Biomedical subjects

D Tang

Publications and source records attributed to D Tang.

At least 37 records · Page 2Linked to original sources

PubMed2001

Comparison of photovoltaic behaviors for horseradish peroxidase and its mimicry by surface photovoltage spectroscopy.

Surface photovoltage spectroscopy (SPS) was chosen to study the photovoltaic behavior of horseradish peroxidase (HRP), hemin and immobilized hemin (poly(NIPAAm/MBA/hemin)). Different photovoltaic behaviors were observed in these three systems. In air, similar SPS curves were found for HRP and poly(NIPAAm/MBA/hemin) with different response intensities. However, poly(NIPAAm/MBA/hemin) showed a wider changing range upon increasing the positive and negative bias to 1.0 V. The SPS of hemin showed a total different behavior when an external positive potential was applied. In vacuum, clearly different photovoltaic behaviors were found. Moreover, the response value decreased when HRP was exposed to O2, the SPS intensity was different from that in air, and could be altered by changing the external biases. On the other hand, the SPS could not be changed before and after poly(NIPAAm/MBA/hemin) was exposed to O2. These differences may result from different chemical microenvironments for hemin in HRP versus that in poly(NIPAAm/MBA/hemin). It could be concluded that H2O and O2 were important factors affecting the photovoltage response in HRP, but only H2O played this important role in poly(NIPAAm/MBA/hemin).

Horseradish Peroxidase↗

PubMed2001

Negative regulation of defense responses in plants by a conserved MAPKK kinase.

The enhanced disease resistance 1 (edr1) mutation of Arabidopsis confers resistance to powdery mildew disease caused by the fungus Erysiphe cichoracearum. Resistance mediated by the edr1 mutation is correlated with induction of several defense responses, including host cell death. Double mutant analysis revealed that all edr1-associated phenotypes are suppressed by mutations that block salicylic acid (SA) perception (nim1) or reduce SA production (pad4 and eds1). The NahG transgene, which lowers endogenous SA levels, also suppressed edr1. In contrast, the ein2 mutation did not suppress edr1-mediated resistance and associated phenotypes, indicating that ethylene and jasmonic acid-induced responses are not required for edr1 resistance. The EDR1 gene was isolated by positional cloning and was found to encode a putative MAP kinase kinase kinase similar to CTR1, a negative regulator of ethylene responses in Arabidopsis. Taken together, these data suggest that EDR1 functions at the top of a MAP kinase cascade that negatively regulates SA-inducible defense responses. Putative orthologs of EDR1 are present in monocots such as rice and barley, indicating that EDR1 may regulate defense responses in a wide range of crop species.

Amino Acid Sequence↗

PubMed2001

Timing cell-cycle exit and differentiation in oligodendrocyte development.

During animal development many cells permanently stop dividing and terminally differentiate. For the most part, the mechanisms that control when the cells exit the cell cycle and differentiate are not known. We have been studying the mechanisms in the oligodendrocyte cell lineage. Studies of oligodendrocyte precursor cells (OPCs) in culture suggest that each OPC has a built-in timing mechanism that helps determine when the cell stops dividing and differentiates. This intrinsic timer consists of at least two components--a timing component, which measures elapsed time, and an effector component, which stops cell division and initiates differentiation at the appropriate time. The timer seems to involve both transcriptional and posttranscriptional mechanisms, with some proteins progressively increasing and others progressively decreasing over time.

Animals↗

PubMed2001

Glutathione transport in human retinal pigment epithelial (HRPE) cells: apical localization of sodium-dependent gsh transport.

