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Biomedical subjects

X Gu

Publications and source records attributed to X Gu.

At least 217 records · Page 12Linked to original sources
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

Spectrophotometric method for the determination of ascorbic acid with iron (III)-1,10-phenanthroline after preconcentration on an organic solvent-soluble membrane filter.

A solvent-soluble membrane filter is proposed for the simple and rapid preconcentration and spectrophotometric determination of ascorbic acid based on the reduction of 1, 10-phenanthroline (phen)-iron (III), which is collected on a nitrocellulose membrane filter as an ion-associate of the cationic complex of tri,phen-iron (II) [ferroin, Fe(phen)(2+)(3)] with an anionic surfactant (of dodecyl sulfate). The ion-associate collected is dissolved in a small volume of 2-methoxyethanol together with the filter. The colour intensity is measured at 510 nm against the reagent blank and is proportional to the content of ascorbic acid in the range 2.5-50 microg ascorbic acid in 5 ml of solvent with excellent reproducibility (RSD 3.2% for 200 microg 1(-1) ascorbic acid), the enrichment factor achieves 100-fold and detection limits better than 2.0 microg 1(-1) can be obtained. Diverse components of organic and inorganic compounds normally present in fruits, vegetable, beverages and urine do not interfere. The recoveries of the ascorbic acid added to the samples are quantitative.

Journal Article↗
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↗
PubMed1996

Bias-corrected paralinear and LogDet distances and tests of molecular clocks and phylogenies under nonstationary nucleotide frequencies.

The statistical properties of the paralinear and LogDet distances under nonstationary nucleotide frequencies were studied. First, we developed formulas for correcting the estimation biases of the paralinear and LogDet distances, i.e., the bias-corrected distance is estimated by dc = d - 2var(d), where d and var(d) are the estimated distance and sampling variance, respectively. The performances of these formulas and the formulas for sampling variances were examined by computer simulation. Second, we developed a method for estimating the variance-covariance matrix of paralinear distances, so that statistical tests of DNA phylogenies can be conducted in the nonstationary case. Third, a new LogDet-based method for testing the molecular clock hypothesis was developed under nonstationary nucleotide frequencies.

Analysis of Variance↗
PubMed1996

Posttranslational regulation of type I collagen in corneal endothelial cells.

PURPOSE: Type I collagen synthesis in corneal endothelial cells does not correlate with steady state collagen RNA levels; although substantial amounts of alpha 2(I) collagen RNA are present in these cells, type I collagen is not detected. This allowed the authors to investigate the possibility of posttranscriptional control of type I collagen in corneal endothelial cells. METHODS: The alpha 2(I) collagen RNA structures of normal and modulated corneal endothelial cells were analyzed by S1 nuclease protection analysis, whereas the nucleotide sequences were obtained by rapid amplification of cDNA ends technique. In situ hybridization of type I collagen was demonstrated with immunofluorescence; synthesis and degradation of the molecule were analyzed by pulse-chase experiments and then by immunoprecipitation with antiprocollagen I antibody. RESULTS: The cDNA covering the 5'-untranslated region (UTR) of alpha 2(I) collagen RNA obtained from normal corneal endothelial cells and from modulated corneal endothelial cells that predominantly produce type I collagen demonstrate identical sequences in their 5' untranslated and coding sequences. In both mRNA, the length of the 5'-untranslated segment is 127 nucleotides. There were also two AUG codons; the second AUG codon, which is 17 nucleotides upstream from the translation initiation codon, is conserved, as observed in human and chicken alpha 2(I) mRNA. When the sequence covering the 3'-UTR of corneal endothelial alpha 2(I) mRNA was compared with that of alpha 2(I) mRNA obtained from the modulated cells, there were differences in only two nucleotides. The length of the 3'-untranslated segment of each mRNA is 297 nucleotides up to the consensus polyadenylation recognition site (AAUAAAAUAAA), which both cells use. Immunofluorescent staining of corneal tissue in vivo demonstrated that the corneal endothelium stains with anti-type I collagen antibodies, but there is no staining in the underlying Descemet's membrane. In pulse-chase experiments, the newly synthesized type I procollagen, composed of pro alpha 1(I) and pro alpha 2(I) chains as determined by V8 protease peptide mapping, reached the highest intracellular level at 45 minutes, after which its detection decreased. Cells chased for 120 minutes demonstrated no trace of type I procollagen in the cell layer; medium fractions showed no detectable type I procollagen during the entire 120-minute chase. CONCLUSIONS: These results suggest that type I collagen is synthesized in corneal endothelial cells and that such undesired expression is regulated at the posttranslational level, perhaps by intracellular degradation.

