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D Brown

Publications and source records attributed to D Brown.

At least 199 records · Page 11Linked to original sources
PubMed2000

Nitric oxide and atrial natriuretic factor stimulate cGMP-dependent membrane insertion of aquaporin 2 in renal epithelial cells.

In collecting duct principal cells, aquaporin 2 (AQP2) is shuttled from intracellular vesicles to the plasma membrane upon vasopressin (VP) stimulation. VP activates adenylyl cyclase, increases intracellular cAMP, activating protein kinase A (PKA) to phosphorylate AQP2 on the COOH-terminal residue, serine 256. Using rat kidney slices and LLC-PK1 cells stably expressing AQP2 (LLC-AQP2 cells), we now show that AQP2 trafficking can be stimulated by cAMP-independent pathways. In these systems, the nitric oxide (NO) donors sodium nitroprusside (SNP) and NONOate and the NO synthase substrate L-arginine mimicked the effect of VP, stimulating relocation of AQP2 from cytoplasmic vesicles to the plasma membrane. Unlike VP, these other agents did not increase intracellular cAMP. However, SNP increased intracellular cGMP, and exogenous cGMP stimulated AQP2-membrane insertion. Atrial natriuretic factor, which signals via cGMP, also stimulated AQP2 translocation. The VP and SNP effects were blocked by the kinase inhibitor H89. SNP did not stimulate membrane insertion of AQP2 in LLC-PK1 cells expressing the phosphorylation-deficient mutant 256SerAla-AQP2, indicating that phosphorylation of Ser256 is required for signaling. Both PKA and cGMP-dependent protein kinase G phosphorylated AQP2 on this COOH-terminal residue in vitro. These results demonstrate a novel, cAMP-independent and cGMP-dependent pathway for AQP2 membrane insertion in renal epithelial cells.

Amino Acid Sequence↗
PubMed2000

H(+)V-ATPase-dependent luminal acidification in the kidney collecting duct and the epididymis/vas deferens: vesicle recycling and transcytotic pathways.

Many vertebrate transporting epithelia contain characteristic 'mitochondria-rich' cells that express high levels of a vacuolar proton-pumping ATPase (H(+)V-ATPase) on their plasma membrane and on intracellular vesicles. In the kidney cortex, A-cells and B-cells are involved in proton secretion and bicarbonate secretion, respectively, in the distal nephron and collecting duct. A-cells have an H(+)V-ATPase on their apical plasma membrane and on intracellular vesicles, whereas the cellular location of the H(+)V-ATPase can be apical, basolateral, bipolar or diffuse in B-cells. The rat epididymis and vas deferens also contain a distinct population of H(+)V-ATPase-rich epithelial cells. These cells are involved in generating a low luminal pH, which is involved in sperm maturation and in maintaining sperm in an immotile state during their passage through the epididymis and vas deferens. In both kidney and reproductive tract, H(+)V-ATPase-rich cells have a high rate of apical membrane recycling. H(+)V-ATPase molecules are transported between the cell surface and the cytoplasm in vesicles that have a well-defined 'coat' structure formed of the peripheral V(1) subunits of the H(+)V-ATPase. In addition, we propose that B-type intercalated cells have a transcytotic pathway that enables them to shuttle H(+)V-ATPase molecules from apical to basolateral plasma membrane domains. This hypothesis is supported by data showing that A-cells and B-cells have different intracellular trafficking pathways for LGP120, a lysosomal glycoprotein. LGP120 was found both on the basolateral plasma membrane and in lysosomes in B-cells, whereas no LGP120 was detectable in the plasma membrane of A-cells. We propose that the 'polarity reversal' of the H(+)V-ATPase in B-intercalated cells is mediated by a physiologically regulated transcytotic pathway that may be similar to that existing in some other cell types.

Animals↗
PubMed2000

Biomedical research leaders: report on needs, opportunities, difficulties, education and training, and evaluation.

The National Association of Physicians for the Environment (NAPE) has assumed a leadership role in protecting environmental health in recent years. The Committee of Biomedical Research Leaders was convened at the recent NAPE Leadership Conference: Biomedical Research and the Environment held on 1--2 November 1999, at the National Institutes of Health, Bethesda, Maryland. This report summarizes the discussion of the committee and its recommendations. The charge to the committee was to raise and address issues that will promote and sustain environmental health, safety, and energy efficiency within the biomedical community. Leaders from every important research sector (industry laboratories, academic health centers and institutes, hospitals and care facilities, Federal laboratories, and community-based research facilities) were gathered in this committee to discuss issues relevant to promoting environmental health. The conference and this report focus on the themes of environmental stewardship, sustainable development and "best greening practices." Environmental stewardship, an emerging theme within and outside the biomedical community, symbolizes the effort to provide an integrated, synthesized, and concerted effort to protect the health of the environment in both the present and the future. The primary goal established by the committee is to promote environmentally responsible leadership in the biomedical research community. Key outcomes of the committee's discussion and deliberation were a) the need for a central organization to evaluate, promote, and oversee efforts in environmental stewardship; and b) immediate need to facilitate efficient information transfer relevant to protecting the global environment through a database/clearinghouse. Means to fulfill these needs are discussed in this report.