The study was undertaken to identify and localize GSH transport in non-transformed cultured human retinal pigmented epithelial cells (HRPE). In confluent monolayers exhibiting high transepithelial resistance (TER 700-1000 Omega cm(-2)), apical and basolateral GSH uptake were determined after introducing(35)S-GSH (+ 1 m M GSH) to the apical side or basal side in NaCl (Na+ -containing) or choline chloride (Na+ -free) buffers. Cells in growth medium or in incubation buffers were pretreated with acivicin to inhibit gamma-glutamyltranspeptidase (GGT). GSH efflux was measured after labelling the intracellular GSH pool by incubation overnight with 35 S-cysteine and quantitating the release of labelled GSH into the medium. Uptake of GSH was found at both the apical and basolateral membranes of HRPE cells. Inhibition of gamma-glutamyltranspeptidase (GGT) with acivicin did not alter mean GSH uptake (nmol per million cells per 30 min) significantly at the apical (1.63 +/- 0.32 vs 1.45 +/- 0.30; with and without acivicin respectively) or the basolateral (1.17 +/- 0.21 vs 1.44 +/- 0.38) membranes. Transport was verified to be in the form of intact GSH by HPLC. Uptake was unaffected by the removal of Na+ at the basolateral membrane while apical uptake exhibited partial but significant (approximately 40%) Na+ -dependency. Net GSH efflux (nmol per million cells per min) to the apical side of HRPE cells was higher than to the basolateral side in the presence of sodium. Transepithelial flux in the basolateral to apical direction was approximately 17-fold higher than the apical to basolateral direction resulting in a net flux of GSH to the apical side. In conclusion, HRPE cells exhibit GSH transport by Na+ -dependent and Na+ -independent mechanisms. The Na+ -dependent GSH transporter is localized to the apical membrane of HRPE cells.

Biological Transport↗

PubMed2001

Expressional profiling of genes related to pollination and fertilization in rice.

Pollination and fertilization are key steps leading to seed and fruit formation. To obtain genes involved in pollination and fertilization in rice, an RNA fingerprinting technique, cDNA-AFLP (amplified fragment length polymorphism), was used to generate transcript profiles related to pollination. Of 15,000 cDNA fragments inspected, 2,100 showed altered expression in the pollinated pistil, of which about 1/5 were up-regulated (URP) and the rest down-regulated (DRP), suggesting that gene repression is a predominant mode of gene regulation in the pollinated pistil. Over 200 URP genes were sequenced and databank searches revealed that 70% of them represented previously unnoticed rice genes. DNA blot analysis of 20 URP genes detected no restriction fragment length polymorphisms (RFLP) between two relatively distant rice varieties, suggesting that the URP genes are highly conserved and likely play important roles in pollination and fertilization. Furthermore, two genes, URP47 and URP63, probably encoding an ADP-ribosylation factor and a membrane transporter, respectively, in relation to pollination were discussed.

DNA, Plant↗

PubMed2001

Steady flow and wall compression in stenotic arteries: a three-dimensional thick-wall model with fluid-wall interactions.

Severe stenosis may cause critical flow and wall mechanical conditions related to artery fatigue, artery compression, and plaque rupture, which leads directly to heart attack and stroke. The exact mechanism involved is not well understood. In this paper a nonlinear three-dimensional thick-wall model with fluid-wall interactions is introduced to simulate blood flow in carotid arteries with stenosis and to quantify physiological conditions under which wall compression or even collapse may occur. The mechanical properties of the tube wall were selected to match a thick-wall stenosis model made of PVA hydrogel. The experimentally measured nonlinear stress-strain relationship is implemented in the computational model using an incremental linear elasticity approach. The Navier-Stokes equations are used for the fluid model. An incremental boundary iteration method is used to handle the fluid-wall interactions. Our results indicate that severe stenosis causes considerable compressive stress in the tube wall and critical flow conditions such as negative pressure, high shear stress, and flow separation which may be related to artery compression, plaque cap rupture, platelet activation, and thrombus formation. The stress distribution has a very localized pattern and both maximum tensile stress (five times higher than normal average stress) and maximum compressive stress occur inside the stenotic section. Wall deformation, flow rates, and true severities of the stenosis under different pressure conditions are calculated and compared with experimental measurements and reasonable agreement is found.

Aortic Valve Stenosis↗

PubMed2001

Modeling of bottom backscattering from three-dimensional volume inhomogeneities and comparisons with experimental data.