Amino Acid Sequence↗
PubMed1996

Fibroblast growth factor 2 uses distinct signaling pathways for cell proliferation and cell shape changes in corneal endothelial cells.

PURPOSE: Fibroblast growth factor 2 (FGF-2) is not only a potent mitogen, it is a modulator for corneal endothelial cells. To define how the modulation activities of FGF-2 are mediated, we used pharmacologic inhibitors to examine the association of phospholipase C-gamma 1 (PLC-gamma) with FGF receptor or with cytoskeleton. METHODS: Cell proliferation was determined either by the incorporation of 3H-thymidine into DNA or by counting cell numbers in the absence or presence of the inhibitors. The protein expression was analyzed by immunoprecipitation and immunoblot analysis. Cell shape change was determined by phase-contrast microscopy. RESULTS: FGF-2 stimulated DNA synthesis, whereas genistein inhibited the FGF-2-mediated cell proliferation in a dose-dependent manner, regardless of the concentration of FGF-2. The PLC-gamma 1 specific antisense oligonucleotide primer was able to inhibit cell proliferation by 25% in the absence of FGF-2; however, the antisense primer was not able to override the action of FGF-2. Fibroblast growth factor receptor was phosphorylated on treatment of the cells with FGF-2; however, 24-hour treatment with the growth factor significantly reduced phosphorylation of the receptor. Phospholipase C gamma 1 appears to be abundant in cytoplasm in the absence and presence of FGF-2, and a minor portion of the molecule is translocated to membrane after treatment with FGF-2; genistein inhibited the translocation. When the cytoskeleton fraction of the normal and the modulated corneal endothelial cells was immunoprecipitated with PLC-gamma 1 antibodies, PLC-gamma 1, actin, and vinculin were coprecipitated in both cell cultures. Phospholipase C gamma 1 associated with cytoskeleton was phosphorylated on treatment of the cells with FGF-2. In the presence of FGF-2 of the modulated cells, cytochalasin B, which did not revert the modulated cell morphology, abolished the association of PLC-gamma 1 with actin and vinculin; colchicine, which did revert the modulated cell shape to the polygonal shape, did not block the association of these three molecules. Interestingly, colchicine slightly enhanced the stimulatory effect of FGF-2 on corneal endothelial proliferation in contrast to the effect of cytochalasin B, which slightly decreased the FGF-2 action on cell proliferation. CONCLUSIONS: The association of PLC-gamma 1 with cytoskeleton plays a role in cell proliferation, whereas the association of PLC-gamma 1 with actin and vinculin has no effect on cell shape changes. These findings indicate that FGF-2 appears to use distinct signaling pathways for cell proliferation and cell shape changes in corneal endothelial cells.

Animals↗
PubMed1996

[Radiation therapy of esophageal carcinoma: a report on 180 cases].

One hundred eighty patients with pathologically proved esophageal carcinoma accepted for surgery, for various resons, were given radical radiation therapy. The length of the lesions ranged from 2 to 9 cm. They were treated either by the isocenter technique alone or A-P plus isocenter irradiation to a total dose of 50-70 Gy/5-7 wk. The 1-, 3- and 5-year survival rate was 64.4%, 34.4% and 23.3%, respectively. The 3- and 5-year survival rates showed that lesions in the upper third responded to radiotherapy better than did those in the middle and lower thirds (P < 0.05). The 5-year survival of patients with upper third lesions treated with radiation alone (44.5%) was slightly better than that of surgery. The result of lesions in the middle third was slightly inferior, and that of lower third was even more inferior to that of surgery. The result of radiation alone for operable esophageal carcinoma was comparable to that of surgery.

Adult↗
PubMed1995

Distinct aspects of neuronal differentiation encoded by frequency of spontaneous Ca2+ transients.

