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D Liu

Publications and source records attributed to D Liu.

At least 703 records · Page 39Linked to original sources
PubMed1993

The ATP-binding component of a prokaryotic traffic ATPase is exposed to the periplasmic (external) surface.

The membrane-bound complex of bacterial periplasmic permeases consists of two hydrophobic integral membrane proteins and two copies of a hydrophilic ATP-binding protein. The ATP-binding proteins from all periplasmic permeases display a high level of sequence similarity and are referred to as "conserved components." The conserved component from the histidine permease, HisP, has been postulated on the basis of genetic evidence to be accessible at the exterior membrane surface, in contrast to the commonly postulated association with the interior membrane surface as peripheral membrane proteins. We have used proteolysis and biotinylation of membrane vesicles to show that HisP is accessible to these reagents at the external surface and that this orientation depends on the presence of the two hydrophobic components, HisQ and HisM. Several binding-protein-independent hisP mutants are shown to produce HisP proteins that are more susceptible to proteases from the external membrane surface. Since the hydrophilic component is well conserved also in a group of eukaryotic transporters, which together with many prokaryotic systems form the superfamily of traffic ATPases, this insight about its membrane topology has general implications for understanding the molecular mechanism of action of this large superfamily, which includes the cystic fibrosis transmembrane conductance regulator and multidrug-resistance proteins.

ATP-Binding Cassette Transporters↗
PubMed1993

Functional properties of retinal Müller cells following transplantation to the anterior eye chamber.

Two types of glial cells occur in the retina, Müller cells and astrocytes. These cells share several structural features such as extending endfeet onto blood vessels of the retina. Retinal vessels express a tight blood-retinal barrier which is comparable to the blood-brain barrier (BBB) of the CNS. While astrocytes have been implicated in the induction of the BBB, the role of Müller cells in the blood-retinal barrier is unknown. To determine if Müller cells are capable of influencing vascular permeability, we have prepared Müller cells that are free of astrocytes and transplanted them to a peripheral target, the anterior eye chamber. Müller cells were identified 2 weeks to 3 months after injection and were predominantly localized within the connective tissue of the ciliary body. The Müller cells occurred as dense clusters of cells closely associated with ciliary blood vessels. The ciliary vessels adjacent to Müller cells were freely permeable to circulating horseradish peroxidase (HRP), suggesting that Müller cells did not induce tight barrier properties from these leaky peripheral vessels. In contrast, cortical astrocytes injected into the anterior eye chamber preferentially formed a monolayer on the anterior surface of the iris, a region known to contain blood vessels that are impermeable to circulating tracers (e.g., Raviola, Exp Eye Res [Suppl] 25:27, 1977). Müller cells were rarely associated with the iris and the few cells that were present were located deep within the iris stroma rather than on the surface. The behaviour of guinea pig Müller cells transplanted to the anterior eye chamber contrasts sharply with that of cortical astrocytes in terms of: 1) the ocular compartment to which Müller cells migrate; 2) the tissue invasiveness of the cells; and 3) the degree of permeability of blood vessels adjacent to transplanted cells. The results of this study emphasize the functional distinctness of the two types of retinal glia and suggest that Müller cells from guinea pig retina may not be active in modifying the permeability properties of peripheral blood vessels, a function that has been suggested for astrocytes.

Animals↗
PubMed1993

Analysis of an osmotically regulated pathogenesis-related osmotin gene promoter.

Osmotin is a small (24 kDa), basic, pathogenesis-related protein, that accumulates during adaptation of tobacco (Nicotiana tabacum) cells to osmotic stress. There are more than 10 inducers that activate the osmotin gene in various plant tissues. The osmotin promoter contains several sequences bearing a high degree of similarity to ABRE, as-1 and E-8 cis element sequences. Gel retardation studies indicated the presence of at least two regions in the osmotin promoter that show specific interactions with nuclear factors isolated from cultured cells or leaves. The abundance of these binding factors increased in response to salt, ABA and ethylene. Nuclear factors protected a 35 bp sequence of the promoter from DNase I digestion. Different 5' deletions of the osmotin promoter cloned into a promoter-less GUSNOS plasmid (pBI 201) were used in transient expression studies with a Biolistic gun. The transient expression studies revealed the presence of three distinct regions in the osmotin promoter. The promoter sequence from -108 to -248 bp is absolutely required for reporter gene activity, followed by a long stretch (up to -1052) of enhancer-like sequence and then a sequence upstream of -1052, which appears to contain negative elements. The responses to ABA, ethylene, salt, desiccation and wounding appear to be associated with the -248 bp sequence of the promoter. This region also contains a putative ABRE (CACTGTG) core element. Activation of the osmotin gene by various inducers is discussed in view of antifungal activity of the osmotin protein.