In this paper, backscattering from 3D volume inhomogeneities in the seabed is modeled and the results compared with experimental data at 250-650 Hz. The experiment was part of the Acoustic Reverberation Special Research Program (ARSRP) and the data were obtained in a sediment pond on the western flank of the Mid-Atlantic Ridge. A volume scattering model based on first-order perturbation theory is developed incorporating contributions from both sound speed and density fluctuations. With the propagators, i.e., the Green's functions, handled accurately through numerical wave number integration and random fluctuations generated effectively by a new scheme modified from the spectral method, the model is capable of simulating monostatic, backscattered fields in the frequency domain as well as in the time domain owing to 3D volumetric sediment inhomogeneities. The model compares favorably and consistently with the ARSRP backscattering data over the entire frequency band, with the fluctuations of sound speed and density in two irregular sediment layers, identified from the data analysis, described by a power-law type of power spectrum.

Journal Article↗

PubMed2001

Anthropophobia: its meaning and concomitant experiences.

This study investigated the essential feature and concomitant experiences of anthropophobia, a culturally specific phobic disorder in China and Japan. One hundred and fifty subjects, including 50 anthropophobic, 50 neurasthenic and 50 normal subjects, were recruited from hospitals and downtown residential areas in Beijing. Measures of anthropophobic symptoms and DSM-III-R depressive and anxiety symptoms were administered to all subjects. Nonparametric analysis of variance, analysis of variance (ANOVA and MANOVA) and Fisher's exact test were performed to examine group differences on each symptomatic item of the three measures. Results indicate that the core anthropophobic symptoms include a fear of making eye contact with others and a fear of being watched by others, which essentially express fears of others' judgement or opinion of oneself. Anxiety and depression are associated features of anthropophobia. However, these concomitants are experienced more cognitively and less somatically in the case of anthropophobia than neurasthenia.

Adult↗

PubMed2001

[Acidity and acid buffering capacity of aerosols during sand-dust storm weather in Beijing].

In the spring of 2000, there were 12 sand-dust storms in Beijing. 2 sand-dust storms were experienced in time and mass concentrations, elementary concentrations acidity and acidic buffering capacity of TSP(Total Suspended Particulate, < 100 microns) and PM10(Inhalable particulate, < 10 microns) were sampled and analyzed. Results showed that pollution level of aerosols was extremely high. However, the acidity of aerosols was relatively low and the aerosols had very strong acid buffering capacity for acidification. Therefore, the aerosols brought about by the sand-dust storms could avoid the occurrence of acidic precipitation to some extent.

Acids↗

PubMed2001

Neuronal cdc-2 like kinase in developing kindling rat hippocampus.

OBJECTIVE: To test the hypothesis that neuronal cdc2-like kinase (Cdk5/p35nck5a) plays an important role in neuronal maturation and sprouting. METHODS: Changes kinase activity, expression levels and subcellular localizations of Cdk5 and p35nck5a in the rat hippocampus were studied during kindling progression by Western blot analysis, immunohistochemistry, immunoprecipitation and kinase assay. RESULTS: Kinase activity in kindling rats was significantly higher than that in normal adult rats. The kinase activity at stage 3 was most prominent among all stages of kindling progression. The changes in kinase activity coincided with those of p35nck5a expression in kindling rats. In contrast, the expression of Cdk5 was constant throughout the progression of kindling stages. However, subcellular localization of Cdk5 dramatically changed in the hippocampal neurons of kindling rats. Cdk5 was translocated from axon to soma when kinase activity was high. p35nck5a was always localized in the soma throughout kindling progression. CONCLUSIONS: Neuronal cdc2-like kinase plays an important role in synaptic reorganization, and the translocation of Cdk5 to the soma from the axon may be a novel regulatory mechanism to control kinase activity.

Animals↗

PubMed2001

[Microsatellite instability in renal cell carcinoma and its mechanisms].

