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C Yu

Publications and source records attributed to C Yu.

At least 271 records · Page 15Linked to original sources
PubMed1997

The study on the relationship between the expression of calponin and gallstone formation.

In order to understand the molecular mechanisms of gallstone formation, the expression of calponin in animal model of gallstone disease was studied. High-cholesterol diet was given to the guinea pigs to induce gallstone formation. RT-PCR and Western-blotting were used to evaluate expression level of calponin gene. Down-regulation of calponin gene expression was observed in animals with gallstone, while myosin expression was relatively stable. Our results indicated that the decrease of calponin could increase the pressure of Oddi's sphincter, aggravate the stasis of bile and promote the gallstone formation.

Animals↗
PubMed1997

In vivo radioprotective effect of AcSDKP on canine myelopoiesis.

The tetrapeptide acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) interferes with G1/S-phase progression, and the resulting cell cycle arrest is thought to protect hematopoietic stem cells against injury by cycle-active cytotoxic agents. We investigated the radioprotective effect of AcSDKP in a canine radiation model. Dogs were given total-body irradiation (TBI) at an exposure rate of 10 cGy/min, either without further therapy (control) or with administration of AcSDKP at 0.05-500 micrograms/ kg/24 h beginning before and continuing until after completion of TBI. At 400 cGy of TBI, one of 28 control dogs and one of eight AcSDKP-treated dogs recovered hematopoiesis (p = 0.40). At 300 cGy, seven of 21 control dogs recovered hematopoiesis compared with five of five AcSDKP-treated dogs (p = 0.01). In dogs given 300 cGy and AcSDKP, the granulocyte nadirs were less profound (p = 0.04) and occurred later (p = 0.04) than among controls; platelet kinetics did not differ. These data suggest, therefore, that AcSDKP provides a radioprotective effect in dogs exposed to 300 cGy TBI. Such an effect might be beneficial in recipients of intensive radiation therapy. Conceivably, the effect on hematopoietic recovery could be amplified by growth factor administration after irradiation.

Animals↗
PubMed1997

Cortical end-stopped perceptive fields: evidence from dichoptic and amblyopic studies.

Psychophysical length and width spatial interactions associated with a line target were measured in normal observers dichoptically and in observers with naturally acquired amblyopia to investigate the neural locus of end-stopped perceptive fields. Results show (1) interocular transfer of psychophysical end-stopping, flank-inhibition, and length and width summation; and (2) severe, but significantly different, loss of end-stopping and flank-inhibition in the central visual fields of amblyopic eyes. Together, these results suggest a cortical basis for end-stopped perceptive fields, and that psychophysical end-stopping and flank-inhibition are a consequence of distinct cortical inhibition. The damaging effects of amblyopia on end-stopping and flank-inhibition are weaker and less different from each other under transient conditions. Our results provide further evidence supporting the suggestion that end-stopped perceptive fields are the psychophysical analogs of cortical end-stopped receptive fields.

Adult↗
PubMed1997

Cortical components of the Westheimer function.

The Westheimer function in human cone vision was measured in normal observers under dichoptic conditions and in observers with naturally acquired amblyopia. Results show interocular transfer of both desensitization and sensitization under either "sustained" or "transient" stimulus conditions if binocular rivalry is eliminated. The spatial sensitization branches of the amblyopic functions are considerably broadened as compared with those of the non-amblyopic function. Our results are consistent with cortical components for the Westheimer function which probably reflect the behavior of cortical spatial filters.

Adult↗
PubMed1997

Spatial facilitation predicted with end-stopped spatial filters.

We examined the role of putative end-stopped spatial filters in determining spatial facilitation associated with a line target flanked by square inducers. Results obtained in normal and amblyopic observers were well predicted by end-stopping and other receptive field features of end-stopped spatial filters revealed in a modified Westheimer paradigm. The role of target-inducer collinearity, the effects of inducer polarity, and facilitation associated with non-orientational circular targets, were also studied. Our results suggest that spatial facilitation results from antagonism surrounding spatial filter centers, with end-stopping playing a prominent role.

Adult↗
PubMed1997

Specificity of helix-induction by 2,2,2-trifluoroethanol in polypeptides.

