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Biomedical subjects

Q Liu

Publications and source records attributed to Q Liu.

At least 703 records · Page 39Linked to original sources
PubMed1992

The effect of methylation outside the recognition sequence of restriction endonuclease PvuII on its cleavage efficiency.

This study is to extend our earlier observation that Dam and Dcm methylation outside the PvuII recognition sequence inhibited PvuII cleavage in one of the three PvuII sites of pGEM4Z-ras DNA. In this paper, a new recombinant plasmid DNA, pGEM4-SV40ori-anti-ras, was constructed which has only two PvuII sites, I and II. The Dam and Dcm-methylated and unmethylated DNAs were produced in Escherichia coli and linearized by ScaI. The DNA molecules were digested with different amounts of PvuII. The results show that by comparing the DNA fragment number and intensity of the partial and final products in agarose gel, PvuII site I on the methylated DNA molecule was digested four- to eight-fold more slowly than site II. In the unmethylated plasmid DNA, the two PvuII sites were cleaved at about the same rate. The difference was caused only by methylation of Dam and Dcm sites outside the PvuII recognition sequence. A methylated Dam site immediately adjacent to the less efficiently cut PvuII site I may be responsible for the inhibitory effect. We suggest that a new parameter, involving methylation of sites outside the recognition sequence, be considered in kinetic experiments on cleavage.

Base Sequence↗
PubMed1992

Analysis of the temporal and spatial dependence of the eddy current fields in a 40-cm bore magnet.

Eddy current fields, generated in an animal-size superconducting NMR magnet by a nominally rectangular pulsed transverse gradient applied in the vertical direction, have been studied by measuring the offset frequency of the proton NMR signal obtained from a small spherical sample. Measurements were made, after various time delays, at nine different locations in the sample space. Analysis of the data shows that the time-dependent fields at all nine locations are quite well accounted for by the superposition of only four independent exponentially decaying components that have time constants in the range from 9 to 400 ms. Two of these were found to be caused by eddy currents generated in the magnet structure. They generate primarily linear gradients, though one of them also produces a B0 shift, indicating a significant asymmetry about the isocenter of the conducting structure in which the eddy current flows. The other two exponentially decaying components, which had very different time constants from the eddy currents and also initial amplitudes of the opposite sign, were generated by the preemphasis unit. This calls into question the procedure used to adjust the preemphasis unit and an alternative method is proposed.

Artifacts↗
PubMed1992

Mapping of the mouse Rxr loci encoding nuclear retinoid X receptors RXR alpha, RXR beta, and RXR gamma.

Recently, a novel subgroup of nuclear hormone receptors called RXRs implicated for retinoid-mediated gene regulation have been identified. RXRs appear to interact with many other nuclear hormone receptors and modulate their functions. We have mapped genetic loci Rxra, Rxrb, and Rxrg encoding three RXR subtypes, RXR alpha, RXR beta, and RXR gamma, respectively, using interspecific backcross mice. None of the Rxr loci cosegregated with each other or with the retinoic acid receptor loci (Rar) mapped previously. Rxra mapped to Chr 2 near the centromere, Rxrb mapped to the H-2 region of Chr 17, and Rxrg was tightly linked to the Pbx gene on distal Chr 1. These results underscore that RXR genes are dispersed in the genome.

Animals↗
PubMed1992

Epidemiology of Helicobacter pylori in southern China: identification of early childhood as the critical period for acquisition.

A large cross-sectional study to investigate the prevalence and possible modes of transmission of Helicobacter pylori was done in southern China. Serum samples (1727) were collected from Guangzhou city and three rural areas of Guangdong Province, and the prevalence of H. pylori infection was determined using an ELISA. Each subject completed a questionnaire. The overall prevalence of H. pylori infection was 44.2%; a significantly higher prevalence was found in Guangzhou (52.4%) than in the rural areas (38.6%). This difference was generally reflected in the group 0-5 years old, but the rate of increase in seroprevalence for H. pylori over 5 years of age was similar (1%/year). This study provides important new data on the acquisition of H. pylori, particularly in the early years of life, and shows that density of living conditions is a prime determinant in the acquisition of H. pylori.

