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Biomedical subjects

X Gu

Publications and source records attributed to X Gu.

At least 19 recordsLinked to original sources
PubMed1997

Transvenous closure of secundum atrial septal defects: preliminary results with a new self-expanding nitinol prosthesis in a swine model.

BACKGROUND: Our purpose was to evaluate a new prosthesis for percutaneous closure of secundum atrial septal defects (ASDs). METHODS AND RESULTS: Percutaneous closure of surgically created fossa ovalis ASD was attempted in 15 minipigs. The mean balloon-stretched ASD diameter was 12.3+/-2.3 mm (range, 10 to 16 mm). The self-expanding prosthesis was braided from 0.005-in Nitinol wires in the shape of two flat buttons with a short connecting waist with a diameter corresponding to that of the defect to be closed. Polyester filling was added to enhance thrombogenicity. Pulmonary arteriography with levo-phase was obtained before placement; immediately after placement; and at 1-week, 1-month, and 3-month follow-ups. Four animals were killed at 1 week, 1 month, and 3 months for histopathological correlation. Three deaths resulted from ventricular fibrillation (one during anesthesia and two during the placement procedure). Successful placement of the prosthesis was achieved in the remaining 12 animals. Overall immediate ASD closure on angiography occurred in 7 of 12 animals (all polyester-filled prostheses). Absent or trace shunt by angiography was present in 11 of 12 devices at 1 week, with the remaining one demonstrating a small shunt. All septal defects were completely closed at 1 month with the exception of one case in which delayed partial dislodgment of an undersized prosthesis into the right atrium had developed. Closure rate at 3 months was 100%. Neoendothelialization and fibrous incorporation of the prosthesis were completed within 1 to 3 months. CONCLUSIONS: Effective and permanent occlusion of secundum ASDs is feasible with a device that offers the advantages of easy placement, self-centering, and repositionability.

Alloys↗
PubMed1997

Sex differences in mutation rate in higher primates estimated from AMG intron sequences.

To study sex differences in mutation rate in primates, we sequenced the third introns of the AMGX and AMGY genes from humans, orangutans, and squirrel monkeys and estimated that the male-to-female ratio of mutation rate is alpha = 5.14 with the 95% confidence interval (2.42, 16.6). Combining this data set and the data sets from ZFX/ZFY and SMCX/SMCY introns, we obtained an estimate of alpha = 5.06 with the 95% confidence interval reduced to (3.24, 8.79). The alpha value is significantly higher in higher primates than in rodents.

Animals↗
PubMed1997

Dynamics of phragmoplastin in living cells during cell plate formation and uncoupling of cell elongation from the plane of cell division.

The cell plate is formed by the fusion of Golgi apparatus-derived vesicles in the center of the phragmoplast during cytokinesis in plant cells. A dynamin-like protein, phragmoplastin, has been isolated and shown to be associated with cell plate formation in soybean by using immunocytochemistry. In this article, we demonstrate that similar to dynamin, phragmoplastin polymerizes to form oligomers. We fused soybean phragmoplastin with the green fluorescence protein (GFP) and introduced it into tobacco BY-2 cells to monitor the dynamics of early events in cell plate formation. We demonstrate that the chimeric protein is functional and targeted to the cell plate during cytokinesis in transgenic cells. GFP-phragmoplastin was found to appear first in the center of the forming cell plate, and as the cell plate grew outward, it redistributed to the growing margins of the cell plate. The redistribution of phragmoplastin may require microtubule reorganization because the microtubule-stabilizing drug taxol inhibited phragmoplastin redistribution. Our data show that throughout the entire process of cytokinesis, phragmoplastin is concentrated in the area in which membrane fusion is active, suggesting that phragmoplastin participates in an early membrane fusion event during cell plate formation. Based on the dynamics of GFP-phragmoplastin, it appears that the process of cell plate formation is completed in two phases. The first phase is confined to the cylinder of the phragmoplast proper and is followed by a second phase that deposits phragmoplast vesicles in a concentric fashion, resulting in a ring of fluorescence, with the concentration of vesicles being higher at the periphery. In addition, overexpression of GFP-phragmoplastin appears to act as a dominant negative, slowing down the completion of cell plate formation, and often results in an oblique cell plate. The latter appears to uncouple cell elongation from the plane of cell division, forming twisted and elongated cells with longitudinal cell divisions.

