Biomedical subjects

K Xu

Publications and source records attributed to K Xu.

At least 217 records · Page 12Linked to original sources

PubMed1994

[Quantitative study on DNA-adduct in normal lung tissues of smoking and non-smoking lung cancer patients].

Lung tissues from 32 cases of lung cancer with surgical operation, 22 smokers and 10 nonsmokers, were analyzed with P1-mediated modification of 32P-postlabelling technique. The level of lung DNA-adduct in cigarette smokers was higher that in nonsmokers with significant difference (P < 0.001). Autoradiogram showed a diagonal radioactive zone in smokers' lung tissues. Correlation analysis indicated DNA-adduct in lung tissues increased with the number of cigarettes smoked with a regression equation of Y = 0.411 X + 3.52, r = 0.74, P < 0.001.

Adult↗

PubMed1994

Molecular characteristics of four new depressant insect neurotoxins purified from venom of Buthus martensi Karsch by HPLC.

Suitable pattern and high yield were obtained when the reverse-phase performance liquid chromatography (RP-HPLC) was used to separate neurotoxins from venom of Chinese scorpion Buthus martensi Karsch. Using this technique, the venom was first separated to two main regions. The toxicity tests show that the insect-selective neurotoxical components are concentrated in the latter region, from which five insect-selective neurotoxins designated by BmK IT1-IT5 were obtained. According to the results of the toxicity test as well as the amino acid composition and N-terminal analyses, BmK IT1 is the excitatory insect neurotoxin as reported in a previous paper, and the others are the newly found depressant insect-selective neurotoxins. The molecules of all the four toxins are single-chain minipeptides of about 60 amino acids. Their isoelectric points (pI) are between 8.3 and 8.5. The fact that BmK IT2 loses completely its insect toxicity after being modified by fluorochrome shows that the positive charges on the molecular surface of this kind of toxins are important to maintaining the bioactivity of the molecules.

Amino Acid Sequence↗

PubMed1994

Amino acid sequence of an excitatory insect-selective toxin (BmK IT) from venom of the scorpion Buthus martensi Karsch.

The insect-selective neurotoxin (BmK IT) of scorpion Buthus martensi Karsch was first reduced and S-alkylated, and then digested by TPCK-trypsin and Staphylococcus aureus V-8 Protease. The enzymatic peptides were purified on TLC-plastic sheet and submitted to determine their amino acid compositions and sequences. The sequence of the 70 amino acid residues of BmK IT was established with reference to the primary structure of AaH IT, another excitatory insect-selective toxin from the venom of North African scorpion Androctonus australis Hector. About 75% of the homologous sequence was found in the molecules of BmK IT and AaH IT. It is obvious that the results contribute toward better understanding of the molecular structure characteristics, structure/activity relationship of scorpion insect-selective toxins, and they can serve as the molecular basis for utilizing the toxins as a tool to clarify molecular mechanism involved in channel gating, and to infer the possibility of developing them as new selective bioinsecticides.

Amino Acid Sequence↗

PubMed1993

On two transposable elements from Bacillus stearothermophilus.

Two transposable elements, IS5376 and IS5377, were identified in the thermophile Bacillus stearothermophilus CU21 based upon the following criteria: (1) both were found to appear on different plasmids introduced into the same host CU21; (2) signals of homology were found between the genomic DNA of CU21 and each of them; (3) different numbers of Southern hybridization bands were found for the genomic DNA of different strains of B. stearothermophilus; and (4) characteristic inverted repeats at both ends and direct repeats of the target DNA adjacent to them were found for both IS5376 and IS5377. Two open reading frames (ORFs) were detected for IS5376 and one for IS5377. The putative coding products of the ORFs are homologous to those of known ISs from mesophiles and are considered to be transposases. The results of analyses of nucleotide sequence and the deduced amino acid sequence suggest that IS5376 is a member of the IS21 family and that IS5377 is a member of the IS4 family.

Amino Acid Sequence↗

PubMed1993

Primer extension preamplification for detection of multiple genetic loci from single human blastomeres.