Abscisic Acid↗
PubMed1993

Halide permeation through three types of epithelial anion channels after reconstitution into giant liposomes.

Anion-selective channels from apical membranes of cultured CFPAC-1 cells were isolated and incorporated into giant liposomes for patch clamp recording. Liposomes were formed from L-alpha-lecithin by a dehydration-hydration method. Ion channels were characterized using the excised inside-out patch clamp configuration. The most commonly observed anion channels were similar to those observed in native epithelial tissues. The linear 20 pS Cl- channel had the halide permeability sequence Cl- > I- > or = Br- > F-, and showed anomalous mole-fraction behavior in solutions containing different proportions of Cl- and F- ions. The autwardly rectifying Cl- channel had the halide permeability sequence I- > Br- > Cl- > F-, and also showed anomalous mole-fraction behavior, indicating that both these channels probably contain multi-ion pores. The third, voltage-dependent anion channel showed at least five different substrates, had a conductance of 390 pS in the main state, and showed two types of kinetics, fast (openings and closings < 1 ms), and slow (openings and closings > 1 s). The channel was seen more frequently after reconstitution into giant liposomes than in intact cells. It was not selective amongst the halides, and there was no deviation from a linear dependence of relative current on molar fractions, indicating relatively simple permeation through the pore. Differences in halide permeabilities suggest that different anion channels may be related to different membrane proteins. Comparison with the chloride channel proteins isolated biochemically from epithelial cell membranes is discussed.

Cell Membrane Permeability↗
PubMed1993

Analysis of taeniid antigens using monoclonal antibodies to Echinococcus granulosus antigen 5 and antigen B.

Antigens derived from Echinococcus granulosus, Taenia hydatigena and T. pisiformis cyst fluids, T. solium cysticerci, E. multilocularis protoscoleces and E. vogeli cyst membranes were examined by enzyme-linked immunosorbent assay (ELISA) and immunoelectrophoresis (IEP) using four monoclonal antibodies (mAb) to E. granulosus antigen 5 (Ag5) and antigen B (AgB). Anti-Ag5 mAbs 24.14 and 61A12 reacted strongly with T. hydatigena and T. pisiformis cyst fluids and, to a lesser degree, anti-AgB MAbs 31.15 and 39B3 also displayed some reaction with these antigens in ELISA. The formation of a modified arc 5 band between Anti-Ag5 mAbs and T. hydatigena cyst fluid (THCF) in IEP further confirms the existence of Ag5 in T. hydatigena cyst fluid. However, the inability of THCF and T. pisiformis cyst fluid (TPCF) to form an AgB band as well as that of TPCF to form an arc 5 band with mAbs in IEP does not exclusively prove the lack of AgB in THCF and TPCF or the lack of Ag5 in TPCF. The absence of a reaction of mAbs with T. solium, E. multilocularis and E. vogeli antigen preparations in ELISA or IEP would suggest that these mAbs may recognise epitopes different from those of T. solium, E. multilocularis and E. vogeli parasites; this might be exploited for specific differentiation of E. granulosus.

Animals↗
PubMed1993

Using an integrated software package for clinical data analysis on a microcomputer.

An integrated software package was used effectively for entering, organizing and analyzing clinical research data on a microcomputer. Both the database and the spreadsheet components of the package were used in the process. The database component enabled a form to be created for entering the data. The spreadsheet component was used in the organization and analysis of data. Macros were written within the spreadsheet environment for the statistical analysis of data. The purpose of this paper is to illustrate how an integrated software like Symphony could offer features beyond simply the use of a spreadsheet for the analysis of research data. Also highlighted are the other useful features of the integrated software that are not directly related to data analysis.

Adolescent↗
PubMed1993

Calcium dependent magnesium uptake in myocardium.