Antibodies↗
PubMed1997

Breaking the code: regulation of neuronal differentiation by spontaneous calcium transients.

Calcium ions play critical roles in neuronal development. Stimulation of transient elevations of intracellular calcium (Ca2+i) activates protein kinases, regulates transcription and influences motility and morphology. Embryonic Xenopus spinal neurons exhibit a Ca(2+)-sensitive period in culture; removing extracellular Ca2+ during this period affects several aspects of neuronal differentiation. However, both the mechanisms that generate natural fluctuations in Ca2+i and the signals they transduce are not well understood. Spontaneous, transient and repeated elevations of Ca2+i in embryonic Xenopus spinal neurons have been observed over periods up to 5 h in vitro and in vivo, confocally imaging fluo 3-loaded cells. Developing neurons generate two distinctive types of spontaneous Ca2+i transients, calcium spikes and calcium waves. We have investigated the mechanisms by which they are generated and their roles in directing neuronal differentiation. Spikes are generated by spontaneous action potentials, and thus are rapidly propagated throughout entire neurons. Ca2+ entry triggers Ca2+ release from intracellular stores, and spikes have a characteristic double exponential decay. In contrast, the generation of waves does not involve conventional voltage-dependent Ca2+ channels, but an unknown Ca2+ entry pathway that can be blocked by Ni2+ at a higher concentration than required to block classical voltage-dependent Ca2+ channels. Waves rise and decay slowly, and unlike spikes, are local events. However both spikes and waves are abolished by removal of extracellular Ca2+. Developmentally, the incidence and frequency of spikes decrease while the incidence and frequency of waves are constant. To study the roles of Ca2+ transients, we have imaged Ca2+ in spinal neurons throughout an extended period of early development, and find that spikes and waves are expressed at distinct frequencies. Neuronal differentiation is altered when they are eliminated by preventing Ca2+ influx. By reimposing different frequency patterns of Ca2+ transients, we demonstrate that natural spike activity is sufficient to promote normal neurotransmitter expression and channel maturation, while wave activity at growth cones is sufficient to regulate neurite extension. On the other hand, suppression of spontaneous Ca2+ elevations with BAPTA, a rapid Ca2+ chelator, indicates that they are also necessary to direct differentiation. Ca2+ transients appear to encode information in their frequency. Thus, they act like action potentials, although they are 10(4) times longer in duration and less frequent and implement an intrinsic development program.

Animals↗
PubMed1996

3' Processing and termination of mouse histone transcripts synthesized in vitro by RNA polymerase II.

The highly expressed mouse histone H2a-614 gene is located 800 nt 5' of the histone H3-614 gene. There is a 140 nt sequence located 500 nt from the end of the H2-614 mRNA which has been defined as a transcription termination site for RNA polymerase II. We established an in vitro transcription system in which both 3' end processing and transcription termination occur. A template containing the adenovirus major late promoter, a portion of the histone H2a-614 coding region, its 3' processing signal, followed by the transcription termination site was transcribed in a nuclear extract prepared from mouse myeloma cells. Some of the transcripts synthesized in the extract were cleaved at the histone processing site in a reaction which was dependent both on the hairpin binding factor and the U7 snRNP. The efficiency of histone 3' end formation was similar both on synthetic transcripts and transcripts synthesized by RNA polymerase II. Defined transcripts, which were not processed and which mapped to the transcription termination site, were released from the template, suggesting that they were formed by transcription termination. Termination in vitro was dependent on a functional histone processing signal.