A new technology called primer extension preamplification (PEP), which has been applied to single spermatozoa, increases the amount of polymerase chain reaction (PCR) templates by amplifying DNA of the whole genome. The current investigation was aimed at applying PEP to single human blastomeres. Two blastomeres with nuclei from arrested embryos were selected for this study. Using three different PEP protocols (experiments I, II and III), DNA from single blastomeres was amplified using 15-base oligonucleotide random primers. The efficiency of the procedure was determined by further amplifications of aliquots of the PEP products with two specific sequences. Three aliquots from each PEP product were used as PCR templates for the human X chromosome (X) or the exon 10 of the cystic fibrosis gene (CF). PCR amplified products were analysed by gel electrophoresis. In experiment I, when X primers were used, positive signals were detected in all 10 embryos (100%), 90.0% (18/20) of the blastomeres, and in 80.0% (96/120) of the replicates. When CF primers were amplified, all embryos (100%, 10/10), 90.9% (18/20) of the blastomeres and 78.3% (47/60) of the replicates were positive. In experiment II, efficiency was significantly reduced when total time for the procedure was minimized from 8 h to 5 h and 45 min. Although the time was further reduced to 4 h and 40 min in experiment III, the efficiency remained the same as in experiment I when the volume of PEP was reduced from 60 microliters (experiments I and II) to 40 microliters. One out of 132 control replicates (0.8%) was contaminated.(ABSTRACT TRUNCATED AT 250 WORDS)

Blastomeres↗

PubMed1993

An oxygen-dependent coproporphyrinogen oxidase encoded by the hemF gene of Salmonella typhimurium.

The 8th step in the 10-step heme biosynthetic pathway of Salmonella typhimurium is the oxidation of coproporphyrinogen III to protoporphyrinogen IX. On the basis of genetic studies, we have suggested that this reaction may be catalyzed by either of two different enzymes, an oxygen-dependent one encoded by hemF or an oxygen-independent enzyme encoded by hemN. Here, we report the cloning of the S. typhimurium hemF gene and its DNA sequence. The predicted amino acid sequence of the HemF protein is 44% identical to that of the coproporphyrinogen oxidase encoded by the yeast HEM13 gene. The wild-type S. typhimurium strain LT-2 produces an oxygen-dependent coproporphyrinogen oxidase activity detectable in crude extracts, which is not found in hemF mutants and is overproduced in strains carrying the hemF gene on a multicopy plasmid. the hemF gene is the second gene in an operon with an upstream gene with an unknown function, whose amino acid sequence suggests a relation to amidases involved in cell wall synthesis or remodeling. The upstream gene and hemF are cotranscribed from a promoter which was mapped by primer extension. A weaker, hemF-specific promoter is inferred from the behavior of an omega-Cm insertion mutation in the upstream gene. Although this insertion decreases expression of beta-galactosidase about 7.5-fold when placed upstream of a hemF-lacZ operon fusion, it still allows sufficient HemF expression from an otherwise wild-type construct to confer a Hem+ phenotype. The hemF operon is transcribed clockwise with respect to the genetic map.

Amino Acid Sequence↗

PubMed1993

Extracellular catecholamine levels in rat hippocampus after a selective alpha-2 adrenoceptor antagonist or a selective dopamine uptake inhibitor: evidence for dopamine release from local dopaminergic nerve terminals.

The effect of 6-chloro-2,3,4,5-tetrahydro-3-methyl-1-H-3-benzazepine (SKF 86466), a selective nonimidazoline alpha-2 adrenoceptor antagonist, on hippocampal release of norepinephrine and dopamine in conscious rats was investigated by in vivo microdialysis and high-pressure liquid chromatography. Additionally, extracellular concentrations of hippocampal dopamine (DA) and norepinephrine (NE), during infusion of selective monoamine uptake inhibitors, were determined in freely moving rats. The basal concentration of NE in the dialysate was 4.9 +/- 0.3 pg/20 microliters. Intravenous administration of 5 or 10 mg/kg of SKF 86466 was associated with a transient increase (30 min) of 2-fold (12 +/- 1 pg/20 microliters; P < .05) and 8-fold (39 +/- 3 pg/20 microliters; P < .05), respectively, in dialysate NE, whereas a 1-mg/kg dose had no effect. DA was not detected in basal dialysates, but after the administration of 5 or 10 mg/kg of SKF 86466, 3.9 +/- 0.4 and 6.4 +/- 0.6 pg/20 microliters, respectively, was present in the dialysates. The maximum increase in dialysate DA was reached 60 to 90 min after SKF 86466. The DA was not derived from plasma because plasma NE was elevated after the 5 mg/kg dose of SKF 86466 whereas no plasma DA was detected. In order to determine whether DA was present in noradrenergic nerve terminals, the dopamine beta-hydroxylase inhibitor SKF 102698 was administered (50 mg/kg i.p.). The inhibitor decreased dialysate NE but DA was still not detected in the dialysate.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗

PubMed1993

[The genotyping of HLA-D region and specific RFLP patterns for Chinese Han population].