The specificity of helix-induction in polypeptides by 2,2,2-trifluoro ethanol (TFE) is studied using an all beta-sheet protein such as cardiotoxin analogue I (CTX I) from the Taiwan Cobra (Naja naja atra) and a homopolymer such as poly-L-lysine. It is found that alcohols including TFE can 'non-specifically' induce helix at high concentrations both in CTX I and polylysine at neutral pH. However, among the alcohols used, only TFE could transform the heat-induced beta-sheet conformation of polylysine at pH 11.5 into an alpha-helix. The beta-sheet to alpha-helix conversion in polylysine (in the beta-sheet conformation) occurs even at very low concentrations of TFE (< 5% v/v). In addition, experiments on the effect(s) of TFE on the denatured and reduced CTX I (rCTX I) indicate the helix-induction in rCTX I takes place at low TFE concentrations (< 20% v/v). The results of this study hint at the possible influence of disulfide bridges on the induction of helix by TFE.

Amino Acid Sequence↗
PubMed1997

Acetonitrile-induced conformational transitions in poly-L-lysine.

The effect of acetonitrile on the random coil, alpha-helix and beta-sheet conformations induced in poly-L-lysine is studied. It is found that acetonitrile at higher concentrations transforms the backbone of polylysine from a random coil to a helical conformation. Addition of acetonitrile to polylysine (pH 11.5) in the alpha-helix conformation, induces conformational changes in two stages. At concentrations below 60% v/v, acetonitrile stabilizes the helical conformation and at higher concentrations (> 70% v/v), it destabilizes the helix. beta-sheet-->alpha-helix-->random coil conformational transitions are found to occur when polylysine in the heat-induced conformation is titrated with acetonitrile. The possible mechanism(s) of action of acetonitrile in inducing these structural transitions is discussed.

Acetonitriles↗
PubMed1997

The mechanism of 2,2,2-trichloroacetic acid-induced protein precipitation.

The mechanism of 2,2,2-trichloroacetic acid (TCA)-induced precipitation of proteins is studied. The TCA-induced protein precipitation curves are observed to be U-shaped. It is bound that the protein-precipitate-inducing effects of TCA are due to the three chloro groups in the molecule. Using cardiotoxin III (CTX III) isolated from the Taiwan cobra (Naja naja atra), as a model protein, we attempt to understand the molecular basis for the TCA-induced effects. Employing circular dichroism, proton-deuterium exchange in conjunction with conventional 2D NMR techniques, and 1-anilino naphthalene-8-sulfonate-binding experiments, we demonstrate that CTX III is in a partially structured state similar to the 'A state' in 3% w/v TCA. It is postulated that the formation of this 'sticky' partial structured 'A state' in the TCA-induced unfolding pathway is responsible for the acid-induced protein precipitation.

Chemical Precipitation↗
PubMed1997

Glucocorticoids fail to enhance the effect of FK506 and methotrexate in prevention of graft-versus-host disease after DLA-nonidentical, unrelated marrow transplantation.

Several steroid receptor-associated heat shock proteins can bind to FK506 as immunophilins. This has led to speculation that the steroid receptor and immunophilin signal transduction pathways are functionally interrelated. Indeed, in vitro work showed that FK506 treatment of intact L929 cells which were stably transfected with various reporter plasmids resulted in a potentiation of glucocorticoid hormone-induced glucocorticoid receptor-mediated gene transcription. These findings have raised the possibility of additive or synergistic immunosuppressive effects of FK506 and glucocorticoids. We tested this hypothesis in a canine model of GVHD prevention. Two groups of dogs were given 9.2 Gy total body irradiation followed by hematopoietic grafts from unrelated DLA-nonidentical donors. Among the first group of four recipients which were given FK506 and glucocorticoids, one rejected the graft, while three developed acute GVHD and died from associated complications between days 14 and 34. In the second group of nine recipients which were given FK506, glucocorticoids and methotrexate (MTX), only one dog became a long-term survivor while eight dogs died between days 21-114 with GVHD (n = 5) or FK506-associated toxicities (n = 3). Thus, addition of glucocorticoids to FK506 or FK506/MTX showed neither synergistic nor additive effects with respect to GVHD prevention in this model, and no survival advantages were seen compared to previously reported results with FK506 alone or FK506 and MTX in combination, respectively.

Animals↗
PubMed1997

Snake venom cardiotoxins-structure, dynamics, function and folding.

