduction is given to the literature concerning methods and objectives for cytometric DNA analysis of plant nuclei. This area has gained relevance with applications in plant breeding and seed production industries, where laboratories unfamiliar with cytometry are adopting the method. An extensive graphical guide to interpreting DNA histograms and their problems is given. Conversely, cytometry laboratories unfamiliar with plant sciences will find herein a guide, and references, to adapt their methods to plant material. A table of 2C values reassessed by flow cytometry for 70 plant species, plus the genome composition (GC%) in many instances, is also included.

Cell Cycle↗
PubMed1993

Satellite cell content in muscles of large and small mice.

Quantitative analyses of the satellite cell content in the biceps brachii muscle of mice genetically selected for high (QL) and low (QS) bodyweight showed that selection alters the total number of satellite cell nuclei rather than the relative proportions of nuclei in the myofibre and satellite cell populations. These findings are in accordance with those previously published for other tissues of these mice and support the hypothesis that regulatory mechanisms remain unaltered by selection pressure. Size at birth, however, is a reflection of nutritional status as well as genetic background, and comparisons between differently sized littermates within each of the lines showed a significant increase in satellite cell density in larger compared with smaller individuals. These differences between littermates were not accompanied by any alteration in myofibre nuclear density. It is therefore suggested that whilst both genetic and nutritional factors exert their effects on muscle growth through an influence on satellite cell division, both do so at different stages during the programme of satellite cell differentiation.

Animals↗
PubMed1992

Flow cytometric analysis of opposite effects of a monokine on proliferation and differentiation of murine B lymphocytes.

A 35,000 mw factor able to replace macrophages (FRM) in the induction of the in vitro antibody response to sheep erythrocytes has been isolated from the supernatant of murine resident peritoneal macrophage cultures. Purified FRM, when added at the outset of cultures, induced B cells to generate an antigen-specific antibody response. The signals provided by FRM in the process of B cell activation were analyzed using a polyclonal model. Cell cycle analysis by multiparameter flow cytometry after acridine orange staining showed that FRM, on its own, did not trigger the transition of B cells from the G0 to the G1 stage of the cell cycle. In addition, FRM affected neither the basal intracellular free calcium level ([Ca2+]i) nor the rapid increase in [Ca2+]i induced by crosslinking of membrane immunoglobulin (mIgM) with anti-mu antibodies. In parallel with its positive effect on B cell differentiation, FRM markedly reduced both proliferation and cell cycle progression of B cells stimulated with anti-mu plus interleukin 4 (IL-4). Indeed, the addition of FRM to such cultures led to a preferential accumulation of cells in the early G1 compartment of the cell cycle and to a decreased frequency of cells in all other phases including G1B, S and G2/M.

Animals↗
PubMed1992

The estimate of glomerular filtration rate during urography. Acceptability of a nonionic contrast medium as a marker of renal function.

RATIONALE AND OBJECTIVES: An estimate of glomerular filtration rate (GFR) may be obtained at the same time as urography by measuring the plasma clearance of the radiographic contrast medium using an x-ray fluorescence technique. It must be established whether the function measured or one modified by an effect of the contrast medium itself represents a true value. METHODS: Technetium 99m-DTPA (99mTc-DTPA) plasma clearance was measured in 21 patients using a single-injection technique, before, during, and after an intravenous injection of 50 mL of 350 mg I/mL iohexol. Iohexol clearance also was determined using an alternative single-injection, two-sample technique. RESULTS: The mean 99mTc-DTPA clearances before, during, and after contrast were 71.2, 71.5, and 70.7 mL/minute, respectively. The within-patient standard deviation in clearance values was 3.84 mL/minute. One factor repeat measures analysis of variance indicated no significant difference between the three measurements (F ratio = 0.24). Contrast and 99mTc-DTPA clearances performed simultaneously agreed closely (r = .976; ClDTPA = 1.02ClCon - 1.35). CONCLUSION: The authors conclude that no change in function is observed during or 48 hours after contrast injection. Imaging doses of iohexol can be used for GFR measurement during urography.

Aged↗
PubMed1992

The importance of renal function in the interpretation of diuresis renography.