The HLA class II antigens play very an important role in presenting foreign antigens. The class II gene typing at the DNA level possesses higher capability to recognize polymorphism so that it can disclose new specificities. According to the RFLP patterns of DRB and DQA genes for Caucasian HTC and some Chinese homozygous cells, we typed 90 randomly sampled healthy Chinese Hans in Shanghai area, and compared the results obtained with those from serological typing. In addition to being reliable and superior to serological typing, we found some unique RFLP patterns of the HLA-D region in Chinese Han population based on comparison with Caucasian patterns.

Blood Grouping and Crossmatching↗

PubMed1993

Saltatory conduction and a novel type of excitable fenestra in shrimp myelinated nerve fibers.

The findings of saltatory conduction in the invertebrate giant nerve fibers were mentioned, and the experiments for analyzing the mechanism of impulse conduction in the giant myelinated nerve fibers of Penaeus orientalis and Penaeus japonicus were reviewed. Saltatory conduction was also found in many middle- and small-sized myelinated nerve fibers of, at least, 6 species of Penaeus shrimps. Saltatory conduction with its morphological basis in myelinated nerve fibers of vertebrates and invertebrates were compared, and it was concluded that the myelination of the nerve fibers in vertebrates and invertebrates has occurred independently.

Animals↗

PubMed1993

[Grafting of autogenous jugular vein and glutaraldehyde-stabilized human umbilical vein in dogs].

The glutaraldehyde-stabilized human umbilical cord vein (HUV) was implanted to the intrarenal aorta in dogs, by using autogenous jugular vein (AJV) as control. The healing mechanism was shown by angiography, radioisotope scanning Doppler ultrasound, LM, SEM and TEM. The patency rate in 6 months was 95.2% in AJV and 87.5% in HUV. No significant difference was noted between the two veins (P > 0.05). Pathohistological study of AJV and HUV after implantation showed that there were three stages: acute injury, acute inflammatory reaction and hyperplastic repairing of tissues. The new endothelial cells of AJV grew earlier and faster than those of HUV. But, both veins were endothelialized 6 months after operation. The subendothelium of new intima consisted of fibroblasts and collagen fibres less myointimal cells derived from smooth muscle cells in the media. The media and the adventilized were replaced by fibrous connective tissue. HUV stabilized with 0.5% glutaraldehyde for grafting caused no immunologic rejection, and had the structure of the venous wall and antithrombotic function, keeping the grafts patent.

Animals↗

PubMed1993

[Nilestriol prevents osteoporosis in ovariectomized rats].

In order to determine the effects and mechanism of Nilestriol upon bone metabolism, 4-month aged female SD rats were divided randomly into three groups: The OVX group subjected to bilateral ovariectomy, the SHAM group to sham operation, the Nilestriol (CEE3) group to bilateral ovariectomy and treated with CEE3 0.15 mg/100 g BW once a week for 10 weeks. The CEE3 was introduced directly into the stomach from the first day after operation. All rats were killed 10 weeks after operation and their right proximal tibiae were processed undercalcified for quantitative bone histomorphometry. The weights of bone and inorganic matter (ash content) and content of calcium, phosphorus of right humeral were measured. The results showed that in the OVX group the trabecular bone volume, the trabecular thickness, the content of calcium bone, and the ratios of bone weight and ash weight to body weight were all significantly reduced. The bone loss was associated with an increase in bone remodeling; the bone resorption appeared much more marked than the bone formation. In contrast, the ovariectomized animals treated with CEE3 had normalization of bone mass and a declined index of bone resorption and formation which recovered the balance of bone remodeling. It suggested that CEE3 is successful in prevention of bone loss in OVX rats. It is convinced of using Nilestriol to prevent postmenopausal osteoporosis.

