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S Yang

Publications and source records attributed to S Yang.

At least 361 records · Page 20Linked to original sources
PubMed1997

A role for the actin cytoskeleton of Saccharomyces cerevisiae in bipolar bud-site selection.

Saccharomyces cerevisiae cells select bud sites according to one of two predetermined patterns. MATa and MAT alpha cells bud in an axial pattern, and MATa/alpha cells bud in a bipolar pattern. These budding patterns are thought to depend on the placement of spatial cues at specific sites in the cell cortex. Because cytoskeletal elements play a role in organizing the cytoplasm and establishing distinct plasma membrane domains, they are well suited for positioning bud-site selection cues. Indeed, the septin-containing neck filaments are crucial for establishing the axial budding pattern characteristic of MATa and MAT alpha cells. In this study, we determined the budding patterns of cells carrying mutations in the actin gene or in genes encoding actin-associated proteins: MATa/alpha cells were defective in the bipolar budding pattern, but MATa and MAT alpha cells still exhibit a normal axial budding pattern. We also observed that MATa/alpha actin cytoskeleton mutant daughter cells correctly position their first bud at the distal pole of the cell, but mother cells position their buds randomly. The actin cytoskeleton therefore functions in generation of the bipolar budding pattern and is required specifically for proper selection of bud sites in mother MATa/alpha cells. These observations and the results of double mutant studies support the conclusion that different rules govern bud-site selection in mother and daughter MATa/alpha cells. A defective bipolar budding pattern did not preclude an sla2-6 mutant from undergoing pseudohyphal growth, highlighting the central role of daughter cell bud-site selection cues in the formation of pseudohyphae. Finally, by examining the budding patterns of mad2-1 mitotic checkpoint mutants treated with benomyl to depolymerize their microtubules, we confirmed and extended previous evidence indicating that microtubules do not function in axial or bipolar bud-site selection.

Actins↗
PubMed1997

Toxoplasma gondii expresses two distinct lactate dehydrogenase homologous genes during its life cycle in intermediate hosts.

Two Toxoplasma gondii genes were characterized that are differentially expressed during the parasite's life cycle. The genes named LDH1 and LDH2, respectively, encode polypeptides similar to the enzyme lactate dehydrogenase (LDH; L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) from a variety of organisms. They show 64.0% nucleotide identity in the coding region and both have an intron at the same relative position. The deduced amino acid sequences of LDH1 and LDH2 share 71.1% identity. LDH1 and LDH2 are most similar to an LDH of Plasmodium falciparum (46.5% and 48.5% amino acid identities, respectively). The mRNA of LDH2 was only detected in the bradyzoite stage, while the mRNA of LDH1 was detected in both the bradyzoite and tachyzoite stages. However, by isoelectric focusing and immunoblot analysis, only one LDH isoform was found to be expressed in each stage. Furthermore, the expression of a reporter gene carrying chloramphenicol acetyltransferase (CAT) coding sequence and the putative LDH2 promoter sequence was significantly up-regulated by growing parasites in tissue culture in media with alkaline pH (pH 8.2, a condition known to induce the expression of bradyzoite-specific antigens), while the expression of a CAT reporter construct carrying the putative LDH1 promoter sequence was down-regulated by similar treatment. These results indicate that LDH expression is developmentally regulated in T. gondii and suggest a possible correlation between stage conversion and alteration in carbohydrate or energy metabolism in this parasite.

Amino Acid Sequence↗
PubMed1997

Effects of L-arginine supplementation on human lymphocyte proliferation in response to nonspecific and alloantigenic stimulation.

BACKGROUND: L-Arginine has been described as a potential immunostimulant in vitro and in vivo. Excessive arginine, however, may be counterproductive. Data support the concept of minimal arginine requirements for normal lymphocyte proliferation, but the results of supplementation with pharmacologic doses of arginine have been contradictory. We hypothesized that excessive arginine supplementation might result in a blunting of normal immune responses of human lymphocytes in vitro. MATERIALS AND METHODS: Peripheral blood mononuclear and T-cells were isolated from normal human donors. Cells were cultured in complete media with various concentrations of L-arginine, L-ornithine, and glycine. Lymphocytes were then stimulated with PHA or alloantigens, and proliferation was determined by measuring [3H]thymidine incorporation. RESULTS: Lymphocyte proliferation was inhibited by L-arginine at pharmacologic doses. The effects were completely reversible. This inhibition could not be prevented by lymphocyte stimulation with IL-2. Lymphocyte proliferation was more sensitive to inhibition by lower doses of arginine when alloantigens from irradiated fresh tumor cells or allogeneic lymphocytes were the stimuli. Finally, lymphocytes showed variable sensitivity to inhibition of proliferation in response to mitogen when treated with L-ornithine (little to no effect) or L-arginine (consistent inhibition at high doses). Pharmacologic doses of L-arginine result in reversible inhibition of normal lymphocyte proliferation in response to both mitogen and alloantigen. This inhibition could not be blocked by interleukin-2. CONCLUSIONS: We conclude that caution should be exercised when recommending aggressive L-arginine supplementation as a possible method to reverse clinical immunosuppression caused by cancer, malnutrition, or trauma.

