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Biomedical subjects

X Qi

Publications and source records attributed to X Qi.

At least 73 records · Page 4Linked to original sources
PubMed1996

Vascular-derived myocardial contractile factor: positive myocardial inotropic substance released from medial layer of the canine aorta.

Interactions between the various cell types that make up the cardiovascular system are known to play an important role in maintaining homeostasis. One area about smooth muscle cells that has received little attention, despite the production of a wide variety of mediators by smooth muscle cells, is their effect on myocardial function. In this study, the myocardial contractile effects of four different types of dog aortic strips on rabbit papillary muscles were evaluated. Of these, medial vascular smooth muscle strips most consistently (65% of the time) produced a "vascular-derived contractile factor" (VDCF), which caused a 15% increase in isometric twitch tension and a 24% increase in isotonic twitch shortening with no change in twitch configuration. Endovascular strips with or without intact endothelium and complete aortic rings had less consistent effects. Vascular-derived contractile factor was stable after freezing at -80 degrees C, its activity was not modified by a broad spectrum peptidase, but it was heat-labile. The angiotensin II blocker, losartan, did not modify its effects. However, incubation with indomethacin did reduce, but did not eliminate, the contractile effects of vascular strips. The addition of alpha 1- and beta-blockers did not further modify the effects of VDCF. Endocardial endothelial removal increased the effects of VDCF. No correlation existed between endothelin levels and the contractile effects of vascular strips. It is concluded that VDCF is produced by the medial layer of large vessels but its exact cellular origin is uncertain. These findings expand the ever-increasing understanding of the inter-relationship between the structures that make up the cardiovascular system, and open the door to new studies evaluating the inter-relationship of vessels and myocardium.

Animals↗
PubMed1996

An acidic amino acid-specific protease from germinating soybeans.

The degradation of the beta-conglycinin protein reserves in soybean seeds during germination and early growth begins with the proteolysis of its alpha and alpha' subunits by an enzyme called Protease C1. In the pathway, a number of proteolytic intermediates are produced and subsequently degraded. Determination of the N-terminal sequences of these intermediates provides insight regarding the requirements of the cleavage sites. The N-terminal sequence of three such proteolytic intermediates has been determined. The sequence has been located in the published sequences of the beta-conglycinin subunits. Comparing these cleavage sites, plus those of two others previously delineated, shows that the P1' and P4' positions always bear either a Glu or an Asp residue while the P1 position always bears either a Glu or a Gln residue. In addition, other sites from P3 to P7' are also rich in either Glu or Asp, and the whole region is predicted to be in a alpha-helix. Consistent with the observation, synthetic poly-L-Glu inhibits the Protease C1-catalysed degradation of the alpha and alpha' subunits of beta-conglycinin. Poly-L-Glu (av. M(r) = 1000) at 12.5 mM was more effective at inhibiting the reaction than poly-L-Glu (av. M(r) = 600) or poly-L-Glu (av. M(r) = 14,300) at the same concentration. Comparing large synthetic polypeptides at 12.5mM, inhibition by poly-L-Asp (av. M(r) = 15,000) is as effective as poly-L-Glu (av. M(r) = 14,300), while poly-L-Ser (av. M(r) = 15,000) had no effect at all. Poly-D-Glu (av. M(r) = 15,000) is a better inhibitor than poly-L-Glu of the same size. A serine protease of similar molecular weight as Protease C1 and also capable of catalysing the proteolysis of the alpha and alpha' subunits of beta-conglycinin to generate proteolytic intermediates of the same size has been found in mung bean.

Amino Acid Sequence↗
PubMed1996

Basal phosphorylation of the PEST domain in the I(kappa)B(beta) regulates its functional interaction with the c-rel proto-oncogene product.