Biomedical Technology↗
PubMed2000

Fibre-reinforced materials.

This paper considers the role of fibres in the reinforcement of composite materials, and the significance of the form the fibre takes and the material from which it is made. The current dental applications of fibre reinforcement, including dental cements and splints, fibres made into structures for use in composites, denture bases and the contemporary use of fibres in fixed partial dentures, are reviewed. Their role in biomedical implants is surveyed and their future forecast.

Carbon↗
PubMed2000

A materials scientist's glimpse into the new millennium.

Questions about the materials which are in current use are posed and answered in this review, which speculates about the sort of dental materials we will be using, or would like to use in the next century. Consideration is given to the merits and failings of dental amalgam, composites and glass-ionomer cements prior to laying down the requirements of the ultimate direct filling material. The case for the continued use of dental alloys for large restorations is discussed and new ways of forming these are described. The use of many cunning techniques to improve the resistance of dental ceramics to catastrophic failure is reported and a general improvement in both the denture bases and orthodontic appliances of the future is predicted.

Acrylic Resins↗
PubMed2000

High-versus low-threshold surfactant retreatment for neonatal respiratory distress syndrome.

UNLABELLED: Surfactant therapy has become an effective standard therapy for infants with respiratory distress syndrome (RDS). The first dose may be given either as prophylaxis immediately after delivery, or as rescue after an infant has developed RDS. Second and subsequent doses are currently recommended by the manufacturers to be administered at minimal levels of respiratory support. PURPOSE: This study compared the relative efficacy of administering second and subsequent doses of Infasurf surfactant at a low threshold (FIO(2) >30%, still requiring endotracheal intubation) versus a high threshold (FIO(2) >40%, mean airway pressure >7 cm H(2)O) of respiratory support. METHODS: A total of 2484 neonates received a first dose of surfactant; 1267 reached conventional retreatment criteria and were randomized to be retreated according to low- or high-threshold criteria. They were then retreated at a minimum of 6-hour intervals each time they reached their assigned threshold until receiving a maximum of 4 total doses. Subjects were stratified by whether they received their first dose by prophylaxis or rescue and by whether their lung disease was considered complicated (evidence of perinatal compromise or sepsis) or uncomplicated. RESULTS: Among the patients randomized, 33% of prophylaxis and 23% of rescue subjects met criteria for the complicated stratum. Although infants allocated to the high-threshold strategy were receiving slightly more oxygen at 72 hours, there was no difference in the number receiving mechanical ventilation at 72 hours or in the secondary respiratory outcomes (requirement for supplemental oxygen or mechanical ventilation at 28 days, supplemental oxygen at 36 weeks' postconceptional age, inspired oxygen concentration >60% at any time). However, there was a significantly higher mortality for infants with complicated RDS who had received retreatment according to the high-threshold strategy. CONCLUSIONS: We conclude that equal efficacy can be realized by delaying surfactant retreatment of infants with uncomplicated RDS until they have reached a higher level of respiratory support than is the current standard. We speculate that this would result in a substantial cost-saving from less utilization of drug. Conversely, we believe that infants with complicated RDS should continue to be treated by the low-threshold retreatment strategy, which is currently recommended by the manufacturers of the commercially available surfactants.

Biological Products↗
PubMed2000

In colchicine-treated rats, cellular distribution of AQP-1 in convoluted and straight proximal tubule segments is differently affected.