OBJECTIVE: To study the expression of microsatellite instability (MSI) in renal cell carcinoma (RCC) and its relationship with gene mutation. METHODS: Tumor samples from 34 patients with RCC were analyzed for MSI by PCR. RT-PCR was used to evaluate the expression of mRNA of 5 human mismatch repair (MMR) genes in RCC and RCC cell lines. Mutation of hMLH1 gene coding regions was detected by PCR-SSCP. PCR was used to check the mutations of TGF-beta R II gene and BAX gene in 15 MSI-positive samples of RCC. RESULTS: Microsatellite changes were detected in 15 of 34 patients with RCC (44.1%). It might be associated with the progression of this disease. There were 3 of 15 MSI-positive RCC cases without expression of MMR gene hMLH1, and in 3 of 15 cases its expression was decreased. All 5 MMR genes were expressed in normal and RCC 949 cell line. There were three mutations in 15 MSI-positive cases. Frame shift mutation of TGF beta R II gene and BAX gene was found in 6 and 4 of the 15 cases with MSI, respectively, but it was not found in MSI-negative RCC and normal tissue. CONCLUSION: MSI and expression of MMR genes are associated events in RCC. The effect of gene mutation on tumorgenerasis may be related to MSI.

Adaptor Proteins, Signal Transducing↗

PubMed2001

[Correlation of p16 mutation and biological behavior in Chinese laryngeal cancer].

OBJECTIVE: To investigate the correlation between p16 gene mutation and laryngeal cancer biological behavior as well as its prognosis in laryngeal cancer. METHOD: 24 specimens of primary laryngeal cancer and 10 speciments with benign lesion in larynx were examined for mutations in exon2 of p16 by using PCR-SSCP silver stainning technique. RESULT: Mutations frequency of laryngeal cancer was 62.5% (15/24). Nothing was found in 10 cases with laryngeal benign lesion. CONCLUSION: There is a strong correlation between p16 gene mutation and the biological behavior of chinese laryngeal cancer, such as histologic differentiation, invasion stage, and regional lymph nodes metastasis (P < or = 0.05). PCR-SSCP silver stainning technique is one of the most sensitive and simplest measure for detecting genetic mutation. It is worth using in clinical laboratory because of its readiness, repetition and lower cost.

Genes, p16↗

PubMed2001

[Relationship between computerized cardiotocography and perinatal outcomes].

OBJECTIVE: To analyze the relationship between the parameters of computerized cardiotocography (CTG) and perinatal outcomes. METHODS: Three hundred and eight CTG examination in 190 third trimester pregnancy were performed, 46 cases in antepartum, 262 cases in intrapartum. CTG parameters including: baseline fetal heart rate (BHR), the square root of the mean squared differences (RMSSD), the proportion derived by dividing the number of differences greater than 3 beats/min by the total number (NN50), acceleration (AC), deceleration (DC), amplitude of deceleration (AMP), duration of deceleration from BHR to bottom (T1) and duration from bottom to BHR (T2), the ratio of T2 to T1 (T2/T1), square of deceleration (DS), the ratio of AMP to duration of deceleration (H/T), the ratio of DS to the product of AMP multiplied deceleration duration (S/HT), amplitude of uterine contraction (UTAMP), number of uterine contraction (UTNO), duration of uterine contraction (UTDUR), square of uterine contraction (UTS), the ratio of AMP to UTAMP (HR/HU), the ratio of DS to UTS (SR/SU), the ratio of DS to UTAMP (SR/HU). After childbirth record neonatal Apgar scores, amniotic fluid colour (COL) and volume (VOL), umbilical cord arteria blood gas analysis. RESULTS: (1) The fetal heart rate (FHR) baseline and variability . In antepartum, there were significantly relationship between BHR and Apgar (r = 0.460, P < 0.01), RMSSD and COL (r = - 0.389, P < 0.05), NN50 and COL (r = - 0.368, P < 0.05), RMSSD and actual base excess (ABE) (r = 0.904, P < 0.05), NN50 and ABE (r = 0.919, P < 0.05), AC and ABE (r = 0.943, P < 0.05), BHR and SO2 ( r = - 0.895, P < 0.05). But during intrapartum, there were no significantly relationship between the baseline and variability of CTG with the Apgar scores, the quality and color of amniotic fluid, and the indexes of blood gas analysis of umbilical artery blood. (2) The deceleration of FHR. During antepartum there were significantly relationship between Apgar and AMP (r = - 0.472, P < 0.05), Apgar and H/T (r = - 0.526, P < 0.05), COL and AMP (r = 0.447, P < 0.05), COL and H/T (r = 0.543, P < 0.05) . During intrapartum the relationship of COL and T1 was significant (r = - 0.205, P < 0.05), there were significantly relationship between PH and H/T (r = 0.386, P < 0.05), ABE and H/T (r = 0.367, P < 0.05), Apgar and UTDUR (r = 0.149, P < 0.05), Apgar and UTS (r = 0.148, P < 0.05), PO2 and UTS (r = 0.234, P < 0.05), PO2 and UTNO (r = -0.246, P < 0.05), HCO3 and UTAMP (r = - 0.265, P < 0.05), TCO2 and UTAMP (r = - 0.268, P < 0.05), HCO3 and HR/HU (r = 0.385, P < 0.01), TCO2 and HT/HU (r = 0.385, P < 0.01), ABE and HR/HU (r = 0.323, P < 0.05). CONCLUSIONS: In antepartum, the baseline and variability of FHR play a more important role in predicting prenatal outcome than any other parameters; during intrapartum deceleration become more important, but with the affect by uterin contraction, the ratio of HR/HU may be useful during intrapartum.