The frog myocardium maintains magnesium content at a steady state level when stimulated at 0.4Hz while being perfused with Ringer's solution containing 1 x 10(-3) M Ca2+ and 5 x 10(-7) M magnesium. When calcium is removed 43% of tissue magnesium is lost within 30 seconds or 12 beats. Restoration of calcium to the perfusion solution causes reaccumulation of magnesium from a solution containing 5 x 10(-7) M magnesium. The reaccumulation of magnesium indicates a highly selective transport system for magnesium which is dependent upon the presence of calcium. Calcium appears to reduce the leak of magnesium from the myocardium and enhances the transport of magnesium into the myocardial cell. Intracellular magnesium is a necessary cofactor for hundreds of enzymes, and is essential for protein synthesis and as an extracellular divalent cation helps to stabilize excitable membranes in conjunction with calcium. The concentration of ionized magnesium in the sarcoplasm of myocardial muscle has an average value of 1.45 mM +/- 1.37 (standard deviation), N = 19) with a range of 0.5 to 3.6 mM (1). The heart with its numerous mitochondria and high enzymatic activity is vulnerable to myocardial damage due to magnesium loss. The isolated frog ventricle conserves intracellular magnesium when perfused with Ringer's solution containing no added magnesium and maintains function for hours. The ability to conserve magnesium suggests a low permeability of the sarcolemma to magnesium and an extremely efficient inward transport system. Removal of calcium as well as magnesium from the perfusion solution causes a rapid loss of tension in the electrically driven frog ventricle (0.4) Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1993

Use of elastase test, gelatin gel test and electrophoretic zymogram to determine virulence of Dichelobacter nodosus isolated from ovine foot rot.

A comparative study using the elastase test, gelatin gel test and electrophoretic zymogram was conducted for virulence determination of 96 Dichelobacter nodosus isolates from clinical cases of ovine foot rot. Despite being time consuming, the elastase test provided a classification of D nodosus bacteria in general agreement with the severity of clinical characteristics. The gelatin gel test showed some correlation with the elastase test. While isolates showing elastase activity at 14 days or less were likely to produce more proteases which were of higher thermostability, those showing elastase activity at 21 to 28 days, or elastase negative up to 28 days tended to produce less proteases which were also of lower thermostability. The electrophoretic zymogram based on the virulent pattern 1 (V1), virulent pattern 2 (V2) and benign pattern (B) did not cover all isolates from the field as nine (9.4 per cent) of the 96 isolates formed specific isoenzyme patterns that were different from the V1, V2 and B patterns of classification. However, the patterns formed by these nine isolates could be fitted into another previously reported isoenzyme classification. Nevertheless, the electrophoretic zymogram by itself did not provide adequate information in regard to intermediate foot rot. It appeared that a combination of two tests such as elastase test and zymogram or gelatin gel test and zymogram would offer a useful complementary definition of the virulence of D nodosus bacteria.

Animals↗
PubMed1993

Generation and detection of hydroxyl radical in vivo in rat spinal cord by microdialysis administration of Fenton's reagents and microdialysis sampling.

We developed a double microdialysis fiber technique to generate hydroxyl radicals (OH.) in rat spinal cord. H2O2 and FeCl2/EDTA were pumped through two parallel microdialysis fibers inserted into the spinal cord such that the reactants mix in the tissue to generate OH. by the Fenton reaction. Generated OH. was detected by administering phenylalanine through one fiber and measuring o-, m- and p-hydroxyphenylalanine in collected dialysates by high pressure liquid chromatography and fluorescence detection. The hydroxyphenylalanines are produced by OH. attacking the phenylalanine. OH. generation was also accomplished in in vitro experiments and the results were consistent with in vivo experiments. This novel method to generate and measure OH. radical in vivo overcomes difficulties in studying damage to tissue by short-lived OH.. Although developed to study the role of OH. in spinal cord injury, this method could be used to study other diseases involving OH. damage.

Animals↗
PubMed1993

Effects of aluminium ion on root growth, cell division, and nucleoli of garlic (Allium sativum L.).

The effects of different concentrations of aluminium chloride on root growth, cell division, chromosome morphology and nucleoli in root tip cells of garlic (Allium sativum L.) were studied. The concentrations of aluminium chloride (AlCl(3)) used were 10(-5), 10(-4), 10(-3), 10(-2) and 10(-1) m. Aluminium chloride inhibited root growth and caused mitotic irregularities, including c-mitosis, anaphase bridges, and chromosome stickiness. Nucleolar material was extruded from the nucleus into the cytoplasm. Extrusion was observed in inner root meristem and root cap cells. The poisoning by Al(3+) of the root tip cells of Allium sativum may result from the uptake and accumulation of Al and inhibition of Ca uptake, distribution of physiological activities of calmodulin (CaM) and the inhibition of some enzyme reactions.