The product of the c-rel proto-oncogene (c-Rel) belongs to the NF-kappaB/Rel family of polypeptides and has been implicated in the transcriptional control of cell proliferation and immune function. In human T lymphocytes, c-Rel is sequestered in the cytoplasmic compartment by constitutively phosphorylated inhibitors, including I(kappa)B(alpha) and I(kappa)B(beta). Studies with bacterially expressed forms of these inhibitory proteins revealed that unphosphorylated I(kappa)B(alpha) but not I(kappa)B(beta) assembles with c-Rel and inhibits its DNA binding activity. Furthermore, latent I(kappa)B(beta)-c-Rel complexes derived from mammalian cells were sensitive to phosphatase treatment, whereas I(kappa)B(alpha)-c-Rel complexes were resistant. We have identified a constitutive protein kinase in unstimulated T cells that associates with and phosphorylates I(kappa)B(beta) in vitro. The substrate specificity, electrophoretic mobility, and antigenic properties of this I(kappa)B(beta)-associated kinase (BAK) suggest identity with casein kinase II (CKII), an enzyme known to mediate basal phosphorylation of I(kappa)B(alpha). Phosphorylation of recombinant I(kappa)B(beta) by either BAK or CKII restored the capacity of this inhibitor to antagonize the DNA binding activity of c-Rel. Peptide mapping and mutational analyses localized the bulk of the basal phosphorylation sites in I(kappa)B(beta) to the C-terminal PEST domain, which contains two potential acceptors for CKII-mediated phosphoryl group transfer (Ser-313 and Ser-315). Point mutations introduced into the full-length inhibitor at Ser-313 and Ser-315 led to a significant reduction in the phosphorylation of I(kappa)B(beta) and severely impaired its c-Rel inhibitory function in vivo. Taken together, these findings strongly suggest that basal phosphorylation of the PEST domain of I(kappa)B(beta) at consensus CKII sites is required for the efficient formation of latent I(kappa)B(beta)-c-Rel complexes.

Amino Acid Sequence↗
PubMed1996

Growth hormone upregulates gastrin and peptide YY gene expression.

The purpose of these studies was to examine the effects of excess growth hormone (GH) on gastrin and peptide YY (PYY) gene expression. Transgenic mice with the bovine GH gene linked to a mouse metallothionein I promoter were used as a model of chronic GH excess. Antral gastrin mRNA and peptide levels were elevated significantly (P < 0.05) in GH transgenic mice compared with wild type littermates. Ileal PYY mRNA and ileal and colonic PYY levels were significantly elevated in GH transgenic mice compared with wild type littermates. The elevations in gastrin and PYY gene expression in GH transgenic mice were independent of food intake. Serum concentrations of gastrin and PYY were also elevated in GH transgenic mice. Immunohistochemical analysis showed that the density of PYY-containing cells in the colon of GH transgenic mice and wild type littermates did not differ. In addition, the mRNA and protein levels of chromogranin A, a marker of endocrine cells, were not increased in the colon of GH transgenic mice. Together, these data indicate that GH, insulin-like growth factor I, or both can upregulate gastrointestinal gastrin and PYY gene expression directly.

Animals↗
PubMed1996

Beta-adrenergic responsiveness of papillary muscles in the rat postinfarction model.

Rats in which ligation of the left anterior descending (LAD) coronary artery did not result in an infarct visible to the naked eye have generally been called sham-operated controls and have been used to evaluate changes in the characteristics of the remaining viable myocardium of rats where myocardial infarction was present. Whether these sham-operated rats are equivalent to normal controls or whether they have been altered by the surgery is unknown. The purpose of this study was to evaluate potential differences in papillary muscle mechanical characteristics and responsiveness to beta-adrenergic stimulation in control, open-chest, sham-operated (aborted infarct), and infarct rats 4 weeks after surgery. Absence of significant myocardial damage was verified by morphologic examination in sham-operated hearts: myocardial infarction scar was 1.5 +/- 0.6% (mean +/- SE) of circumference, no infarct being transmural. Basal contractile indices were decreased in papillary muscles in infarct rats compared with the three other groups. The response in contractile indices of infarct muscles to isoproterenol was also less compared with the other three groups. However, although basal contractility was the same in muscles from sham-operated, open-chest, and controls, the responsiveness of sham-operated muscles to isoproterenol was less: change in total tension of 2.9 +/- 1.2% vs. 9.5 +/- 2.7% for controls and 9.3 +/- 2.4% for open-chest (p < 0.05). Percent change in maximum rate of tension development (+dT/dt) was also less in muscles from sham-operated versus control muscles (21 +/- 2 vs. 33 +/- 6%; p < 0.05). Twitch configuration changed similarly with isoproterenol in all four groups. Thus, although contractility is unaffected by sham operation, beta-adrenergic responsiveness of tension-generating indices is modified.