Amniotic Fluid↗

PubMed2000

Sensitive determination of dissolved sulfide in estuarine water by solid-phase extraction and high-performance liquid chromatography of methylene blue.

A sensitive method involving solid-phase extraction and HPLC analysis of methylene blue has been developed to measure nanomolar levels of dissolved sulfide in oxic surface waters. The procedure included 1) a preconcentration step, in which methylene blue generated from sulfide reaction with n,n-dimethyl-p-phenylenediamine in acidic conditions in the presence of ferric ion was absorbed onto Waters tC18 cartridge; and 2) a determination step, in which methylene blue was separated by HPLC in a gradient elution to minimize natural organic matter interference and detected by absorbance. The concentrations of the dissolved sulfide, quantified by standard addition, were about 2.1-4.7 nM in oxic surface waters from Galveston Bay, Texas.

Chromatography, High Pressure Liquid↗

PubMed2000

Recruitment of the Arp2/3 complex and mena for the stimulation of actin polymerization in growth cones by nerve growth factor.

The growth of axons and dendrites during development and regeneration is regulated by cues in the environment. Many of these cues regulate the actin cytoskeleton of the protrusive structures (like filopodia) of the growth cone that are essential for detecting and responding to cues. Nerve growth factor, which promotes the formation of protrusive structures, stimulated actin polymerization in rat sympathetic growth cones, resulting within 1-2 min in accumulations of F-actin at the distal edge and in splotches of F-actin farther back. We examined the potential involvement of a protein machinery important in at least certain types of actin polymerization in non-neuronal cells. Members of the Arp2/3 complex, p34-Arc and p21-Arc, heavily concentrated in the early accumulations of F-actin, as did one member of the Ena/VASP family (Mena) but not another (VASP). Retention of Arc proteins at preferred sites of actin polymerization did not require polymerization itself. Growth cones of differentiated PC12 cells were similar to sympathetic growth cones in their response to NGF. Introduction into these cells of a peptide that should block the binding of Ena/VASP family proteins to the protein complex at sites of actin polymerization reduced the formation of splotches and filopodia in response to NGF. These results point to the early involvement of the Arp2/3 complex and the Ena/VASP family in growth factor-stimulated actin polymerization that gives rise to protrusive structures at the growth cone.

Actin-Related Protein 2↗

PubMed2000

Caspase-8 activation and bid cleavage contribute to MCF7 cellular execution in a caspase-3-dependent manner during staurosporine-mediated apoptosis.