Snake cardiotoxins are highly basic (pI > 10) small molecular weight (approximately 6.5 kDa), all beta-sheet proteins. They exhibit a broad spectrum of interesting biological activities. The secondary structural elements in these toxins include antiparallel double and triple stranded beta-sheets. The three dimensional structures of these toxins reveal an unique asymmetric distribution of the hydrophobic and hydrophilic amino acids. The 3D structures of closely related snake venom toxins such as neurotoxins and cardiotoxin-like basic proteins (CLBP) fail to show similar pattern(s) in the distribution of polar and nonpolar residues. Recently, many novel biological activities have been reported for cardiotoxins. However, to-date, there is no clear structure-function correlation(s) available for snake venom cardiotoxins. The aim of this comprehensive review is to summarize and critically evaluate the progress in research on the structure, dynamics, function and folding aspects of snake venom cardiotoxins.

Amino Acid Sequence↗
PubMed1997

Proline is a protein solubilizing solute.

The effect of proline on the prevention of trichloroacetic acid (TCA)-induced protein precipitation is studied. It is found that proline at high concentrations (> 4.0 M) completely prevents TCA-induced precipitation of hen egg white lysozyme. Other osmolytes such as ethylene glycol, glycerol and sucrose fail to prevent the TCA-induced precipitation of lysozyme. Viscosity and 1-anilino-8-naphthalene sulphonic acid binding experiments suggest that proline at high concentration forms an ordered supramolecular assembly. Proline is shown to increase the solubility of protein due to formation of such higher order assemblies. A model of the supra-molecular assembly of proline is proposed and a possible in vivo role of the increased levels of proline under water stress is discussed.

Animals↗
PubMed1997

Extracranial radiation doses in patients undergoing gamma knife radiosurgery.

OBJECTIVE: To determine extracranial doses in patients undergoing gamma knife radiosurgery and identify component sources of the extracranial doses using phantom measurements. METHODS: The lateral canthi, thyroid, sternum, and midpelvis region were monitored in 104 unselected patients during their gamma knife treatments using thermoluminescent dosimetry. Measured doses were normalized to integral dose, equivalent time (which is defined in relation to the activity of the cobalt-60 sources), and collimator size to correlate radiation doses with these parameters. A phantom was constructed from a polystyrene sphere as a model of the head adjacent to thoracic and pelvic body sections from a commercial humanoid phantom. RESULTS: On average, 18 minutes of equivalent time and five isocenters were required to achieve the prescribed dose coverage. The median prescribed dose was 18 Gy. For the lateral canthi, thyroid, sternum, and pelvis, the median doses were 24, 20, 21, and 4 cGy, respectively. Normalization to equivalent time and collimator size was superior to other techniques. Phantom measurements supported the results from patient measurements and further refined estimates of component doses to extracranial sites. CONCLUSION: Doses to extracranial sites ranged from 1.5% of the prescribed dose for the lateral canthi to 0.2% for the pelvis. Doses to the sternum and pelvis were proportional to the duration of irradiation. Scatter radiation contributed more than 50% of the dose to the canthi and thyroid. Leakage radiation typically contributed 80 to 90% of the dose to the sternum and pelvis. Radiation during patient couch transit contributed little to the doses at the measured extracranial sites.

Adult↗
PubMed1997

Multimedia benchmarking analysis for three risk assessment models: RESRAD, MMSOILS, and MEPAS.

This paper is one in a series that describes results of a benchmarking analysis initiated by the Department of Energy (DOE) and the United States Environmental Protection Agency (EPA). An overview of the study is provided in a companion paper by Laniak et al. presented in this journal issue. The three models used in the study--RESRAD (DOE), MMSOILS (EPA), and MEPAS (DOE)--represent analytically-based tools that are used by the respective agencies for performing human exposure and health risk assessments. Both single media and multimedia benchmarking scenarios were developed and executed. In this paper, the multimedia scenario is examined. That scenario consists of a hypothetical landfill that initially contained uranium-238 and methylene chloride. The multimedia models predict the fate of these contaminants, plus the progeny of uranium-238, through the unsaturated zone, saturated zone, surface water, and atmosphere. Carcinogenic risks are calculated from exposure to the contaminants via multiple pathways. Results of the tests show that differences in model endpoint estimates arise from both differences in the models' mathematical formulations and assumptions related to the implementation of the scenarios.

Air Pollutants, Radioactive↗
PubMed1997

An overview of a multimedia benchmarking analysis for three risk assessment models: RESRAD, MMSOILS, and MEPAS.