Arginine↗
PubMed1997

Induction of PreB cell apoptosis by 7,12-dimethylbenz[a]anthracene in long-term primary murine bone marrow cultures.

Numerous studies demonstrate that polycyclic aromatic hydrocarbons (PAH) suppress immunity by modifying the function of both B and T cells. Relatively few studies have assessed the effects of these common environmental chemicals on immature lymphocytes. In the present study, long-term primary bone marrow cultures were employed to investigate the effects of a prototypic PAH and aryl hydrocarbon receptor (AhR) agonist, 7,12-dimethylbenz[a]anthracene (DMBA), on immature B lymphocytes. In this system, immature preB cells are maintained in a supportive microenvironment provided by bone marrow stromal cells. Results presented here demonstrate that (1) exposure of primary bone marrow cultures to DMBA results in preB cell death by apoptosis; (2) notably low doses of DMBA (> or = 10(-8) M) induce preB cell apoptosis; (3) in long-term cultures, bone marrow stromal cells, but not preB cells, express AhR mRNA and protein as determined by in situ hybridization, RT-PCR, and immunoblotting; (4) freshly isolated unfractionated bone marrow cells, but not purified bone marrow B cells, express AhR protein as assessed by immunohistochemistry; (5) alpha-naphthoflavone, a competitive AhR inhibitor and cytochrome P450 antagonist, completely blocks DMBA-induced preB cell apoptosis in primary bone marrow cultures; and (6) DMBA or benzo[a]pyrene injection in vivo results in bone marrow cell apoptosis consistent with the death of hematopoietic cells clustered around stromal elements. The results implicate programmed cell death as a mechanism underlying DMBA-mediated immunosuppression and suggest that preB cell death is influenced by local interactions with AhR+ bone marrow stromal cells.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1997

Properties of solutions for a chemotaxis system.

We investigate mathematically the system of equations proposed by Chaplain and Stuart, to describe the chemotactic response of endothelial cells under the angiogenesis stimulus. In particular, we characterize the steady state endothelial cell density function, and give conditions on the chemotactic parameter k and cell proliferation parameter b that ensure that migration/ proliferation either does or does not occur in steady state. The time dependent problem is also treated.

Angiogenesis Inducing Agents↗
PubMed1997

Extended primary culture of human hepatocytes in a collagen gel sandwich system.

To develop a strategy for extended primary culture of human hepatocytes, we placed human hepatocytes between two layers of collagen gel, called a "collagen gel sandwich." Maintenance of hepatocellular functions in this system was compared with that of identical hepatocyte preparations cultured on dry-collagen coated dishes or cocultured with rat liver epithelial cells. Human hepatocytes in a collagen gel sandwich (five separate cultures) survived for more than 4 wk, with the longest period of culture being 78 d. They maintained polygonal morphology with bile canaliculuslike structures and high levels of albumin secretion throughout the period of culture. In contrast, hepatocytes on dry-collagen became feature-less, and albumin secretion could not be detected after 14 d of culture. This loss of albumin secretion was partially recovered by overlaying one layer of collagen gel. Ethoxyresorufin O-deethylase activity, associated with cytochrome P450 1A2, was detected basally up to 29 d in collagen gel sandwich culture. These activities were induced four- to eightfold after induction with dibenz(a,h)anthracene. Cocultures also maintained basal activity up to 29 d. However, their inducibility was lower than that of hepatocytes in collagen gel sandwich. No ethoxyresorufin O-deethylase activity was detected in hepatocytes cultured on dry-collagen at 7 d. Thus, the collagen gel sandwich system preserves differentiated morphology and functions of human hepatocytes in primary culture for a prolonged period of time. This system is a promising model for studying human hepatocellular function, including protein synthesis and drug metabolism in vitro.

Adolescent↗
PubMed1997

Balloon versus patch angioplasty as an adjuvant treatment to surgical thrombectomy of hemodialysis grafts.