Interpretation of the diuresis renogram is dependent on a full understanding of the factors that contribute to the washout curve, a major determinant being the urinary flow rate induced by the diuretic. Frusemide-induced flow rates were measured in 86 patients over a 30-min period and related to creatinine clearance in 39, 99mTc-DTPA clearance (glomerular filtration rate (GFR)) in 27, and 123I-Hippuran clearance (effective renal plasma flow) in 20. The flow rates 3 to 6 min and 15 to 18 min after administration of the diuretic received specific attention because of their importance to F + 20 and F - 15 diuresis renography respectively. The mean urinary flow rate 15 to 18 min after frusemide was 3.5 ml/min greater than at 3 to 6 min (P less than 0.001), explaining the value of the F - 15 renogram in further evaluating equivocal F + 20 curves. Linear relationships were observed between each parameter of function and the 3 to 6 min and 15 to 18 min periods as follows: creatinine clearance r = 0.66, r = 0.77; 99mTc-DTPA clearance r = 0.66, r = 0.77; 123I-Hippuran clearance r = 0.59, r = 0.71. From regression analysis of the data presented it is possible, with knowledge of total and split function, to predict single-kidney flow rates. It is demonstrated that these may commonly exceed flow rates used for perfusion studies if function is normal, but a single-kidney flow rate of 10 ml/min is unlikely to be attained if the single-kidney GFR is less than 15 ml/min.

Adult↗
PubMed1992

Delay in presentation and misdiagnosis of strangulated hernia: prospective study.

The purpose of this study was to examine the presentation and management of strangulated hernia. The clinical course of 54 patients was recorded. Twenty-one patients (39%) presented after 48 h from the onset of symptoms. Fifteen (28%) had a bowel resection and two (4%) died. Twenty (37%) patients had previously consulted their general practitioner about the hernia, but only seven had been referred for surgery. Five (25%) had been warned of the risk of strangulation. In the 32 (59%) patients previously aware of a hernia, delayed presentation was related to ignorance of the risk of strangulation (P less than 0.01). The strangulated hernia was misdiagnosed by the general practitioner in 17 (33%) patients (necessitating a second visit) and by the hospital registrar in eight (15%). We conclude that strangulated hernia is too often misdiagnosed and all patients who present with a hernia must be referred to a surgeon and warned about strangulation.

Adult↗
PubMed1991

Amphibian prolactins: activity in the eft skin transepithelial potential bioassay.

The effects of purified prolactins isolated from frogs (fPRL; Rana catesbeiana) and newts (nPRL; Cynops pyrrhogaster) were compared with those of ovine prolactin (oPRL) and thyrotropin releasing hormone (TRH) in the eft (Notophthalmus viridescens) skin transepithelial potential (TEP) bioassay. At total doses as low as 0.4 micrograms/animal, both fPRL and nPRL were as effective as oPRL in reducing eft skin TEP. By contrast, TRH at total doses as high as 400 micrograms/animal was ineffective in altering eft skin TEP. These data provide the first direct evidence that amphibian PRLs can exert significant physiological control over salamandrid integumental sodium transport.

Animals↗
PubMed1991

Iohexol clearance for the determination of glomerular filtration rate in clinical practice: evidence for a new gold standard.

X-ray fluorescence analysis provides a simple method of measuring glomerular filtration rate from the clearance of ordinary unlabeled radiographic contrast media. To measure the accuracy of iohexol clearance using a clinically simple 2-sample single injection technique, a comparison was made in 30 patients with classical continuous infusion techniques for plasma (y = 1.03x - 0.015, r = 0.981) and renal (y = 0.950x + 7.26, r = 0.964) iohexol clearance. A comparison was made with classical inulin clearance. The renal clearance of iohexol and inulin was virtually identical (y = 0.998x + 2.31, r = 0.986). Single injection iohexol clearance agreed closely with the renal inulin clearance (y = 0.947x + 4.92, r = 0.983) as did clearance based on a single 3-hour sample (y = 0.875x + 12.63, r = 0.962). Iohexol clearance using x-ray fluorescence is a simple, rapid and accurate alternative to inulin clearance for clinical and research purposes.

Adult↗
PubMed1991

Compartmental analysis and glomerular filtration in chick embryos.