Adrenergic beta-Agonists↗
PubMed1996

[A study on red blood cell immune function in patients with Guillain-Barré syndrome and multiple sclerosis].

In order to understand whether there is red blood cell (RBC) immune dysfunction and the relationship between RBC immune abnormality and clinical state in patients with multiple sclerosis (MS) and Guillain-Barré syndrome (GBS), RBC immune function and circulation immune complex (CIC) level were evaluated in patient with these two diseases by using RBC immune adhesion test. It was found that the rate of formation of red blood cell-C3b receptor-yeast rosette was significantly lower in patients with these two diseases before and after treatment than that in a control group (P < 0.01). The rate of formation of red blood cell-immune complex-yeast rosette and the CIC level in GBS group were notably higher than that in the control group (P < 0.05). Moreover, we observed that the immune functions in patients with severe GBS and active MS were different from those in patients with mild GBS and stable MS and the change of each immune index in GBS and MS patients was related with the degree of recovery and the clinical state. These results suggested that decreased capability of RBC immune adhesion in patients with GBC and MS may be one of factors causing these diseases.

Adolescent↗
PubMed1995

Zero frequency masking and a model of contrast sensitivity.

Stimulating the visual system tends to desensitize it to certain stimulus properties. Such desensitization is usually called adaptation or masking, but the distinction between the two is unclear. Nonspecific desensitization by light is usually regarded as adaptation, whereas pattern-specific desensitization is typically considered masking. Here we unify the treatment of such desensitizing phenomena by handling both in the spatial frequency domain. The amount of adapting light in a stimulus is represented in the spatial frequency domain by the component at zero frequency. To determine whether such adapting light acts like other components in the spatial frequency domain, we compared the effect of masking by the zero frequency component with the effects of masking by components at other frequencies. We show that the zero frequency component acts like other masking components, decreasing sensitivity to nearby test frequencies and thereby producing the insensitivity to low spatial frequencies that gives the contrast sensitivity curve its band-pass shape at high light levels. Treating light adaptation as masking by the zero frequency component leads to a general model that describes visual sensitivity to test gratings of varying spatial frequency at varying mean luminance, in the presence (or absence) of masking gratings of varying spatial frequency. Individual components of the model provide insight into visual processing at the system level.

Adaptation, Ocular↗
PubMed1995

Plasma membrane intrinsic proteins of Beta vulgaris L.

The plasma membrane (PM) of higher plants contains numerous proteins; however, due to their low abundance, only a few have been identified and characterized by direct biochemical approaches. The major intrinsic protein (MIP) family is a class of highly hydrophobic integral membrane proteins thought to function as channels that facilitate the passage of water, small solutes, and possibly other moieties through the membrane. A family of PM intrinsic proteins was purified and characterized from PM vesicles derived from storage tissue of Beta vulgaris L. using the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate. This PM intrinsic protein-enriched fraction also contains high levels of UDP-glucose:(1,3)-beta-glucan (callose) synthase activity. Dithiothreitol is required to visualize the monomeric species of these highly hydrophobic integral membrane proteins. Sequence analysis of tryptic fragments derived from polypeptides of 31 and 27 kD revealed significant homologies to plant MIPs identified from cloned sequences. These MIPs include clone 7a from pea and RD28 from Arabidopsis, both of which are water-stress proteins, a tomato ripening-associated membrane protein, and PIP 2b, a PM-bound water channel protein from Arabidopsis. MIPs, therefore, represent abundantly occurring components of PMs derived from beet storage tissue.

Amino Acid Sequence↗
PubMed1995

Solubilization and partial characterization of extensin fragments from cell walls of cotton suspension cultures. Evidence for a covalent cross-link between extensin and pectin.