BACKGROUND: Transluminal balloon angioplasty offers advantages to patch angioplasty. We evaluated the primary patency of thrombosed hemodialysis grafts that had undergone balloon angioplasty versus patch angioplasty as a salvage method. METHODS: We reviewed our experience with 22 consecutive intraoperative balloon angioplasties that were done in a 6-months period. The balloons used were noncompliant high pressure balloons. The balloon results were compared with those of 22 patients who had undergone patch angioplasties by the same surgeons. Age, gender, average time between graft insertion and revision, and number of prior revisions were analyzed. The two groups (patch and balloon) had similar ages (57 versus 58 years, respectively), gender distribution (12 women, 11 men versus 11 women and 11 men), average time of revisions before that particular procedure (15 versus 12 months), and average times of revisions before that procedure. RESULTS: Primary patencies of the patch and balloon group were respectively 86% versus 77% at 1 month, 45% versus 40% at 3 months, and 17% versus 28% at 6 months. There was no statistically significant difference between the two groups. Complications were comparable in both groups. CONCLUSION: Balloon angioplasty offers advantages to patch angioplasty, and we have shown similar patency rates. We recommend balloon angioplasty as a comparable method to salvage dialysis access grafts.

Adult↗
PubMed1997

Endothelial calcium-calmodulin dependent nitric oxide synthase in the in vitro vascular hyporeactivity of portal hypertensive rats.

BACKGROUND/AIMS: Increased nitric oxide production has been implicated in impaired vascular responsiveness to vasoconstrictors in portal hypertension. However, there is no firm evidence concerning the involved nitric oxide synthase isoform. The present study investigated the possible contribution of one nitric oxide synthase isoform, the endothelial constitutive Ca2+-calmodulin dependent, in the overproduction of nitric oxide in portal hypertension. METHODS: Vascular responses to norepinephrine and acetylcholine were evaluated in isolated thoracic aortic rings from normal and portal vein stenosed rats. RESULTS: An impaired concentration-dependent contraction to norepinephrine was observed in intact rings from portal hypertensive rats compared to controls. The hyporeactivity to norepinephrine was reversed after endothelium denudation, the inhibition of nitric oxide synthase with L-NOARG or the inhibition of calmodulin with W-7, but not after pre-incubation with indomethacin. Stimulation of intact rings with norepinephrine after the inhibition of calmodulin with calmidazolium was followed by a decreased vascular response in vessels from normal rats but not in those from portal hypertensive rats. Stimulation of intact rings with norepinephrine in a Ca2+-free medium was followed by a decreased vascular response in vessels from both portal hypertensive and normal rats. No difference in vasoconstrictive responses was observed between the two groups after calmidazolium or in a Ca2+-free medium. Relaxation induced by acetylcholine in norepinephrine-precontracted rings was more marked in rings from portal hypertensive rats than in controls. No differences in the vasodilator responses were observed after relaxations had been inhibited by the removal of the endothelium, pre-incubation with L-NOARG, indomethacin, W-7 or calmidazolium and in a Ca2+-free medium. CONCLUSIONS: This study demonstrates the involvement of the endothelial constitutive Ca2+-calmodulin dependent nitric oxide synthase isoform in the overproduction of nitric oxide in portal hypertension.

Animals↗
PubMed1997

Natriuretic response to the combination of atrial natriuretic peptide and terlipressin in patients with cirrhosis and refractory ascites.

BACKGROUND/AIMS: Refractory ascites, which occurs in certain patients with cirrhosis, is associated with a blunted natriuretic response to exogenous atrial natriuretic peptide (ANP). Since this blunting seems to be related to ANP-induced arterial hypotension, a vasoconstrictor, such as terlipressin (a vasopressin analogue), may restore natriuresis to exogenous ANP. Moreover, since cirrhosis-elicited vasodilation is thought to play a role in sodium retention, a vasoconstriction caused by terlipressin alone may lead to an increase in sodium excretion. This study aimed to evaluate the natriuretic response to either a combination of ANP with terlipressin or terlipressin alone in patients with cirrhosis and refractory ascites. METHODS: Sixteen consecutive patients with cirrhosis and refractory ascites were randomly assigned to receive either a combination of terlipressin (1-2 mg, i.v. bolus) with ANP (35 ng/kg, i.v. bolus followed by 15 ng x kg(-1) x min(-1) for 60 min) (n=8) or terlipressin alone (1-2 mg, i.v. bolus) (n=8). Sodium excretion and urine output, systemic, splanchnic and renal hemodynamics and renal oxygen consumption were measured before and during treatments. RESULTS: Combined therapy did not change arterial pressure but significantly increased urinary sodium excretion and urine output. These effects were associated with a significant increase in glomerular filtration rate and a decrease in renal oxygen consumption. Terlipressin alone significantly increased arterial pressure but did not change urinary sodium excretion or urine output. Moreover, terlipressin did not change either glomerular filtration rate or renal oxygen consumption. CONCLUSIONS: The combination of exogenous ANP with terlipressin, but not terlipressin alone, increases sodium excretion in patients with cirrhosis and refractory ascites.