Stimulation of transient increases in intracellular calcium (Cai2+) activates protein kinases, regulates transcription and influences motility and morphology. Developing neurons generate spontaneous Cai2+ transients, but their role in directing neuronal differentiation and the way in which they encode information are unknown. Here we image Ca2+ in spinal neurons throughout an extended period of early development, and find that two types of spontaneous events, spikes and waves, are expressed at distinct frequencies. Neuronal differentiation is altered when they are eliminated by preventing Ca2+ influx. Reimposing different frequency patterns of Ca2+ elevation demonstrates that natural spike activity is sufficient to promote normal neurotransmitter expression and channel maturation, whereas wave activity is sufficient to regulate neurite extension. Suppression of spontaneous Ca2+ elevations by BAPTA loaded intracellularly indicates that they are also necessary for differentiation. Ca2+ transients appear to encode information in their frequency, like action potentials, although they are 10(4) times longer in duration and less frequent, and implement an intrinsic development programme.

Action Potentials↗
PubMed1995

Spontaneous calcium transients regulate neuronal plasticity in developing neurons.

Calcium ions play critical roles in neuronal differentiation. We have recorded transient, repeated elevations of calcium in embryonic Xenopus spinal neurons over periods of 1 h in vitro and in vivo, confocally imaging fluo 3-loaded cells at 5 s intervals. Calcium spikes and calcium waves are found both in neurons in culture and in the intact spinal cord. Spikes rise rapidly to approximately 400% of baseline fluorescence and have a double exponential decay, whereas waves rise slowly to approximately 200% of baseline fluorescence and decay slowly as well. Imaging of fura 2-loaded neurons indicates that intracellular calcium increases from 50 to 500 nM during spikes. Both spikes and waves are abolished by removal of extracellular calcium. Developmentally, the incidence and frequency of spikes decrease, whereas the incidence and frequency of waves are constant. Spikes are generated by spontaneous calcium-dependent action potentials and also utilize intracellular calcium stores. Waves are produced by a mechanism that does not involve classic voltage-dependent calcium channels. Spikes are required for expression of the transmitter GABA and for potassium channel modulation. Waves in growth cones are likely to regulate neurite extension. The results demonstrate the roles of a novel signaling system in regulating neuronal plasticity, that operates on a time scale 10(4) times slower than that of action potentials.

Animals↗
PubMed1995

The size distribution of insertions and deletions in human and rodent pseudogenes suggests the logarithmic gap penalty for sequence alignment.

The size distributions of deletions, insertions, and indels (i.e., insertions or deletions) were studied, using 78 human processed pseudogenes and other published data sets. The following results were obtained: (1) Deletions occur more frequently than do insertions in sequence evolution; none of the pseudogenes studied shows significantly more insertions than deletions. (2) Empirically, the size distributions of deletions, insertions, and indels can be described well by a power law, i.e., fk = Ck-b, where fk is the frequency of deletion, insertion, or indel with gap length k, b is the power parameter, and C is the normalization factor. (3) The estimates of b for deletions and insertions from the same data set are approximately equal to each other, indicating that the size distributions for deletions and insertions are approximately identical. (4) The variation in the estimates of b among various data sets is small, indicating that the effect of local structure exists but only plays a secondary role in the size distribution of deletions and insertions. (5) The linear gap penalty, which is most commonly used in sequence alignment, is not supported by our analysis; rather, the power law for the size distribution of indels suggests that an appropriate gap penalty is wk = a + b ln k, where a is the gap creation cost and blnk is the gap extension cost. (6) The higher frequency of deletion over insertion suggests that the gap creation cost of insertion (ai) should be larger than that of deletion (ad); that is, ai - ad = ln R, where R is the frequency ratio of deletions to insertions.

Animals↗
PubMed1995

Proton nuclear magnetic resonance studies on huwentoxin-I from the venom of the spider Selenocosmia huwena: 1. Sequence-specific 1H-NMR assignments.

The complete sequence-specific assignments of resonances in the 1H-NMR spectrum of huwentoxin-I from the Chinese bird spider, Selencocosmia huwena, is described. A combination of two-dimensional NMR experiments including 2D-COSY, 2D-NOESY, and 2D-TOCSY has been employed on samples of the toxin dissolved in D2O and in H2O for assignment purposes. Protons belonging to spin systems for each of the 33 amino acids were identified. The sequence-specific assignments were facilitated by the identification of d alpha N connectivities on the fingerprint regions of the COSY and NOESY spectra and were supported by the identification of dNN and d alpha N connectivities in the TOCSY and NOESY spectra. These studies provide a basis for the determination of the solution-phase conformation of this toxin.

Amino Acid Sequence↗