Extensin, a major hydroxyproline (Hyp)-rich glycoprotein in walls of cultured cells of dicotyledonous plants, is very difficult to solubilize. To learn about the nature of the insolubilization, we have tested the ability of a variety of selective hydrolytic methods, and combinations of them, to liberate extensin or fragments of extensin from suspension-culture cell walls. After the complete deglycosylation of cotton (Gossypium hirsutum L.) walls, trypsinization solubilized 80% of the Hyp. The sequences of three abundant peptides were: (a) serine-Hyp-Hyp-Hyp-Hyp-Hyp-Hyp-serine-Hyp-Hyp-lysine, (b) serine-Hyp-Hyp-Hyp-Hyp-valine-lysine, and (c) serine-Hyp-Hyp-serine-alanine-Hyp-lysine. After a sequential treatment of walls with endopolygalacturonase, cellulase, -73 degrees C anhydrous hydrogen fluoride solvolysis, and ammonium bicarbonate extraction, only sugars indicative of rhamnogalacturonan I and protein remained insoluble. Trypsin treatment of this residue liberated 50% of the Hyp. A significant proportion of rhamnogalacturonan-associated sugars co-solubilized and co-purified along with the extensin fragments following the trypsinization. By sodium dodecyl sulfate gel electrophoresis and gel filtration, the glycopeptides fell into two classes. One class contained distinctly sized molecules with relative molecular weights in the range of 4,000 to 24,000. The other class did not enter the resolving gel and was hetero-disperse. After complete deglycosylation by a 0 degrees C anhydrous hydrogen fluoride treatment, the first class was little affected in its electrophoretic mobility, whereas the larger heterogeneous material mostly entered the separating gel. After further trypsinization of the deglycosylated peptides and analysis by capillary zone electrophoresis, the peptides in both size classes were shown to contain the sequences described above. From our observations we suggest that cotton extensin becomes insolubilized into cell walls in part by pectin-protein cross-links in addition to the protein-protein (or protein-phenolic-protein) cross-links that have been repeatedly suggested.

Amino Acid Sequence↗
PubMed1995

Coupling of a signal response domain in I kappa B alpha to multiple pathways for NF-kappa B activation.

The eukaryotic transcription factor NF-kappa B plays a central role in the induced expression of human immunodeficiency virus type 1 and in many aspects of the genetic program mediating normal T-cell activation and growth. The nuclear activity of NF-kappa B is tightly regulated from the cytoplasmic compartment by an inhibitory subunit called I kappa B alpha. This cytoplasmic inhibitor is rapidly phosphorylated and degraded in response to a diverse set of NF-kappa B-inducing agents, including T-cell mitogens, proinflammatory cytokines, and viral transactivators such as the Tax protein of human T-cell leukemia virus type 1. To explore these I kappa B alpha-dependent mechanisms for NF-kappa B induction, we identified novel mutants of I kappa B alpha that uncouple its inhibitory and signal-transducing functions in human T lymphocytes. Specifically, removal of the N-terminal 36 amino acids of I kappa B alpha failed to disrupt its ability to form latent complexes with NF-kappa B in the cytoplasm. However, this deletion mutation prevented the induced phosphorylation, degradative loss, and functional release of I kappa B alpha from NF-kappa B in Tax-expressing cells. Alanine substitutions introduced at two serine residues positioned within this N-terminal regulatory region of I kappa B alpha also yielded constitutive repressors that escaped from Tax-induced turnover and that potently inhibited immune activation pathways for NF-kappa B induction, including those initiated from antigen and cytokine receptors. In contrast, introduction of a phosphoserine mimetic at these sites rectified this functional defect, a finding consistent with a causal linkage between the phosphorylation status and proteolytic stability of this cytoplasmic inhibitor. Together, these in vivo studies define a critical signal response domain in I kappa B alpha that coordinately controls the biologic activities of I kappa B alpha and NF-kappa B in response to viral and immune stimuli.

Base Sequence↗
PubMed1994

Functional human saposins expressed in Escherichia coli. Evidence for binding and activation properties of saposins C with acid beta-glucosidase.

Small (80-amino acid) glycoproteins or saposins are important for the in vivo function of several lysosomal hydrolases. Four saposins, A, B, C, and D, are encoded by a single locus termed prosaposin. Saposins C and A are thought to function in vivo as activators of acid beta-glucosidase. The physiologic role of saposin C has been confirmed, whereas that of saposin A role has not. To investigate the effects of saposins C and A on acid beta-glucosidase activity, the coding sequence for the individual saposins was expressed in Escherichia coli and the recombinant proteins purified to homogeneity. Recombinant and natural saposins A and C activated acid beta-glucosidase similarly only in micromolar amounts. Saposin C had specific activation of acid beta-glucosidase activity at < 200 nM. A second phase of activation was achieved at > 1 microM. In comparison, saposin A consistently activated acid beta-glucosidase only at > 1 microM. Two mutant saposins C (Cys382-->Phe and Cys382--Gly) were created and shown to compete with saposin C for a site on acid beta-glucosidase. The mutant saposins did not activate the enzyme. Recombinant saposin A (< 200 nM) competed with saposin C for a site on the enzyme but without activating effects. These studies show that saposin A is not an in vitro activator of acid beta-glucosidase at physiologic concentrations, although binding occurs without activating acid beta-glucosidase. The studies with mutant saposins C indicate that the binding and activation effects of saposins C are distinct events. These results indicate that the saposin C-induced conformational change in the enzyme occurs via highly specific, probably multivalent, interactions between acid beta-glucosidase and saposin C.