In cells along the nephron, the recycling of various components between the plasma membrane and intracellular organelles by vesicle trafficking depends on intact microtubules (MT). Previous studies of rats treated with the MT-disrupting drug colchicine showed that some brush-border membrane (BBM) transporters in renal proximal convoluted tubule cells (PCTC) become internalized in numerous vesicles randomly scattered in the cytoplasm. In this study, we compare the intracellular distribution of MT and several BBM proteins [megalin, vacuolar (V)-ATPase, water channel aquaporin-1 (AQP-1)] as well as endocytosis of the in-vivo-injected fluorescent marker FITC-dextran in PCTC and proximal straight tubule cells (PSTC) in control and colchicine-treated rats. Immunoblotting and immunocytochemical data show that in the PCTC and PSTC colchicine treatment causes: (1) disappearance of MT, (2) strongly diminished endocytosis of FITC-dextran, and (3) marked loss of megalin and V-ATPase from the BBM and their redistribution into intracellular vesicles. Similar pattern was observed for the distribution of AQP-1 in the PCTC. However, in the PSTC, the staining intensity of AQP-1 in the BBM, as well as its intracellular distribution remained unaffected by colchicine treatment. We conclude that in the PSTC, either MT play a minor role in the recycling of AQP-1 between the BBM and intracellular vesicles or BBM AQP-1 turns over much more slowly than in the PCTC.

Animals↗
PubMed2000

Screening strategies for neonatal hearing loss: which test is best?

OBJECTIVE: The objective of this study was to evaluate the accuracy and cost effectiveness of three different methods of hearing screening in newborns. DESIGN: A prospective, randomized cohort design was used. One hundred and five newborns were tested in this preliminary study. SETTING: The study was conducted in a tertiary care hospital setting in both the well baby and special care nurseries. METHODS: Consenting subjects had their hearing tested using automated auditory brainstem response (AABR), distortion-product otoacoustic emissions, and click-evoked otoacoustic emissions. The time to perform the tests was recorded and the cost of each test was calculated. MAIN OUTCOME MEASURES: The main outcomes measured were the time taken to perform each test, the pass/fail rate for each test, and the estimated cost of the tests. RESULTS: In this small cohort of patients, we found that AABR was the most accurate test, but it took longer to perform and was more expensive than either of the otoacoustic emission tests. However, the sensitivity and specificity of otoacoustic emissions were less than that of AABR. Test time decreased as the examiner gained experience, and we anticipate that experience will also result in better accuracy for the otoacoustic emission tests. CONCLUSIONS: Hearing screening in a hospital-based newborn population is both feasible and cost effective. Although AABR was more expensive, its better accuracy must be considered. As technology improves, the cost of all three tests will diminish. More robust conclusions cannot be made based on this small patient population.

Canada↗
PubMed2000

Mechanism of capacitative Ca2+ entry (CCE): interaction between IP3 receptor and TRP links the internal calcium storage compartment to plasma membrane CCE channels.

Activation of cells by agents that stimulate inositol trisphoshate (IP3) formation causes, via IP3 receptor (IP3R) activation, the release of Ca2+ from internal stores and also the entry of Ca2+ via plasma membrane cation channels, referred to as capacitative Ca2+ entry or CCE channels. Trp proteins have been proposed to be the unitary subunits forming CCE channels; however, there is no definitive proof for this hypothesis. We have now identified amino acid sequences of a Trp and of an IP3R that interact to form stable complexes. These complexes appear to form in vivo, as evidenced by co-immunoprecipitation of Trp with IP3R and by the fact that expression of the respective interacting sequences modulates development of CCE brought about by store depletion. The finding that a Trp-interacting sequence of IP3R interferes with natural CCE leads us to conclude that Trp proteins are, indeed, structural members of CCE channels. We conclude further that direct coupling of IP3R to Trp is a physiological mechanism by which cells trigger CCE in response to signals that stimulate phosphoinositide hydrolysis and IP3 formation. Pros and cons of various CCE activation models are discussed.

Amino Acid Sequence↗
PubMed2000

Using the Internet for training.

An indisputable fact of life is that the Internet is changing the way business is done. The number of businesses that have web sites is growing at an incredible rate. Many of these supply training; online training offers numerous advantages over traditional training methods.

Audiovisual Aids↗
PubMed1999

Endothelial cell E- and P-selectin up-regulation in murine contact sensitivity is prolonged by distinct mechanisms occurring in sequence.