Animals↗
PubMed1996

Recognition of the T-arm of tRNA by tRNA (m5U54)-methyltransferase is not sequence specific.

tRNA (m5U54)-methyltransferase (RUMT) catalyzes the methylation of U54 of tRNAs. In contrast to enzymes which recognize a particular tRNA, RUMT recognizes features common to all tRNAs. We have shown that these features reside in the T-arm of tRNA and constructed a minimal consensus sequence for RUMT recognition and catalysis (Gu et al., 1991b). Here, we have mutated each conserved T-loop residue and conserved T-stem base pair to bases or base pairs which are not observed in Escherichia coli tRNA. The substrate specificity of RUMT for 30 in vitro synthesized T-arm mutants of tRNAPhe and 37 mutants of the 17-mer analog of the T-arm derived from tRNA1Val was investigated. A 2-5 base pair stem was essential for recognition of the T-arm by RUMT, but the base composition of the stem was unimportant. The 7-base size of the T-loop maintained by the stem was essential for RUMT recognition. For tRNA, most base substitutions in the 7-base loop did not eliminate RUMT activity, except for any mutation of the methyl acceptor U54 and the C56G mutation. The effect of base and base pair mutations on Kcat or the rate of methylation by RUMT was more striking than the effect on the Kd for binding to RUMT. In comparison with mutations in the T-loop of intact tRNA, base mutation in the T-loop of the 17-mer T-arm had a more deleterious effect on binding and methylation. Surprisingly, recognition of tRNA by RUMT appears to reside in the three-dimensional structure of the seven-member T-loop rather than in its primary structure.

Base Sequence↗
PubMed1996

Modulation of honey bee thermoregulation by adrenergic compounds.

The effects of adrenergic compounds on the thermoregulation of resting honey bees were investigated using a non-traumatizing approach. Bees fed ad lib were treated orally and kept at an ambient temperature of 22 degrees C; the surface thoracic temperature was monitored by infrared thermography. Bees were treated with the adrenergic agonists epinephrine and ephedrine, and with the beta-blocking agent alprenolol. Low doses of adrenergic agonists had no significant effect on thermogenesis, but high doses caused a hypothermia. Alprenolol triggered a dose-dependent hypothermia that was reversed by low doses of epinephrine and ephedrine. Results are discussed with reference to the metabolic and neural adrenergic pathways that may be involved in bee thermoregulation.

Alprenolol↗
PubMed1996

A general additive distance with time-reversibility and rate variation among nucleotide sites.

As additivity is a very useful property for a distance measure, a general additive distance is proposed under the stationary time-reversible (SR) model of nucleotide substitution or, more generally, under the stationary, time-reversible, and rate variable (SRV) model, which allows rate variation among nucleotide sites. A method for estimating the mean distance and the sampling variance is developed. In addition, a method is developed for estimating the variance-covariance matrix of distances, which is useful for the statistical test of phylogenies and molecular clocks. Computer simulation shows (i) if the sequences are longer than, say, 1000 bp, the SR method is preferable to simpler methods; (ii) the SR method is robust against deviations from time-reversibility; (iii) when the rate varies among sites, the SRV method is much better than the SR method because the distance is seriously underestimated by the SR method; and (iv) our method for estimating the sampling variance is accurate for sequences longer than 500 bp. Finally, a test is constructed for testing whether DNA evolution follows a general Markovian model.

Analysis of Variance↗
PubMed1996

Rapid monitoring of site-specific glycosylation microheterogeneity of recombinant human interferon-gamma.

An analytical system is presented for rapid assessment of site-specific microheterogeneity of the two potential N-linked glycosylation sites of recombinant human interferon-gamma (IFN-gamma) derived from Chinese hamster ovary cell culture. The target protein is first purified from culture supernatant by immunoaffinity chromatography, and the acidic eluent is neutralized via an in-line mixing tee. On-line proteolysis is rapidly performed by an immobilized trypsin cartridge, and reversed-phase chromatography isolates the two pools of glycopeptides representing the potential glycosylation sites. Following off-line analysis by matrix-assisted laser-desorption ionization/time-of-flight (MALDI/TOF) mass spectrometry, observed mass shifts of glycopeptides relative to the known masses of their amino acid portions are correlated to site-specific oligosaccharide structures. Desialylation of glycopeptides by sialidase treatment on the MALDI sample plate allows for quantitative estimations of asialoglycan structures by MALDI/TOF. This methodology permits glycoprotein microheterogeneity to be evaluated in a time frame of approximately 2 h, utilizing as little as 0.5 microgram (25 pmol) of product. Results of monitoring a batch culture are presented as well as analysis of a culture containing deoxymannojirimycin, an inhibitor of glycoprotein processing.