Adult↗
PubMed1997

Organizational actions of sex hormones on sexual partner preference.

Sexual dimorphism in copulatory behavior results from organizational actions of sex steroids (permanent effects of sex steroids occurring during early development). Reproductive success depends not only on copulatory behavior, but also on mate choice, which is often sexually dimorphic as well. The clearest example is sexual partner preference: the preference of males for female sexual partners and females for males. Are organizational hormone actions responsible for sexual differentiation of sexual partner preference? The zebra finch (Taeniopygia guttata) is a potentially valuable species for addressing this question, because the birds form life-long socially monogamous pair bonds. In one experiment, both early estrogen treatment (injection with estradiol benzoate-EB-for the first 2 weeks posthatch) and unisex housing during juvenile development independently resulted in a preference for females over males in two-choice tests, and only females that experienced both EB treatment and unisex living were more likely than controls to pair with other females in colony tests. In a second experiment, females injected with an estrogen synthesis inhibitor for the first week posthatch preferred to spend time near females instead of males in two-choice tests, unlike control females. These experiments suggest that sexual partner preference may result from organizational hormone actions in this pair-bonding species. Possible neural mechanisms or sites that could underly hormonal organization of sexual partner preference in birds and mammals include the anterior hypothalamic/preoptic area, the corticomedial amygdala, and its avian homologue nucleus taeniae of the archistriatum, the septum, and peripheral sensory processes.

Animals↗
PubMed1997

Implantation of a refillable glucose monitoring-telemetry device.

This study describes the components and short-term in vivo evaluation of an integrated implantable system consisting of an amperometric glucose biosensor, a miniature potentiostat, a FM signal transmitter, and a power supply. The device (dimensions: 5.0 x 7.0 x 1.5 cm) was implanted subcutaneously in healthy mongrel dogs. The biosensor performance was evaluated in vitro prior to implantation using standard solutions simulating the physiological environment. A linear response to glucose concentration was observed throughout the physiological and pathophysiological range (with an upper limit of 25 mM glucose, and a sensitivity of 0.5 microA/mM). The results of short-term subcutaneous implantation of the integrated system demonstrated good agreement between the glucose concentration measured by the biosensor and that obtained using standard glucose determination methods. The delay-time between the tissue glucose level (measured by the biosensor) and the blood glucose level (obtained by standard methodology) was 3-7 min. These results demonstrated the feasibility of data transmission by a telemetry system through the skin of a dog and allowed the commencement of chronic in vivo testing. During the chronic implantation the biosensor was refilled in vivo. A rejuvenation of the sensor's response after refilling was observed suggesting the potential of such sensors for long-term implantation.

Animals↗
PubMed1997

Inactivation of monoamine oxidase B by benzyl 1-(aminomethyl) cyclopropane-1-carboxylate.

Monoamine oxidase (MAO) is a flavoenzyme that catalyzes the oxidation of various biogenic and xenobiotic amines. Benzyl 1-(aminomethyl)cyclopropane-1-carboxylate (1) was designed as a diactivated cyclopropane mechanism-based inactivator of MAO (Silverman, R.B.: Ding, C.Z.; Borrillo, J.L.; Chang, J.T.J. Am. Chem. Soc. 1993, 115, 2982). [1,1-2H2]-1 exhibits a deuterium isotope effect of 4.5 on inactivation, but in D2O the isotope effect is only 2.3. [1-3H]-1 and [1-14C]-1 were synthesized; upon inactivation of MAO, 1.1 and 2.0 equiv of radioactivity, respectively, are incorporated into the enzyme. Tritium as 3H2O, is released during inactivation with [1-3H]-1. The flavin absorption spectrum changes from that of oxidized to that of reduced flavin after inactivation; denaturation of the inactivated enzyme shows a reduced flavin spectrum, suggesting the formation of a modified flavin. Tryptic digestion of the enzyme labeled with [1-3H]-1 or [1-14C]-1, followed by HPLC analysis, monitoring at 310 nm [corrected] (flavin), shows that the radioactivity comigrates with the 310 nm [corrected] absorptions. The metabolites that are generated during inactivation are benzyl 1-formylcyclopropane-1-carboxylate, benzyl alcohol, and 1-formylcyclopropane-1-carboxylic acid; no ring-cleaved products were detected. The partition ratio, as determined from the ratio of nonamines to enzyme, is 110. These results are rationalized in terms of a single-electron transfer mechanism leading to the imine of benzyl 1-formylcyclopropane-1-carboxylate, which alkylates the flavin coenzyme.