Amino Acid Sequence↗
PubMed1994

Inverse correlation between expression of inducible nitric oxide synthase activity and production of metastasis in K-1735 murine melanoma cells.

The purpose of these studies was to determine whether the induction of NO synthase activity in murine K-1735 melanoma cells correlated with their metastatic potential. Nonmetastatic, metastatic, and somatic cell hybrids (produced by fusion of nonmetastatic and metastatic cells) were injected i.v. into syngeneic C3H/HeN mice. Metastatic cells survived to produce experimental lung metastases, whereas nonmetastatic cells did not. The various clones and somatic cell hybrids were incubated in vitro with combinations of tumor necrosis factor, interleukin 1, gamma-interferon, and lipopolysaccharide. Nonmetastatic cells exhibited high levels of inducible NO synthase activity and NO, whereas metastatic cells did not. Both the cytotoxic effects of the cytokines and NO production were inhibited by the addition of NG-monomethyl-L-arginine, a specific inhibitor of NO synthase. These data demonstrate an inverse correlation between production of endogenous NO and the ability of K-1735 cells to survive in syngeneic mice to produce lung metastases.

Amino Acid Oxidoreductases↗
PubMed1994

Characterization of a soybean beta-conglycinin-degrading protease cleavage site.

Protease C1, an enzyme from soybean (Glycine max [L.] Merrill cv Amsoy 71) seedling cotyledons, was previously determined to be the enzyme responsible for the initial degradation of the alpha' and alpha subunits, but not the beta subunit, of beta-conglycinin storage protein. The sizes of the proteolytic products generated by the action of protease C1 suggest that the cleavage sites on the alpha' and alpha subunits of beta-conglycinin may be located in their N-terminal domain, which is not found in the beta subunit of beta-conglycinin. To check this hypothesis, storage proteins from other plant species that are homologous to either the alpha'/alpha or the beta subunit of beta-conglycinin were tested as substrates. As expected, the convicilin from pea (Pisum sativum), a protein homologous to the alpha' and alpha subunits of beta-conglycinin, was digested by protease C1. The vicilins from pea as well as vicilins from adzuki bean (Vigna angularis), garden bean (Phaseolus vulgaris), black-eyed pea (Vigna unguiculata), and mung bean (Vigna radiata), storage proteins that are homologous to the beta subunit of soybean beta-conglycinin, were not degraded by protease C1. Degradation of soybean beta-conglycinin involves a sequential attack of the alpha subunit at multiple sites, culminating in the formation of a stable intermediate of 53.5 kD and a final product of 48.0 kD. The cleavage sites resulting in this formation of the intermediates and final product were determined by N-terminal analysis. These were compared to the known amino acid sequences of the three beta-conglycinin subunits. Results showed these two polypeptides to be generated by proteolysis of the alpha subunit at regions bearing long strings of acidic amino acid residues.

Amino Acid Sequence↗
PubMed1994

Conjugated deferoxamine reduces blood-brain barrier disruption in experimental optic neuritis.