We have developed microtechniques that allow the determination of compartmental fluid distribution and glomerular filtration rate in chick embryos during three significant developmental periods: phase 1, the developmental period when the mesonephros alone is functioning; phase 2, periods of simultaneous meso/metanephric kidney function; and phase 3, the period during late development when the metanephros completely replaces the degenerated mesonephros. Water content of tissues is greater in younger embryos (89.4 +/- 0.2%, day 10) compared with older animals (78.3 +/- 0.5%, day 18). Although all major tissue components show an absolute increase in mass during this period, the embryo proper increases at five times the rate of the extraembryonic tissues. Glomerular filtration rate increases during development from 0.61 +/- 0.08 ml/h at day 10 to 2.31 +/- 0.11 ml/h at day 18. Glomerular filtration rate scales to body mass with an allometric exponent identical to adult birds only if total tissue mass (embryo + membranes) is considered. Our data suggest that significant errors in allometry will be encountered when scaling measurements are made on embryonic or fetal amniotes without taking into consideration the extraembryonic tissues.

Animals↗
PubMed1991

Risk factors and operative mortality in surgery for colorectal cancer.

The operative mortality rate after surgery for colorectal carcinoma remains significant. A series of 578 patients has been studied prospectively. The features which most significantly affect operative mortality are the age of the patient, a history of loss of weight, limited preoperative patient mobility and the presence of intestinal obstruction with perforation of the bowel. By identifying high-risk groups of patients, attention may be focused on particular patients at risk, in order to reduce operative mortality.

Activities of Daily Living↗
PubMed1990

Analysis of the membrane potential of rat- and mouse-liver mitochondria by flow cytometry and possible applications.

Washed and purified rat- or mouse-liver mitochondria exhibiting high membrane integrity and metabolic activity were studied by flow cytometry. The electrophoretic accumulation/redistribution of cationic lipophilic probes, rhodamine 123, safranine O and a cyanine derivative, 3,3'-dihexyloxadicarbocyanine iodide, during the energization process was studied and was consistent with the generation of a negative internal membrane potential. An exception to this was nonylacridine orange which spontaneously bound to the mitochondrial membrane by hydrophobic interactions via its hydrocarbon chain. Energized purified mitochondria stained with potentiometric dyes exhibited both higher fluorescence and population homogeneity than the non-energized or deenergized (nigericin plus valinomycin) mitochondria. By contrast, under non-energized or deenergized conditions, the mitochondrial population exhibited fluorescence intensity heterogeneity related to the residual membrane potential; two subpopulations were evident, one of low fluorescence which may be related to the autofluorescence of the mitochondria (plus non-specific dye binding) and a second population which exhibited high fluorescence. Flow cytometry of the unpurified, simply washed, rat-liver mitochondria stained with rhodamine 123, a classically used dye, provided evidence of their heterogeneity in terms of light-scattering properties and membrane-potential-related fluorescence. One third of the washed mitochondria were found to be non-functional by such assays. The fluorescence of purified rat-liver mitochondria due to the membrane potential built up by endogenous substrates indicates heterogeneity of the mitochondrial population with respect to levels of endogenous substrates. The low-angle light scattering increases upon energization and provides some original information about the shape and modification of the inner mitochondrial conformation accompanying the energization. The heterogeneity of the rat liver mitochondrial population, from a structural, metabolic (existence of endogenous substrates) and functional (active and non-active mitochondrial population dispersion) point of view could thus be demonstrated by flow-cytometry analysis. Two animal models were examined with regard to the alteration of the mitochondrial membrane potential under the effects of drugs (rat-liver mitochondria), and the effects of ammonium toxicity (mouse-liver mitochondria). These results are promising and open new perspectives in the study of mitochondriopathies.

Ammonia↗
PubMed1990

Solution structures of human transforming growth factor alpha derived from 1H NMR data.

The 600-MHz 1H NMR spectrum of the des-Val-Val mutant of human transforming growth factor alpha (TGF-alpha) was reassigned at pH = 6.3. The conformation space of des-Val-Val TGF-alpha was explored by distance geometry embedding followed by restrained molecular dynamics refinement using NOE distance constraints and some torsion angle constraints derived from J-couplings. Over 80 long-range NOE constraints were found by completely assigning all resolved cross-peaks in the NOESY spectra. Low NOE constraint violations were observed in structures obtained with the following three different refinement procedures: interactive annealing in DSPACE, AMBER 3.0 restrained molecular dynamics, and dynamic simulated annealing in XPLOR. The segment from Phe15 to Asp47 was found to be conformationally well-defined. Back-calculations of NOESY spectra were used to evaluate the quality of the structures. Our calculated structures resemble the ribbon diagram presentations that were recently reported by other groups. Several side-chain conformations appear to be well-defined as does the relative orientation of the C loop to the N-terminal half of the protein.

Computer Simulation↗