1-Deoxynojirimycin↗
PubMed1996

Interaction of tRNA (uracil-5-)-methyltransferase with NO2Ura-tRNA.

tRNA in which uracil is completely replaced by 5-nitro-uracil was prepared by substituting 5-nitro-UTP for UTP in an in vitro transcription reaction. The rationale was that the 5-nitro substituent activates the 6-carbon of the Ura heterocycle towards nucleophiles, and hence could provide mechanism-based inhibitors of enzymes which utilize this feature in their catalytic mechanism. When assayed shortly after mixing, the tRNA analog, NO2Ura-tRNA, is a potent competitive inhibitor of tRNA-Ura methyl transferase (RUMT). Upon incubation, the analog causes a time-dependent inactivation of RUMT which could be reversed by dilution into a large excess of tRNA substrate. Covalent RUMT-NO2Ura-tRNA complexes could be isolated on nitrocellulose filters or by SDS-PAGE. The interaction of RUMT and NO2Ura-tRNA was deduced to involve formation of a reversible complex, followed by formation of a reversible covalent complex in which Cys 324 of RUMT is linked to the 6-position of NO2Ura 54 in NO2Ura-tRNA.

Binding Sites↗
PubMed1996

Phragmoplastin, a dynamin-like protein associated with cell plate formation in plants.

Cytokinesis in a plant cell is accomplished by the formation of a cell plate in the center of the phragmoplast. Little is known of the molecular events associated with this process. In this study, we report the identification of a dynamin-like protein from soybean and demonstrate that this protein is associated with the formation of the cell plate. Plant dynamin-like (PDL) protein contains 610 amino acids showing high homology with other members of the dynamin protein family. Western blot experiments demonstrated that it is associated with the non-ionic detergent-resistant fraction of membranes. Indirect immunofluorescence microscopy localized PDL to the cell plate in dividing soybean root tip cells. Double labeling experiments demonstrated that, unlike phragmoplast microtubules which are concentrated on the periphery of the forming plate, PDL is located across the whole width of the newly formed cell plate. Based on the temporal and spatial organization of PDL in the phragmoplast, we termed this protein 'phragmoplastin'. The data suggest that phragmoplastin may be associated with exocytic vesicles that are depositing cell plate material during cytokinesis in the plant cell.

Amino Acid Sequence↗
PubMed1996

The crystal structure of a high oxygen affinity species of haemoglobin (bar-headed goose haemoglobin in the oxy form).

We have determined the crystal structure of bar-headed goose haemoglobin in the oxy form to a resolution of 2.0 A. The R-factor of the model is 19.8%. The structure is similar to human HbA, but contacts between the subunits show slightly altered packing of the tetramer. Bar-headed goose blood shows a greatly elevated oxygen affinity compared to closely related species of geese. This is apparently due to a single proline to alanine mutation at the alpha 1 beta 1 interface which destabilises the T state of the protein. The beta chain N and C termini are well-localized, and together with other neighbouring basic groups they form a strongly positively charged groove at the entrance to the central cavity around the molecular dyad. The well-ordered conformation and the three-dimensional distribution of positive charges clearly indicate this area to be the inositol pentaphosphate binding site of bird haemoglobins.

2,3-Diphosphoglycerate↗
PubMed1996

Isolation of the C9b fragment of human complement component C9 using urea in the absence of detergents.