Adolescent↗
PubMed1992

Large glomerular size in Pima Indians: lack of change with diabetic nephropathy.

The mean glomerular volume, glomerular fraction of cortical volume, and percentage of obsolescent glomeruli were calculated in kidney specimens from autopsies on 34 Pima Indians, of whom 15 had non-insulin dependent diabetes mellitus and kidney disease of diabetes mellitus. These values were compared with those of black, white, and non-Pima native American individuals without diabetes mellitus. Glomerular volume in the Pima Indians was similar in the diabetic and nondiabetic subjects and significantly greater than in the white subjects. Black and non-Pima native American individuals had glomerular volumes intermediate between white individuals and Pima Indians. The mean glomerular volume was not affected by the number of obsolescent glomeruli in diabetic Pima Indians. The glomerular volume fraction was greater in the Pimas than in the other groups. These data showed that glomerular volume in the Pima Indians was significantly greater than that in white subjects. There was no difference between diabetic and nondiabetics Pimas, and glomerular size was not correlated with the presence or degree of glomerulosclerosis in this population.

Adolescent↗
PubMed1992

Molecular analysis of the Neurospora clock: cloning and characterization of the frequency and period-4 genes.

Genetic analysis of Neurospora crassa has identified many mutants that affect the biological clock. In this article we review the cloning of two of these genes, frq and prd-4. Both genes were isolated using a chromosome walk technique. Subcloning experiments and subsequent Northern analysis of frq implicate the importance of two transcripts that emanate from this locus. In preliminary data, no protein-coding region is evident in the smaller transcript; the larger transcript contains a 962-amino acid open reading frame. The open reading frame shows limited homology to per, a clock gene identified in Drosophila. Sequence analysis of all existing frq alleles suggests that the defect in each case lies within the open reading frame. Successful cloning of the prd-4 gene required walking a distance of greater than 40 kb. A physical map of this region has been constructed using restriction analysis. The dominance-recessive relationship of prd-4 and prd-4+ was established by examining the period lengths of strains harboring a wide range of prd-4/prd-4+ nuclear ratios.

Amino Acid Sequence↗
PubMed1992

DA1 receptor mediated regulation of Na(+)-H+ antiport activity in rat renal cortical brush border membrane vesicles.

Our previous studies indicate that dopamine (DA) plays an important role in regulating renal sodium (Na+) metabolism during high Na+ intake, and that DA1 receptors are involved in natriuretic response to acute volume expansion. It has also been shown that in addition to the changes in renal hemodynamics, the natriuretic response produced by exogenously administered DA and DA1 receptor agonists appears to be due to alterations in renal tubular sodium transport mechanisms. This study was designed to investigate the DA1 receptor-mediated changes in Na(+)-H+ antiport activity in tubular brush border membranes of rat kidney. The Na(+)-H+ antiport activity, measured as the amiloride-sensitive Na+ influx in BBMV, was inhibited by 37%, 46%, 33%, and 42% by 1 microM DA, SKF 82958, SKF 38393, and fenoldopam respectively. The DA1 antagonist SCH 23390 increased the antiport activity when given alone, while when administered with an agonist it attenuated the effects of the agonist on the antiporter. DA2 agonists and antagonists failed to affect the antiport activity. These results indicate that the inhibitory effects of DA and DA receptor agonists on Na(+)-H+ antiport activity in renal cortical BBMV were mediated by the DA1 receptors.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1992

[Studies on the analysis of stereoisomer of agarofurans by GC and GC-MS].

The method for separation and identification of three pairs of agarofuran epimers (alpha-and beta-dihydroagarofuran, alpha- and beta-baimuxinol, alpha- and beta-baimuxinol methyl ether) by HRGC and HRGC/MSD is described. The proportion of each pair of isomers was determined and the analytical procedure for isomers of sesquiterpenes was established. Thus, the correct synthetic route can be effectively guided and the study of agarofuran synthesis can be greatly accelerated. The method provides a reliable basis for identifying the products. MS data given in Table 2 may be useful for the identification of agarofuran derivatives.

Chromatography, Gas↗
PubMed1992

[Relation between the occurrence of malignant arrhythmia during acute myocardial ischemia and the weight of ischemic myocardium in goats].