Multimedia modelers from the United States Environmental Protection Agency (EPA) and the United States Department of Energy (DOE) collaborated to conduct a detailed and quantitative benchmarking analysis of three multimedia models. The three models--RESRAD (DOE), MMSOILS (EPA), and MEPAS (DOE)--represent analytically-based tools that are used by the respective agencies for performing human exposure and health risk assessments. The study is performed by individuals who participate directly in the ongoing design, development, and application of the models. Model form and function are compared by applying the models to a series of hypothetical problems, first isolating individual modules (e.g., atmospheric, surface water, groundwater) and then simulating multimedia-based risk resulting from contaminant release from a single source to multiple environmental media. Study results show that the models differ with respect to environmental processes included (i.e., model features) and the mathematical formulation and assumptions related to the implementation of solutions. Depending on the application, numerical estimates resulting from the models may vary over several orders-of-magnitude. On the other hand, two or more differences may offset each other such that model predictions are virtually equal. The conclusion from these results is that multimedia models are complex due to the integration of the many components of a risk assessment and this complexity must be fully appreciated during each step of the modeling process (i.e., model selection, problem conceptualization, model application, and interpretation of results).

Air Pollutants↗
PubMed1997

Erythroid-cell-specific properties of transcription factor GATA-1 revealed by phenotypic rescue of a gene-targeted cell line.

The zinc finger transcription factor GATA-1 is essential for erythropoiesis. In its absence, committed erythroid precursors arrest at the proerythroblast stage of development and undergo apoptosis. To study the function of GATA-1 in an erythroid cell environment, we generated an erythroid cell line from in vitro-differentiated GATA-1- murine embryonic stem (ES) cells. These cells, termed G1E for GATA-1- erythroid, proliferate as immature erythroblasts yet complete differentiation upon restoration of GATA-1 function. We used rescue of terminal erythroid maturation in G1E cells as a stringent cellular assay system in which to evaluate the functional relevance of domains of GATA-1 previously characterized in nonhematopoietic cells. At least two major differences were established between domains required in G1E cells and those required in nonhematopoietic cells. First, an obligatory transactivation domain defined in conventional nonhematopoietic cell transfection assays is dispensable for terminal erythroid maturation. Second, the amino (N) zinc finger, which is nonessential for binding to the vast majority of GATA DNA motifs, is strictly required for GATA-1-mediated erythroid differentiation. Our data lead us to propose a model in which a nuclear cofactor(s) interacting with the N-finger facilitates transcriptional action by GATA-1 in erythroid cells. More generally, our experimental approach highlights critical differences in the action of cell-specific transcription proteins in different cellular environments and the power of cell lines derived from genetically modified ES cells to elucidate gene function.

Animals↗
PubMed1997

End stopping and length tuning in psychophysical spatial filters.

Psychophysical spatial filters or channels are usually modeled after simple-cell receptive fields, although many cortical cells are end stopped and length tuned. Using psychophysical masking, we demonstrate an analog to receptive field end stopping and length tuning in psychophysical spatial filters tuned to a wide range of spatial frequencies. Specifically, masking is maximal when the mask is approximately 5-6 arcmin longer than the target but is reduced when the mask exceeds this length, consistent with the properties of end-stopped cells. The strength and the extent of psychophysical end stopping appear to be determined by filter's spatial-frequency tuning, but length tuning varies with target length. The latter implies that spatial filters tuned to the same spatial frequency could have different length tuning and that there is no fixed length-to-width ratio of the filter size. Phase effects suggest linear length summation but nonlinear psychophysical end stopping which suggest that both first- and second-order visual processing is involved in end-stopped spatial filters.

Adult↗
PubMed1997

[Quantitative analysis of cAMP and cGMP in the plasma, iris and aqueous humor in rabbits with high intraocular pressure].

OBJECTIVE: To study the relationship between the levels of cyclic adenosine monophosphate (cAMP), cyclic guanosine monophos-phate (cGMP) in the plasma, iris and aqueous humor and high intraocular pressure in rabbits. METHODS: The quantitative tests of cAMP and cGMP from rabbits were carried out by radioimmunoassay technique. RESULTS: The results showed that there were 72.81 +/- 7.67, 141.08 +/- 16.70 and 28.40 +/- 0.49 of cAMP (nmol/L), and there were 10.37 +/- 6.15, 35.64 +/- 7.02 and 12.90 +/- 0.61 of cGMP (nmol/L) in the plasma, iris and aqueous humor respectively. The levels of cAMP were higher than those in the same samples from the animals as controls (P < 0.01), while the levels of cGMP were less than controls (P < 0.01). CONCLUSION: High intraocular pressure may be significantly associated with the levels of cAMP and cGMP.

Animals↗