There are at least two distinct classes of caspases, initiators (e.g. caspases-8, -9, and -10) and effectors (e.g. caspase-3). Furthermore, it is believed that there are two distinct primary apoptotic signaling pathways, one of which is mediated by death receptors controlled by caspases-8/10, and the other by the release of cytochrome c and activation of a caspase-9/Apaf1/cytochrome c apoptosome. However, several recent reports have demonstrated that caspase-8, and its substrate Bid, are frequently activated in response to certain apoptotic stimuli in a death receptor-independent manner. These results suggest that significant cross-talk may exist between these two distinct signaling arms, allowing each to take advantage of elements unique to the other. Here we provide evidence that activation of caspase-8, and subsequent Bid cleavage, does indeed participate in cytochrome c-mediated apoptosis, at least in certain circumstances and cell types. Furthermore, the participation of activated caspase-3 is essential for activation of caspase-8 and Bid processing to occur. Although caspase-8 activation is not required for the execution of a cytochrome c-mediated death signal, we found that it greatly shortens the execution time. Thus, caspase-8 involvement in cytochrome c-mediated cell death may help to amplify weaker death signals and ensure that apoptosis occurs within a certain time frame.

Apoptosis↗

PubMed2000

GSH transport in human cerebrovascular endothelial cells and human astrocytes: evidence for luminal localization of Na+-dependent GSH transport in HCEC.

The purpose of the present study was to identify and localize glutathione (GSH) transport in an in vitro tissue culture model of blood-brain barrier (BBB). The localization of Na+-dependent GSH transport in an immortalized cell line of human cerebrovascular endothelial cells (HCEC) and asymmetry of transport in Transwell studies were investigated. Initial studies with cultured HCEC established a significant (45%) Na+-dependency for GSH uptake in cultured HCEC pretreated with acivicin, an inhibitor of gamma-glutamyltranspeptidase (GGT). Transendothelial electrical resistance (TEER) and uptake of [35S]GSH from luminal and abluminal fluids of HCEC were measured in Na+-containing and Na+-free (choline chloride) buffers using cells grown on gelatin-coated membrane filters. TEER of HCEC monolayers in regular medium was 40.1 +/- 8.0 ohms cm2. Human astrocyte-conditioned medium (ACM) caused no change in TEER, but increased GGT activity approximately threefold when measured in cell lysates. Luminal and abluminal GSH uptake increased in a time-dependent fashion and were not affected by inhibition of GGT activity with acivicin. Sodium dependency was only observed for luminal uptake (Na+-containing 2.41 +/- 0.15 vs. Na+-free 0.96 +/- 0.03 pmol/30 min/million cells, p < 0.001) but not for abluminal uptake (1.02 +/- 0.13 vs. 1.11 +/- 09, p > 0.05). Apparent efflux via the luminal membrane was lower in the presence of sodium as compared to that without sodium, further suggesting that a Na+-dependent uptake process for GSH is operative at this membrane. GSH uptake and efflux were also demonstrated in neonatal rat and fetal human astrocytes, both exhibiting partial Na+-dependency of uptake. In conclusion, our results show for the first time, that HCEC and astrocytes take up GSH by both Na+-dependent and -independent mechanisms. The Na+-dependent GSH transport process in HCEC appears to be localized to luminal plasma membranes of HCEC.

Animals↗

PubMed2000

Bundling of microtubules in the growth cone induced by laminin.

Axons growing in the developing nervous system are guided by cues in the environment which act at the growth cone. So far, the initial cytoskeletal target of these cues has been found to be the network of actin filaments in the peripheral region of the growth cone. Laminins are constituents of the extracellular matrix which promote axonal growth. They exert effects on the actin network. Here, laminin 1 is shown to affect microtubules as well. Acute addition of laminin 1 to rat sympathetic neurons quickly caused the advance of microtubules and their bundling within the initial widely spread growth cone and then the outgrowth of thin, rapidly growing nascent axons. The bundling was pharmacologically separable from the advance of microtubules caused by laminin, as the former but not the latter was blocked by lithium. The bundling did not depend on the peripheral network of actin filaments, as it was unimpaired by the removal of this network with cytochalasin D. Thus, microtubules seem to be a direct cytoskeletal target for laminin 1 in the growth cone, with important consequences for axonal outgrowth.

Actin Cytoskeleton↗