Journal Article↗
PubMed1993

Dichelobacter nodosus: differentiation of virulent and benign strains by gene probe based dot blot hybridisation.

Gene probes specific for benign and virulent strains of Dichelobacter nodosus were used in a dot blot hybridisation procedure involving 96 strains of D. nodosus isolated from cases of ovine footrot. The performance of the probes was compared with that of the elastase test. All 27 strains with elastase activity at 7 days and 12 of 25 strains with elastase activity at 14 days reacted with the virulent-specific probe. Twenty-four strains with elastase activity between 21-28 days, and 20 strains with negative elastase activity up to 28 days did not bind with this probe. On the other hand, the benign-specific probe failed to bind with the 27 strains with elastase activity at 7 days, and 13 of the 25 strains with elastase activity at 14 days but reacted with 20 of the 24 strains with elastase activity at 21-28 days, and 19 of the 20 strains with negative elastase activity up to 28 days. The 12 strains with elastase activity at 14 days which were detected by the virulent-specific probe were not those recognised by the benign-specific probe. The use of virulent and benign specific gene probes in combination provides a rapid and precise screening system for differentiation of virulent and higher intermediate footrot from benign and lower intermediate footrot.

Animals↗
PubMed1993

Polymer membrane-based ion-, gas- and bio-selective potentiometric sensors.

Recent progress in the design of new polymer membrane-based potentiometric ion-, gas- and bio-selective electrodes in chemistry laboratories at the University of Michigan (Ann Arbor) is reviewed. Emphasis is placed on describing the performance of devices for measuring anions (e.g., salicylate, thiocyanate, chloride and heparin) and gases (e.g., ammonia, carbon dioxide and oxygen) in biological samples, both in vitro and in vivo. Beyond direct measurement of key ions and gases in complex matrices, some of the new membrane electrode systems reported can serve as base transducers for the development of biosensors containing integrated biological reagents, including enzymes and antibodies. New approaches for mass fabricating solid-state ion and biosensor devices as well as future directions for research in the entire field of polymer membrane sensors are also described.

Anions↗
PubMed1993

Ptosis repair by single suture aponeurotic tuck. Surgical technique and long-term results.

PURPOSE: To assess the effectiveness and long-term results of a simplified aponeurotic tuck technique for ptosis repair. METHODS: The author simplified the aponeurotic approach for ptosis repair by minimizing the dissection and using a single 6-0 nylon stitch to control the lid height and curvature. Prospectively, 169 ptotic lids were repaired by this technique over a 7-year period. All consecutive patients with ptosis ranging from 1 to 5 mm, levator function greater than 8 mm, and with no history of previous eyelid surgery were included. Patients with measurements and levator function outside of this range or who had ptosis secondary to eyelid or orbital mass, as a complication of eyelid surgery, or associated with systemic disease were excluded. The follow-up period ranged from 18 to 96 months, with an average of 60 months. RESULTS: Of the 169 eyelids, 162 (95%) were corrected to 1 mm. There were 12 reoperations, including 4 on patients who had initial correction to within 1 mm. Complications included overcorrection in three patients and undercorrection in six, peaking in five, and two immediate recurrences and three late recurrences. Long-term results were excellent, as no change in the lid height was observed. CONCLUSION: The single-stitch aponeurotic tuck is simple, effective, and versatile. It can be used in the correction of involutional, postcataract, traumatic, and congenital types of ptosis. Although local anesthesia is preferred, consistent results also can be obtained in those cases where general anesthesia is indicated. The complications that occurred were minimal and easily corrected.

Adolescent↗
PubMed1993

Assessment of monoclonal antibodies to Echinococcus granulosus antigen 5 and antigen B for detection of human hydatid circulating antigens.

Four monoclonal antibodies (MAb) to Echinococcus granulosus Antigen 5 (Ag5) and Antigen B (AgB) were assessed in an enzyme-linked immunosorbent assay (ELISA) for detection of circulating antigens (CAg) in sera of human patients with E. granulosus infection. Around 5.5-8% of 200 sera from 42 surgically proven hydatid patients contained detectable CAg by individual MAb. The combined detection rate for CAg, using four MAb, was 19% (38/200). Although hydatid CAg was detected by MAb in at least one serum sample from 21 of 42 patients, some patients remained negative in the assay regardless of the time when serum samples were taken (pre- or post-operatively), or of the continuing presence of hydatid cysts, their location or fertility. In addition, it was observed that the binding capacity of MAb for sheep hydatid cyst fluid antigen (SHCF) was somewhat reduced in the presence of normal human serum. The CAg detection assay would only be useful for assessment of hydatid infection status in patients with detectable CAg in serum samples.