The selectins are adhesion molecules that mediate the tethering and rolling of leukocytes on vascular endothelium. Although E-selectin and P-selectin are known to be expressed by endothelial cells (EC) in response to proinflammatory stimuli, their pattern and mechanisms of expression in immune-mediated inflammation remain poorly understood. By quantifying luminal endothelial selectin expression via i.v. administration of radiolabeled mAb, we detected constitutive expression of P-selectin, but not E-selectin, in mouse skin. Both selectins were transiently up-regulated after intradermal TNF-alpha, IL-1alpha, or IL-1beta. In contrast, during a contact sensitivity response to oxazolone, expression of both selectins was prolonged, with distinct peaks at 6 and 48 h. Experiments with P-selectin gene-targeted mice showed that the P-selectin measured was exclusively expressed by EC rather than platelets. The early and late phases of selectin expression in contact sensitivity were differentiated in terms of their requirement for prior sensitization, and the action of IL-1. Whereas the early phase was a nonspecific 'irritant' response to oxazolone, the late phase was Ag specific and was partially IL-1 dependent. Therefore, persistence of both E- and P-selectin expression in vivo can occur as a result of sequential and distinct EC activation processes that appear to be at least partially different from those previously reported as stimulating ICAM-1 and VCAM-1 expression. The further elucidation of mechanisms of EC activation in this model may help determine the relative roles of selectins and ligands for leukocyte integrins in the sequential recruitment of T cells and other leukocyte subsets during ongoing immune-mediated inflammatory responses.

Animals↗
PubMed1999

Caveolin-2 localizes to the golgi complex but redistributes to plasma membrane, caveolae, and rafts when co-expressed with caveolin-1.

We have characterized comparatively the subcellular distributions of caveolins-1 and -2, their interactions and their roles in caveolar formation in polarized epithelial cells. In Fischer rat thyroid (FRT) cells, which express low levels of caveolin-2 and no caveolin-1, caveolin-2 localizes exclusively to the Golgi complex but is partially redistributed to the plasma membrane upon co-expression of caveolin-1 by transfection or by adenovirus-mediated transduction. In Madin-Darby canine kidney (MDCK) cells, which constitutively express both caveolin-1 and -2, caveolin-2 localized to both the Golgi complex and to the plasma membrane, where it co-distributed with caveolin-1 in flat patches and in caveolae. In FRT cells, endogenous or overexpressed caveolin-2 did not associate with low density Triton insoluble membranes that floated in sucrose density gradients but was recruited to these membranes when co-expressed together with caveolin-1. In MDCK cells, both caveolin-1 and caveolin-2 associated with low density Triton-insoluble membranes. In FRT cells, transfection of caveolin-1 promoted the assembly of plasma membrane caveolae that localized preferentially (over 99%) to the basolateral surface, like constitutive caveolae of MDCK cells. In contrast, as expected from its intracellular distribution, endogenous or overexpressed caveolin-2 did not promote the assembly of caveolae; rather, it appeared to promote the assembly of intracellular vesicles in the peri-Golgi area. The data reported here demonstrate that caveolin-1 and -2 have different and complementary subcellular localizations and functional properties in polarized epithelial cells and suggest that the two proteins co-operate to carry out specific as yet unknown tasks between the Golgi complex and the cell surface.

Animals↗
PubMed1999

The complete nucleotide sequence of chromosome 3 of Plasmodium falciparum.

Analysis of Plasmodium falciparum chromosome 3, and comparison with chromosome 2, highlights novel features of chromosome organization and gene structure. The sub-telomeric regions of chromosome 3 show a conserved order of features, including repetitive DNA sequences, members of multigene families involved in pathogenesis and antigenic variation, a number of conserved pseudogenes, and several genes of unknown function. A putative centromere has been identified that has a core region of about 2 kilobases with an extremely high (adenine + thymidine) composition and arrays of tandem repeats. We have predicted 215 protein-coding genes and two transfer RNA genes in the 1,060,106-base-pair chromosome sequence. The predicted protein-coding genes can be divided into three main classes: 52.6% are not spliced, 45.1% have a large exon with short additional 5' or 3' exons, and 2.3% have a multiple exon structure more typical of higher eukaryotes.

Animals↗
PubMed1999

Intraoperative 125I brachytherapy for high-risk stage I non-small cell lung carcinoma.