The coronary collateral circulation of goat is very spare, so myocardiac ischemia model of goat can simulate the patient previously with normal coronary circulation and suddenly developing complete occlusion of coronary arteries. In this study 80 Chengdu goats were used, and the branches of their left coronary artery were ligated. Ventricular tachycardia (VT) developed in 23 goats and ventricular fibrillation (VF) in 39 goats. VT and VF both occurred in the early phase of acute myocardial ischemia, and both had 6 min as the median time of onset. In 71 cases data on the weight of myocardiac ischemic area were collected, in which the weight percentage of ischemic area relating to the ventricles of 34 goats with VF was significantly higher than that of 37 goats without VF (35.4 +/- 2.4% vs 19.5 +/- 1.9%). After coronary ligation, 9 cases directly precipitated into VF which could not be defibrillated. In the remaining 62 cases, the weight percentage of ischemic area of 21 cases with VT was higher than that of 41 cases without VT (32.9 +/- 2.8% vs 20.9 +/- 2.1%). The relationships between the incidence of VT or VF and the weight percentage of ischemic area were fitted with logistic curve. The likelihood of occurrence of VT or VF is increased as the weight percentage of ischemia area goes up.

Animals↗
PubMed1992

[The operation treatment for the age-related macular degeneration wet-type eyes and its complications].

Age-related macular degeneration (AMD) is one of the important causes for blindness in elderly population. The effect of the treatments by laser and vitrectomy in AMD wet-type eyes, which subretinal neovascularization is existed in or have vitreous hemorrhage, is reported and discussed. Using laser photocoagulation, 65% of the affected eyes had marked cicatrization and 31% were partially improved. Among the 4 AMD eyes with vitreous hemorrhage, three cases were successful after vitrectomy. It has a certain significance for rescuing the vision and controlling the development in AMD wet-type eyes.

Aged↗
PubMed1992

[Effect of 764-3 on histamine content in the lungs during inflammation and on the proliferation of lung fibroblasts].

The changes of histamine content in inflamed lungs induced by bleomycin, lung fibroblast proliferation enhanced by histamine and the effect of 764-3 on these parameters were investigated. Results showed that: 1) after intratracheal instillation of bleomycin for 7 and 21 days, the lung histamine content increased significantly, and 764-3 inhibited this increase of histamine content; 2) histamine enhanced the proliferation of lung fibroblasts in a dose- and time-dependent manner, and 764-3 inhibited the proliferation of lung fibroblasts in both normal and histamine-enhanced conditions. Results suggested that both inhibitory actions (direct inhibition of fibroblast proliferation and indirect action stemming from a reduction in the histamine content increase) might be involved in the antifibrotic mechanism of 764-3.

Animals↗
PubMed1992

[Preparation of liposomes entrapping plasmid DNA and linear DNA].

Liposomes entrapping plasmids pSV2-neo DNA, pUC18-ras DNA, pSV2-neo-ras DNA and linear DNA were prepared. The liposomes were composed of DOPC/Chol/OA (4:4:3) and pH-sensitive DOPE/Chol/OA (4:4:3), respectively. The efficiency of DNA entrapment was about 50%. Gel electrophoresis analysis showed: Liposome-entrapped DNA was not digested by DNase; The entrapped DNA molecules were intact and stable for at least 5-6 months at 4 degrees C. During preparation of pH-sensitive liposome, the pH must be kept at 8.0.

DNA↗
PubMed1992

[Screening and distinguishing heavy chain variable region genes of McAb against encephalitis type B virus].