The bactericidal activity of the C5b-9 complex of complement is dependent upon the terminal complement component C9. The precursor C5b-8 complex is not harmful to bacterial cells until C9 is added to complete the C5b-9 complex. The C9 molecule can be proteolytically cleaved by thrombin to yield an intact, nicked molecule that remains fully functional when added to either bacterial cells or erythrocytes bearing pre-formed C5b-8 complexes. In investigating the membranolytic function of C9 in the C5b-9 complex, the carboxyl-terminal portion of the nicked molecule (C9b) has been shown to be membranolytic when added to erythrocytes, liposomes, or bacterial inner membranes in the absence of any other complement components. The isolation of C9b from nicked C9 has been accomplished by preparative gel electrophoresis using detergents, however the study of the activity of C9b in membrane systems may be complicated by the possible presence of residual detergent. To address this concern, we have used 4 M urea in conjunction with hydroxyapatite chromatography and a phosphate elution procedure to separate the domains of nicked C9. The isolated C9b domain, free of detergents and in the absence of any other complement components, was found to be membranolytic. C9b isolated in this manner was capable of lysing erythrocytes and inhibiting the growth of bacterial spheroplasts.

Complement C9↗
PubMed1996

Enalaprilat, an angiotensin-converting enzyme inhibitor, enhances functional preservation during long-term cardiac preservation. Possible involvement of bradykinin and PKC.

We investigated the effect of enalaprilat (ET) on long-term preservation of cardiac explant. Isolated rat hearts (n = 7/group) were pretreated with 0 to 40 nM ET and stored at 0 degree C for 16 h. Functional viability was assessed after 30-min working reperfusion without ET. Prestorage control function (mean +/- S.E.M.) (n = 7) included heart rate (HR), 291 +/- 12 bpm; aortic flow (AF). 49.8 +/- 1.9 ml/min; coronary flow (CF), 25.2 +/- 1.3 ml/min; cardiac output (CO), 75.0 +/- 1.2 ml/min; and work, 89.4 +/- 4.7 g-m/min. Post-storage function of untreated hearts was: AF, 61%; CF, 43%; CO, 55%; work, 48% of control. ET (20 nM) enhanced AF recovery to 85%; CF, 58%; CO, 76%; work, 73% of control (P < 0.05 v untreated). Hoe 140 (D-Arg-[Hyp2, Thi5,8, D-Phe7]BK) (1 nM) a bradykinin receptor antagonist, inhibited ET effect; function returned to the untreated level. Protein kinase C (PKC) inhibitors staurosporine (15 nM) and bisindolylmaleimide I (0.5 microM) also blocked ET effect. After 4 h of cold storage, membrane PKC activity changed little from the prestorage level in the untreated hearts, but was elevated significantly from 52.8 +/- 5.2 pmol/min/mg to 74.7 +/- 8.2 by 20 nM ET (P < 0.05 v untreated). Cytosol PKC did not change during 4 h cold storage with or without ET. Neither end-storage nor end-reperfusion myocardial ATP content was affected by 20 nM ET treatment. In conclusion, ET improves cardiac preservation possibly via bradykinin receptor and PKC without affecting ATP metabolism.

Adenosine Triphosphate↗
PubMed1996

Early enhancement but no late changes of motor responses induced by intracortical microstimulation in the ketamine-anesthetized rat.