PURPOSE: Preliminary assessment of feasibility, efficacy, acute and chronic side effects associated with permanent intraoperative placement of 125I vicryl mesh brachytherapy in a select group of high-risk Stage I NSCLC who have undergone video-assisted thoracoscopic resection (VATR). METHODS AND MATERIALS: From January 8, 1997 to March 16, 1998, 23 patients with Stage I NSCLC at high risk for conventional surgery due to cardiopulmonary compromise underwent combined VATR and intraoperative placement of 125I seeds embedded in vicryl mesh. Seeds embedded in vicryl suture were attached with surgical clips to a sheet of vicryl mesh, and thoracoscopically inserted over the target area (tumor bed and staple line) with nonabsorbable suture or surgical clips. A total dose of 100-120 Gy prescribed to the periphery of the target area (defined as the staple line and tumor bed with a 1-cm margin) was delivered. RESULTS: The mean target area covered was 48 cm2 (range 40-72) and mean total activity was 22 mCi (range 17.2-28.2). The median length of postoperative stay was 7 days. The median follow-up was 11 months (range 2-20). Postoperative CT scans of the chest revealed no dislodgement of the seeds and no local recurrence in any patient. Three patients developed distant metastasis (1 died 6 months postoperatively; the other 2 are currently alive with disease). One patient developed an ipsilateral recurrence in the right lower lobe after having had a right upper lobe resection. There were 3 postoperative deaths due to medical comorbid conditions or surgical complications (1 in the immediate postoperative period). Pulmonary function testing performed 3 months after implantation revealed no significant difference between preoperative and postoperative values: mean preoperative FVC was 2.3 L (range 1.31-3.0) and postoperative FVC was 2.2 L (range 1.1-3.9), p = 0.42; mean preoperative FEV1 was 1.2 L (range 0.71-2.2), and postoperative FEV1 was 1.5 L (range 0.8-2.9), p = 0.28. CONCLUSION: Review of early data suggests that intraoperative 125I vicryl mesh brachytherapy in high-risk Stage I NSCLC is potentially effective and well tolerated, with no significant decline in measurable pulmonary function studies and no increase in postoperative complications. Longer follow-up is needed to determine ultimate local control and survival.

Aged↗
PubMed1999

Infectivity and cross-immunity studies of Theileria lestoquardi and Theileria annulata in sheep and cattle: I. In vivo responses.

In a series of experiments, sporozoite stabilates of a Theileria lestoquardi (Lahr) and a T. annulata (Ankara) stock prepared from Hyalomma anatolicum anatolicum ticks, were used to examine the infectivity of both parasite species for sheep and cattle and to study the development of cross-immunity between these parasite species. In the first experiment sheep and cattle were inoculated with T. lestoquardi sporozoites. Surviving animals and naive sheep and cattle were, in the second experiment, inoculated with T. annulata. In the third experiment, naive sheep and sheep previously infected with T. annulata, were inoculated with T. lestoquardi. The following responses to inoculations were monitored: clinical and haematological signs of infection, appearance of parasitic stages of the parasites in lymph node biopsies and in peripheral blood and serological response to T. lestoquardi and T. annulata schizont antigens. While T. lestoquardi readily infected sheep and caused severe disease, it did not infect cattle. On the other hand, T. annulata infected both cattle and sheep. However, whereas cattle became severely affected, infected sheep showed mild clinical symptoms only and piroplasms did not develop. Despite their different behaviour in the host species examined, cross-immunity studies suggested that the parasite species are very closely related. Experiments in sheep indicated that T. lestoquardi infection protected against subsequent T. annulata infection. On the other hand, recovery from T. annulata infection did not prevent infection by sporozoites of T. lestoquardi, resulting in the establishment of schizonts and their subsequent development into piroplasms, although it protected against the major clinical effects of T. lestoquardi infection.

Animals↗
PubMed1999

Infectivity and cross-immunity studies of Theileria lestoquardi and Theileria annulata in sheep and cattle: II. In vitro studies.

In the studies previously reported, the tick-borne protozoan parasites Theileria lestoquardi and Theileria annulata were shown to differ in their capacity to infect sheep and cattle. In the studies presented here, these findings were further supported. In vitro infectivity of T. lestoquardi and T. annulata sporozoites for peripheral blood mononuclear cells of sheep and cattle were determined by analysis of cell cultures for cell proliferation, the detection of parasites in Giemsa-stained cytospin smears and the establishment of continuously growing schizont-infected cell lines. In the same way, the development of schizont-infected cells into continuously growing cell lines was studied with material isolated ex vivo from the sheep and cattle undergoing primary infections described elsewhere. Comparisons were also made between development of ex vivo cell lines from animals undergoing primary infections with those of the animals undergoing challenge infection with the other parasite species. Theileria species specific primers were used in a PCR to determine the identity of the parasites in the cell lines. These in vitro studies confirmed earlier observations that T. lestoquardi was unable to infect cattle, whereas infection of all sheep with T. annulata was proven. Moreover, earlier indications of the development of partial cross-immunity in sheep of T. annulata to T. lestoquardi and vice versa were strengthened. These findings may thus have consequences for the understanding of the epidemiology of T. lestoquardi infections of sheep. On the other hand. since piroplasms were not demonstrated in sheep infected with T. annulata, such sheep will not be infective to ticks and will consequently be unlikely to play a role in the maintenance and transmission of T. annulata to cattle.

Animals↗