Acids↗
PubMed1993

Dipstick dot ELISA for the detection of Taenia coproantigens in humans.

A dipstick dot ELISA for detection of Taenia-specific coproantigens was developed. The test was based on a sandwich ELISA using antibodies raised against adult Taenia solium. Antibodies were absorbed to nitrocellulose paper previously adhered to acetate plastic to form dipsticks. Once blocked with 5% skimmed milk and dried the antibody-coated dipsticks were stable for several weeks at room temperature. Both micro and dot ELISA formats were genus specific although the dot ELISA was less sensitive than the micro ELISA based on the same antiserum. During field studies, in which the majority of samples were tested in rural villages soon after collection, 3728 samples were tested. All samples were also examined by microscopy using formol ether concentration and individuals questioned to determine whether they were aware of being infected. After the initial diagnostic work individuals were treated with taeniacidal drugs for worm recovery. Use of the coproantigen test significantly increased the number of cases diagnosed. Of the 41 cases diagnosed by the three diagnostic techniques combined 31 were detected by the dipstick assay making it the most sensitive technique employed. The specificity of the dipstick assay was 99.9% with a positive predictive value of 88.6%. The combined diagnostic approach did not, however, diagnose all cases. The coproantigen test was fast and easy to use. Further improvements may make the dipstick test suitable for wide-scale use in field studies and diagnostic laboratories.

Antigens, Helminth↗
PubMed1993

Loss of cell-cell and cell-matrix adhesion molecules in colorectal cancer.

Adhesion molecules are thought to play a vital role in the induction and maintenance of tissue differentiation and their loss or down-regulation has been implicated in the neoplastic process. Recent studies have shown that the morphoregulatory activities are a consequence of interactive processes between several cell adhesion molecules rather than the function of a single molecule. Therefore, we have investigated a panel of adhesion molecules including members of the integrin, cadherin and immunoglobin superfamily in colorectal cancer. Twenty-eight consecutive colorectal adenocarcinomas were stained using an avidin-biotin indirect immunoperoxidase technique. Our results showed a consistent loss of the alpha 2 and beta 1 integrin subunits (21/28 = 75% and 22/28 = 78.6% respectively) and a decrease in expression of E-cadherin in 5/5 poorly differentiated adenocarcinomas. Carcinoembryonic antigen expression was preserved but with basolateral accentuation seen in tumours. There was no statistical correlation with Dukes' stage. These results provide further evidence that in colorectal cancer there is a widespread deregulated expression of cell-cell and cell-matrix adhesion molecules. Changes in the expression and function of adhesion molecules which regulate growth and differentiation may play a role in the behaviour of colorectal cancer.

Adenocarcinoma↗
PubMed1993

An experimental model combining microdialysis with electrophysiology, histology, and neurochemistry for exploring mechanisms of secondary damage in spinal cord injury: effects of potassium.

An experimental model for characterizing effects of agents suspected to cause damage secondary to spinal cord injury is presented. Microdialysis was used to administer candidate damaging agents and to sample the release of other substances in response to administered agents. Damage was assessed by monitoring the amplitudes of evoked potentials during candidate administration and by postmortem histologic examination. This approach enabled the correlation of electrophysiologic, histologic, and neurochemical parameters in the same experiment. Potassium was chosen as a candidate damaging agent, because (1) in high extracellular concentrations it destroys neurons and (2) its extracellular concentration rises substantially following impact injury to the spinal cord. A technique using parallel administering and collecting microdialysis fibers was developed to estimate the in vivo concentration of K+ outside the administering fiber. Administration of 100 mM KCl, 50 mM K2HPO4, or 100 mM potassium glucuronate in artificial cerebrospinal fluid blocked electrical conduction and destroyed cell bodies. Release of the neurotransmitter amino acids aspartate, glutamate, glycine, and gamma-aminobutyric acid (GABA) and the possible neurotransmitter taurine were dramatically increased by administration of 100 mM KCl. Levels of non-neurotransmitter amino acids increased to lesser degrees. Impairment of conduction, destruction of cell bodies, and release of excitotoxins were all consistent with elevated K+ serving as a secondary damaging agent in spinal cord injury.

Amino Acids↗