The objectives of this study were to determine whether changes in electromyographic (EMG) responses observed during prolonged intracortical microstimulation (ICMS) were due to local plasticity of the motor system or to global changes in the preparation. Local effects would be expressed as changes only along the activated motor pathway, whereas global effects would be expressed as changes also appearing at distant cortical efferent microzones. The results of ICMS in the ketamine-anesthetized rat showed that the size of consecutive EMG responses increased gradually to a relatively stable magnitude over a period of four to six trains of stimuli. This early enhancement of EMG responses was maintained while continuously providing trains of stimuli at 1 Hz. However, it disappeared after a 5-min period of muscle inactivity. This response enhancement in the presence of ketamine (an NMDA, N-methyl-D-aspartate, receptor blocker) suggests that a neuronal mechanism involving non-NMDA-mediated homosynaptic short-term potentiation (STP) was responsible for the early enhancement of EMG responses. To compare ICMS effects at several time intervals it was necessary to average several evoked EMG responses because there was normal biological variability between single EMG responses. To determine the optimal number of EMG responses that would provide a reliable average EMG response, averages of 5, 10, 15, 20, and 25 EMG responses evoked from a single cortical site were collected at 5-min intervals. The results revealed that averages of 10 responses would provide reliable average EMG responses for all subsequent analyses. There were wide fluctuations in the average EMG responses when periodic injections of ketamine were used to maintain a low reflexive state in the animal. Switching to continuous infusion of ketamine abolished these fluctuations but there remained a small drift in the magnitudes of consecutive EMG responses. To test whether this drift reflected local plastic changes in the motor system induced by stimulation or some global changes, EMG responses evoked from another ICMS site were used as control. The rationale was that global effects would affect all motor output sites equally. The sizes of control EMG responses followed a similar time course to those evoked from the test site. Furthermore, standardizing the test EMG responses with respect to the control responses eliminated the drift in response magnitudes. Thus the drift was due to slow global changes in neuronal excitability possibly produced by the anesthesia. In conclusion, late changes occurring after hours of ICMS were not due to plasticity of the motor system but rather to global changes in the preparation, possibly resulting from the inability to set an ideal anesthetic infusion rate that could maintain a constant level of neuronal excitability over long periods of time. However, there was early enhancement of the EMG responses evoked by ICMS due to neuronal plasticity possibly mediated by a non-NMDA mechanism of homosynaptic STP such as post-tetanic potentiation (PTP). This early enhancement would favor recruitment of the previously activated motor pathway and lead to greater consistency in movement execution.

Anesthesia↗
PubMed1996

Pharmacokinetics of the orally administered decongestants pseudoephedrine and phenylpropanolamine in children.

BACKGROUND: There is little published, objective information about pseudoephedrine and phenylpropanolamine in the treatment of children. Our goal was to determine the pharmacokinetics of these medications in young subjects. METHODS: In two sequential double-blind, parallel-group, single-dose studies, 21 children received either pseudoephedrine, 30 or 60 mg, or placebo, and 20 children received either phenylpropanolamine, 20 or 37.5 mg, or placebo. Before dosing and at intervals up to 7 hours after dosing, serum pseudoephedrine or phenylpropanolamine concentrations were measured, and pulse and blood pressure were recorded. In two children receiving each drug, these tests were also performed at 12 and 24 hours, and urine was collected from 0 to 12 and from 12 to 24 hours. RESULTS: In children, the mean (+/-SEM) terminal elimination half-life values for pseudoephedrine, 3.1 +/- 0.5 hours, and for phenylpropanolamine, 2.6 +/- 0.6 hours, were significantly shorter than those found by other investigators in adults. Pharmacokinetics were not dose dependent in the dose ranges studied. CONCLUSION: Further studies of pseudoephedrine and phenylpropanolamine should be performed in children with the use of objective measurements. The widespread use of these medications in young subjects should be reevaluated.

Administration, Oral↗
PubMed1996

Biological treatment of dye wastewaters using an anaerobic-oxic system.

Three dye solutions, namely, C.I. Acid Yellow 17, C.I. Basic Blue 3, and C.I. Basic Red 2, were treated in an upflow anaerobic sludge blanket (UASB) reactor followed by a semi-continuous aerobic activated sludge tank. When hydraulic retention time was about 12 hours, no significant color removal was observed in the aerobic stage. In the anaerobic stage, Acid Yellow 17, Basic Blue 3, and Basic Red 2 were removed by 20%, 72%, and 78%, respectively. To treat wastewater from a dye manufacturing factor with COD concentration of 1200 mg/l and Color of 500 degrees (dilution factor), an UASB reactor (4.5 liters) and an activated sludge tank (5 liters, adjustable), COD and color were removed by more than 83% and 90% at a COD loading rate of 5.3 kg COD/m3-day in the anaerobic stage, and at the hydraulic retention time of 6-10 hours for the anaerobic stage and 6.5 for the aerobic stage. The anaerobic stage of the A/O system removes both color and COD. In addition, it also improves biodegradability of dyes for further aeroic treatment.

Bacteria, Aerobic↗