Animals↗

PubMed1993

Serologic responses to nerve antigens in sooty mangabey monkeys with experimental leprosy.

Eight sooty mangabey monkeys were inoculated intravenously and intradermally with varying doses of Mycobacterium leprae from 4.8 x 10(7) to 4.8 x 10(10). Serum samples were obtained from the animals at intervals of about 3 months for 90 months, and were examined for IgM and IgG antibodies to nerve antigens, including ceramide, galactocerebroside (GC), and asialo-GM1 (AGM1), using an enzyme-linked immunosorbent assay (ELISA). The serological results were then compared with clinical findings, particularly nerve involvement. Of 8 mangabey monkeys inoculated with M. leprae, 7 animals had clinical leprosy; 6 of them had nerve damage, including neurologic deformities in 4 monkeys and nerve enlargement in 2. Median time for the initial signs of leprosy was 10 months postinoculation (p.i.), a range from 4 to 35 months. In contrast, nerve damage was noted rather late, about 35 to 86 months p.i. (median 54 months). The major immunoglobulin class to ceramide, GC, and AGM1 antigens was IgM, and the antibody responses to the nerve antigens appeared from 15 to 63 months p.i. (median 37 months). Antineural antibodies were thus detectable about 18 months (range -2 to 60 months) prior to observable nerve damage. In addition, elevation of antineural antibody levels were predictive of clinical exacerbation of the disease and neuritic damage. This study suggests that antineural antibodies are produced during the course of M. leprae infection and may be indicative of nerve damage, such as neurological deformities or nerve enlargement, in leprosy patients.

Animals↗

PubMed1992

[Transjugular intrahepatic portosystemic stent shunt (TIPSS) with use of Rösch-Uchida transjugular liver access set--evaluation by CT and its clinical application].

Appropriateness of the Rösch-Uchida transjugular liver access set designed for TIPSS procedure was confirmed, especially about the catheter angle and effective length of the 20 G puncture needle, by CT analysis on three dimensional vascular anatomy of the liver. Clinically, TIPSS using the set was successfully made for two patients, connecting superior right hepatic vein with right portal vein in one patient and middle hepatic vein with left portal vein in another patient with hypoplastic right portal vein. Prior to TIPSS procedure, verification of vascular anatomy on CT images is the key to success of TIPSS in safe.

Evaluation Studies as Topic↗

PubMed1992

Leukotriene C4 uses a probenecid-sensitive export carrier that does not recognize leukotriene B4.

The export of leukotriene (LT) C4 from human eosinophils, a carrier-mediated process that is temperature-dependent and saturable, was characterized further in eosinophils and in two human leukemia cell lines that do not present an intact 5-lipoxygenase pathway. In eosinophils, KG-1 cells, and dimethyl sulfoxide (DMSO)-differentiated HL-60 cells, the respective Q10 values for temperature-dependent LTC4 export were 3.7, 3.3, and 3.4 and for energy of activation were 28.2 kcal/mol, 23.0 kcal/mol, and 27.8 kcal/mol (1 kcal = 4.18 kJ). When human eosinophils, KG-1 cells, and DMSO-differentiated HL-60 cells were preloaded with defined amounts of intracellular LTC4 by incubation with LTA4 and with incremental amounts of a glutathione conjugate, S-dinitrophenyl glutathione (GS-DNP) by sequential incubation with 1-chloro-2,4-dinitrobenzene, GS-DNP inhibited the export of LTC4 in a dose-dependent manner. By plotting the ratio of total GS-DNP (cell retained plus released) to the sum of total GS-DNP plus total LTC4 against the percentage inhibition of LTC4 release, IC40 values of 0.839, 0.803, and 0.841 were obtained for eosinophils, KG-1 cells, and DMSO-differentiated HL-60 cells, respectively. When cells preloaded with LTC4 were resuspended in incremental concentrations of the organic acid transport inhibitor, probenecid, there was a dose-dependent decrease in LTC4 release; GS-DNP and probenecid inhibited LTC4 release in a cumulative fashion, whereas neither inhibited the release of LTB4 from preloaded nondifferentiated HL-60 cells. Therefore, LTC4 export from cells of bone marrow origin occurs through a probenecid-sensitive membrane carrier shared by other glutathione conjugates and distinct from the LTB4 carrier export system.