The purpose of this paper was to investigate the role of deferoxamine (DFO) scavenging of hydroxyl radical (.OH) on disruption of the blood-brain barrier (BBB) and demyelination in experimental optic neuritis. Eighteen strain-13 guinea pigs were sensitized for experimental allergic encephalomyelitis. Nine animals received 100 mg/kg of hydroxyethyl starch-conjugated (HES) DFO by daily intraperitoneal injection commencing the day of antigenic sensitization. Nine paired litter mates received daily IP injections of HES. Serial fat-suppressed magnetic resonance imaging of the optic nerves was obtained with a T2 weighting (T2w) to evaluate demyelination and after intravascular administration of Gd-DTPA to evaluate BBB disruption. The intensity of Gd-DTPA enhancement and T2w signal of the optic nerves was quantitated 3, 7, 10 and 14 days after antigenic sensitization. Animals were then sacrificed and the optic nerves processed for light and transmission electron microscopy with ultracytochemical localization of endogenous hydrogen peroxide (H2O2) and immunogold colocalization of extravasated serum albumin. The area of the optic nerve head, intensity of toluidine blue staining, and the cellular infiltrate were digitized and quantitated. Administration of HES-DFO significantly reduced the intensity of Gd-DTPA enhancement in the optic nerves of HES-DFO-treated animals compared to paired control HES animals (p = 0.0236), with the mean difference between control and treated animals of 19.39. The difference in T2w signal was not significant (p = 0.39), with a mean difference between control and treated animals of -5.51. The intensity of toluidine blue staining of optic nerve specimens was slightly less with HES-DFO compared to untreated animals (mean pair difference 2.48), and the inflammatory infiltrate was reduced with HES-DFO compared to untreated animals (mean pair difference = 61.57); these differences were not statistically significant. In the optic nerve specimens of both groups cerium perhydroxide-derived H2O2 reaction product was evident in a predominantly perivascular and perineural distribution. Immunogold-labeled serum albumin showed extravasation at foci of perivascular inflammation in both the presence and absence of H2O2-derived reaction product. Conjugated DFO reduces disruption of the BBB, as measured by Gd-DTPA enhancement, suggesting the .OH radical generated from perivascular H2O2 may play a role in alterations of vascular permeability in experimental optic neuritis.

Animals↗
PubMed1994

Pericardiocentesis and drainage by a silicon rubber line without echocardiographic guidance. Experience in 55 consecutive patients.

Pericardiocentesis and drainage with a silicon rubber line were performed safely in 55 patients via the subxiphoid (80 times) or apical (1 time) approach at the bedside without echocardiographic guidance. The subxiphoid approach, which is close to the posterior of the sternum or the costal cartilage with a small acute-angle (15-30 degrees) to the parietal pericardium in front of the right ventricle, can avoid injuring the heart, liver and lungs. A line with sideholes near the distal end, which provides convenient drainage and has better histocompatibility, can be kept in place for a long period of time (1-82 days). It was also convenient to inject air, drugs or fluid through the line. There were no procedure-related serious complications or deaths. Emergency drainage with the Seldinger technique, especially for small to moderate effusions, is safe and simple.

Catheters, Indwelling↗
PubMed1993

Two-dimensional high-performance liquid chromatographic method for assaying S-adenosyl-L-methionine and its related metabolites in tissues.

S-Adenosyl-L-methionine (SAM) is a methyl-donor compound which is actively involved in a variety of biochemical reactions. An assay has been developed permitting the quantitative measurement of SAM and its related metabolites (S-adenosylhomocysteine, decarboxylated SAM, methylthioadenosine, adenosine and adenine) in liver and cell cultures. As gradient reversed-phase chromatographic or cation-exchange chromatographic methods often resulted in overlapping peaks, a two-dimensional high-performance liquid chromatographic (HPLC) procedure was developed involving gradient reversed-phase chromatographic separation followed by ion-exchange chromatography. After precipitating large molecules in the sample by perchloric acid, gel permeation was carried out on a Sephadex G 25 column to separate small water-soluble metabolites from proteins and membrane fragments. The freeze-dried sample was injected onto an ODS column and a 0-10% acetonitrile gradient in 10 mM ammonium formate buffer (pH 2.9) (20 min, linear) was applied. The relevant fractions were collected and injected onto a cation-exchange column (Partisil SCX, 10 microns, 250 mm x 4.6 mm I.D.). Elution and quantification were carried out using ammonium formate buffers of various concentration (15-400 mM), pH 2.9. The detector response (254 nm) as a function of concentration was linear over the concentration range 30-500 pmol. The detection limits of the compounds after the two-dimensional chromatographic procedure ranged from 10 to 60 pmol and the recovery was higher than 70%. The reproducibility of the results obtained from given samples was within 9-22% for rat liver and 6-24% for mast cells.

Animals↗