In order to prepare human-mouse chimeric antibody against encephalitis type B virus, hybridoma 51-8 cells secreting monoclonal antibody against the virus were used as material for isolating heavy-chain variable region gene of the McAb. High molecular weight DNA of the hybridoma cell was partially digested by BamHI, and then constructed a gene library containing 2 x 10(7) pfu with lambda EMBL-3 as vector. With cDNA of heavy-chain variable region of the monoclonal antibody as probe, nine positive plaques were screened from 360,000 plaques, which have been proven that they contained a fragment of heavy-chain variable region genes by dot hybridization and Southern hybridization. Four recombinants among the nine positive plaques were further distinguished with J11 probe containing J3, J4 and heavy-chain enhancer. After cutting by EcoR1, there was a 3.8 kb fragment in three recombinants as similar to that in liver cell and Sp2/0 cell, but not in the fourth recombinant (lambda 8a4) which contained a 4.5 kb fragment that did not present in liver cell and Sp2/0 cell. The results showed that the inserts in former 3 recombinants were non-rearranged fragment of heavy-chain variable region genes, but the insert in lambda 8a4 contained a rearranged functional variable region gene. The 4.5 kb fragment could not be hybridized with a probe containing J1 and J2, but contained VH, J3 or/and J4 and enhancer, that further proved it was a functional variable region gene. Therefore, the 4.5 kb fragment was isolated and subcloned in pUC 19, and its physical map was made.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Rotavirus infection of the oropharynx and respiratory tract in young children.

Oropharyngeal aspirates were obtained from 89 infants hospitalized with respiratory illnesses accompanied or not by diarrhea and 33 control patients without the diseases. Rotavirus was detected from 25 of these patients by immunocytology, isolation of the virus in cultures of MA104 cells, or both. None of the control patients gave a positive result. The infection involves squamous cells and globlet cells probably originating from the oropharynx, and ciliated columnar epithelial cells from the respiratory tract. The virus from 2 specimens was propagated by repeatedly passaging in the cultures and found to have characteristic morphology of rotavirus. The electrophoretic patterns of the viral RNA extracted from them are closely similar to those obtained with the rotavirus genome extracted from the stool of the same patients. Repeated stool specimens were also obtained, and sera were paired from some of these subjects. All but one of the patients who gave a positive virology for their aspirates also showed a significant rise in the titres of common group A rotavirus antibody, neutralizing antibody against one or more of serotypes of rotavirus, or both. Patients who excreted rotavirus in their stools were younger and had significantly lower titres of rotavirus antibodies in their acute sera, than those who shedded the virus in the oropharynx but did not excrete the virus in repeated stool specimens. The prevalence of rotavirus in the oropharyngeal aspirates from these patients surpassed that of adenovirus, respiratory syncytial virus, influenza virus, and herpes simplex virus combined.

Antibodies, Viral↗
PubMed1991

Fanconi anemia: evidence for linkage heterogeneity on chromosome 20q.

Fanconi anemia is a rare autosomal recessive disorder in which affected individuals are predisposed to acute myelogenous leukemia and other malignancies. We report the results of a genetic linkage study involving 34 families enrolled in the International Fanconi Anemia Registry. A significant lod score was obtained between D20S20, an anonymous DNA segment from chromosome 20q, and Fanconi anemia (Zmax 3.04, theta max = 0.12). However, six other anonymous DNA segments from chromosome 20q, including D20S19, which is highly polymorphic and tightly linked to D20S20, showed no or only weak evidence for linkage to Fanconi anemia. An admixture test revealed significant evidence for linkage heterogeneity (chi 2 = 6.10, P = 0.01) at the D20S19 locus. Lod scores suggestive of linkage between Fanconi anemia and this locus were obtained with two of the largest kindreds studied (lods = 2.6 and 2.1, at theta = 0.001). Thus, our data support the provisional assignment of a Fanconi anemia gene to chromosome 20q.

Chromosome Mapping↗
PubMed1991

[Protective effects of apolipoprotein CII on endothelial cell injury induced by low density lipoprotein].

Human umbilical vein endothelial cells (EC) were cultured. The protective effects of high density lipoprotein (HDL) and apolipoprotein CII (apoCII) on the morphology and function of EC injured by low density lipoprotein (LDL) were studied by observing the morphological changes with phase-contrast and transmission electron microscopy, measuring the release of lactate dehydrogenase (LDH) and secretion of 6-Keto-prostaglandin F1 alpha. The EC injured by LDL showed cell contraction, membrane damage, increased release of LDH and decreased secretion of PGI2. When HDL or apoCII was added to culture media before LDL addition, the EC showed normal morphology, normal LDH release and PGI2 synthesis. The results indicated that both HDL and apoCII can resist the injurious effect of LDL on cultured EC and that apoCII as well as HDL may play an important role in combating atherogenesis.

6-Ketoprostaglandin F1 alpha↗