Carrier Proteins↗

PubMed1992

The genes required for heme synthesis in Salmonella typhimurium include those encoding alternative functions for aerobic and anaerobic coproporphyrinogen oxidation.

Insertion mutagenesis has been used to isolate Salmonella typhimurium strains that are blocked in the conversion of 5-aminolevulinic acid (ALA) to heme. These mutants define the steps of the heme biosynthetic pathway after ALA. Insertions were recovered at five unlinked loci: hemB, hemCD, and hemE, which have been mapped previously in S. typhimurium, and hemG and hemH, which have been described only for Escherichia coli. No other simple hem mutants were found. However, double mutants are described that are auxotrophic for heme during aerobic growth and fail to convert coproporphyrinogen III to protoporphyrinogen IX. These mutant strains are defective in two genes, hemN and hemF. Single mutants defective only in hemN require heme for anaerobic growth on glycerol plus nitrate but not for aerobic growth on glycerol. Mutants defective only in hemF have no apparent growth defect. We suggest that these two genes encode alternative forms of coproporphyrinogen oxidase. Anaerobic heme synthesis requires hemN function, while either hemN or hemF is sufficient for aerobic heme synthesis. These phenotypes are consistent with the requirement of a well-characterized class of coproporphyrinogen oxidase for molecular oxygen.

Aerobiosis↗

PubMed1992

Resistance of the snake neuromuscular junction to the blocking effect of beta-bungarotoxin.

beta-Bungarotoxin at a concentration of 0.05 microM was enough to block successively the nerve-evoked intracellular action potential of muscle fiber, the end-plate potential, and miniature end-plate potentials within 60, 90, and about 180 min, respectively, in the isolated nerve-muscle preparation of the frog. On the other hand, at the snake neuromuscular junction beta-bungarotoxin caused an initial transient reduction and a following sustained facilitation of the miniature end-plate potential discharge, but did not block the nerve-evoked intracellular action potential of muscle fiber at a concentration of as high as 50 microM over 4 h. The results show that beta-bungarotoxin binds to snake motor nerve ending without leading to the transmission block, probably due to lacking the target of action.

Action Potentials↗

PubMed1992

[Channel-forming activity at planar lipid bilayer of the membrane active polypeptide B form venom of Bungarus fasciatus].

Using planar lipid bilayer formed by lecithin and cholesterol (20 and 5 mg/ml respectively in N-decane) the channel-forming activity of the membrane active polypeptide B(BMAP B) from the venom of Bungarus fasciatus was investigated. Under the existence of a voltage or a salt concentration gradient between two sides of the bilayer, unit conductance fluctuation and a decrease in steady state resistance accompanying BMAP B incorporation and channel formation were observed. By measuring the reversal potential in an asymmetric solution, the selectivity of the BMAP B-channel was estimated having a value of PK/PC1 = 1.4. Divalent cations, such as Ba2+, Ca2+ inhibited the channel activity as they did in biomembranes. These data might provide an explanation for the depolarizing effect of the membrane active polypeptide on the native membranes.

Animals↗

PubMed1992

[Effects of beta-agkistrodotoxin on synaptic transmission in toad sympathetic ganglia].

The effects of beta-agkistrodotoxin (beta-AgTX) on synaptic transmission of the toad sympathetic ganglia were investigated by intracellular recording techniques. Superfusion of beta-AgTX (30 microgram/ml, 5-15 min) reversibly inhibited the cholinergic fast excitatory postsynaptic potential (f-EPSP, n = 16) and the fast components of acetylcholine (ACh) potential induced by micropressure administration of ACh (n = 24). Comparison of beta-AgTX effect in the same cell group showed significantly different inhibition rates on f-EPSP (77.2 +/- 27.7%) and ACh potential (25.5 +/- 17.5%) (n = 6, P less than 0.01, F test). During application of beta-AgTX (30 or 50 micrograms/ml) for 15-30 min, no detectable change was found in non-cholinergic late slow EPSPs (n = 22). The results suggest that beta-AgTX selectively inhibits the cholinergic transmission of the toad sympathetic ganglia by both presynaptic and postsynaptic mechanism.

Animals↗