Amino Acids↗
PubMed1997

Audio signal feedback light source-guided endotracheal intubation.

OBJECTIVE: Light source-guided endotracheal intubation, whether by lighted stylet or fiber-optic laryngoscopy may potentially be improved by electrical conversion of the detected optical signal to an audio signal. The audio signal thus serves as a feedback guiding signal. METHODS: The optical-to-audio signal conversion is accomplished using a light source, an optical detector and a voltage-to-frequency conversion system. The intensity of the detected optical signal determines the frequency of the audio-signal. Therefore the frequency of the audio signal varies as the light source approaches the optical detector. The light source may be placed in the orotracheal airway and the detector may be placed on cricothyroid membrane or these components may be placed in the opposite orientation. RESULTS: The theory of operation and the construction of a prototype are described. CONCLUSION: This optical-audio signal feedback system may be used to direct the lighted stylet from the oral cavity into the laryngeal-tracheal pathway. This may potentially be a more sensitive technique than the currently used visual intensity detection.

Acoustics↗
PubMed1997

Seroprevalence of CagA-positive strains among Helicobacter pylori-infected, healthy young adults.

Helicobacter pylori is categorized into two phenotypes on the basis of the presence or absence of the CagA protein. CagA protein-positive H. pylori are more closely associated with peptic ulcer disease and cancer. Whether CagA-positive strains are similarly represented among racial or ethnic groups in northern California was investigated. Sera from 152 H. pylori-infected healthy young adults were tested by ELISA for IgG against CagA. CagA antibodies were detected in 79.4% of blacks, 63.8% of Hispanics, and 50% of whites. After adjusting for demographic factors, blacks had significantly more infections with CagA-positive H. pylori than did whites (odds ratio [OR] = 5.0; 95% confidence interval [CI] = 1.6-15.3) or Hispanics (OR = 5.5, 95% CI = 1.9-16.0). Also, there was a higher prevalence of CagA in persons born in developing countries than in persons born in industrialized nations (OR = 3.5, 95% CI = 1.3-9.4). This suggests either a genetic predisposition of racial or ethnic groups to infection with particular H. pylori phenotypes or transmission of H. pylori within relatively segregated population groups.

Adult↗
PubMed1997

Mitomycin-C induced hemolytic uremic syndrome: a case report and literature review.

Hemolytic uremic syndrome spontaneously arises in a few patients with advanced cancer, but it is more commonly related to the use of certain chemotherapeutic agents. Mitomycin-C is, etiologically, the most common causative agent inducing hemolytic uremic syndrome, in a dose dependent manner. We report this syndrome, attributable to mitomycin-C at a cumulative dose of 40 mg/m2, in a gastric cancer patient. A 42-year-old female with stage III gastric cancer underwent radical gastrectomy and was given mitomycin-C at 10 mg/m2 intravenously every four weeks as adjuvant therapy. Hemolytic uremic syndrome was diagnosed three months after the last dose of mitomycin-C administration. The most prominent symptoms included pallor, hypertension and anasarca, with laboratory evidence of microangiopathic hemolytic anemia, azotemia and hyperkalemia. Her disease was progressive, but fortunately stabilized after staphylococcus column A dialysis. Her disease remained in remission for 24 months from the time of diagnosis, and then relapsed in the form of peritoneal carcinomatosis with partial intestinal obstruction.

Adenocarcinoma↗
PubMed1997

GroE assists refolding of recombinant human pro-urokinase.

GroE, one of the molecular chaperones, facilitates correct protein folding both in vitro and in vivo. The refolding of recombinant human pro-urokinase, a protein with a high content of disulfide bonds, was used as a model system to illustrate the mechanism of action of GroE. Aggregation of this protein predominates during its in vitro refolding, as indicated by a strong, concentration-dependent increase in light scattering. The addition of GroE and Mg-ATP significantly increases the yield of the active protein. GroE specifically inhibits the aggregation reaction that competes with correct folding, as shown by a strong decrease in the intensity of light scattering. GroEL rapidly binds to unfolded or partially folded pro-urokinase molecules and thus protects them from the aggregation reaction. Interaction with GroES and ATP hydrolysis are required for the release of the polypeptide chain from GroEL and further acquisition of the completely folded, native conformation.

Adenosine Triphosphate↗