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Biomedical subjects

T H Chiu

Publications and source records attributed to T H Chiu.

At least 145 records · Page 8Linked to original sources
PubMed1979

Differential effects of triton X-100 on benzodiazepine and GABA binding in a frozen-thawed synaptosomal fraction of rat brain.

The effect of Triton X-100 on 3H-GABA and 3H-diazepam binding was measured in a frozen-thawed synaptosomal fraction of rat brain. Specific binding activity (amount bound per mg protein) of both ligands was increased by the treatment. Diazepam binding capacity in the pellet was progressively decreased, while GABA binding was increased, then decreased by increasing Triton X-100. Diazepam binding affinity was unchanged, while GABA binding affinity increased. Triton X-100 appears to preferentially solubilize benzodiazepine binding sites, indicating GABA and benzodiazepine binding sites are on separate macromolecules.

Animals↗
PubMed1979

GABA receptor-mediated modulation of 3H-diazepam binding in rat cortex.

Three membrane preparations of rat cortex were used to examine the effects of GABA, bicuculline and bicucine on specific 3H-diazepam binding. In the crude synaptosomal fraction, GABA had no effect on either the maximal binding capacity (Bmax) or dissociation constant (KD) of 3H-diazepam binding. Bicuculline and bicucine both decreased binding affinity. This was antagonized by adding GABA. In the repeatedly washed membrane preparation, and in the washed, frozen and thawed preparation, GABA increased binding affinity and, at high concentrations, increased Bmax. Increased binding affinity was observed with as little as 10(-8) M GABA in the washed, frozen and thawed preparation. Bicuculline inhibited the effect of GABA on 3H-diazepam binding. It was found that about 3 X 10(-5) M GABA was present in the assay medium containing crude synaptosomal fraction. These results suggest endogenous GABA is present in, and influences the results of 3H-diazepam binding assays. Furthermore, it appears that GABA and bicuculline affect 3H-diazepam binding through their binding to the specific GABA binding site.

Animals↗
PubMed1979

Benzodiazepine binding after in vivo elevation of GABA.

[3H]Diazepam binding was measured in rat cortical membranes. Acute and chronic amino-oxyacetic acid (AOAA) pretreatment greatly increased GABA levels, but did not alter diazepam binding. The GABA normally present was sufficient to maximally stimulate diazepam binding. In in vivo binding studies, acute and chronic AOAA treatment increased the amount of [3H]diazepam in the brain at the time of sacrifice, thus increasing both specific and nonspecific binding and leaving unchanged the fraction of drug specifically bound. Fluctuation of brain GABA may not affect benzodiazepine binding unless the normal concentration is greatly depressed.

Aminooxyacetic Acid↗
PubMed1979

Biosynthesis of glycosylated glycerolphosphate polymers in Streptococcus sanguis.

Two types of glycosylated glycerolphosphates were synthesized when a particulate enzyme prepared from Streptococcus sanguis was incubated with [3H]-phosphatidylglycerol and uridine diphosphate-[14C]glucose in the presence of MgCl2. The first type was extractable with saline and contained no fatty acid. The second type was pellet bound and could be extracted with 0.1% sodium dodecyl sulfate. Both types of polymers were purified and partially characterized. The first type of polymer was fractionated into five polymers, peaks 2a, 2b, 2c, 3a, and 3b. All except peak 2a, which contained only [3H]glycerol, contained both [3H]glycerol and [14C]glucose. [3H]NaBH4 reduction of acid hydrolysates of the polymers revealed that all of the polymers contained glucose as the major sugar componenta nd xylose as the minor sugar component. The second type of polymer was fractionated into three polymers, P-1, P-2, and P-3. All contained [3H]-glycerol, [14C]glucose, and fatty acids. P-1 appeared to be pure, whereas P-2 and P-3 contained two polymers each, as judged from sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Glucose↗
PubMed1979

Re-evaluation of the relationship between the positive inotropic effect of ouabain and its inhibitory effect on (Na+ + K+)-dependent adenosine triphosphatase in rabbit and dog hearts.

Previous studies have shown that in the ouabain-exposed rabbit heart, although positive inotropy and inhibition of (Na+ + K+)-dependent adenosine triphosphatase are induced concomitantly, the extent of inhibition of the enzyme remains constant when positive inotropy is washed out; and in the dog heart, if positive inotropy without arrhythmias is induced by ouabain, inhibition of the enzyme is not detected. The purpose of this work was the re-evaluation of these previous findings. Rapid recovery of the enzyme from small tissue samples was achieved by homogenization in 1 M KCl and centrifugation. When the enzyme was prepared by this method from ouabain-exposed rabbit and dog hearts, ouabain remained bound to the enzyme. The extent of inhibition of the enzyme was measured by the fluorimetric assay of K+-dependent 3-O-methylfluorescein phosphatase before and after removal of bound ouabain. Correlation between the extent of inhibition of this activity and that of (Na+ + K+)-dependent adenosine triphosphatase activity was established. Utilizing these refined methods, the following results were obtained. In the rabbit heart, positive inotropy and enzyme inhibition occurred concomitantly. Washout of the effect resulted in partial reactivation of the enzyme. In the dog heart, the previous findings were confirmed. The results are not inconsistent with the hypothesis that enzyme inhibition is the cause of the positive inotropic effects. They do suggest, however, the need for further testing of the hypothesis.

Animals↗
PubMed1978

Chronic effects of 6-hydroxydopamine and reserpine on myocardial adenylate cyclase.

The effects of chronic administration of 6-hydroxydopamine or reserpine on catecholamine-sensitive adenylate cyclase from rat hearts were studied. Not only basal adenylate cyclase activity, but stimulation of the enzyme by norepinephrine, isoproterenol, NaF, guanylyl-imidodiphosphate, or combination of isoproterenol and guanylyl-imidodiphosphate, was significantly increased in the treated than in the control hearts. It is inferred that supersensitivity of myocardial adenylate cyclase following chronic treatment with reserpine or 6-hydroxydopamine may result from an increase in the catalytic activity of the enzyme.

Adenylyl Cyclases↗
PubMed1978

Biosynthesis of oligosaccharide-lipid in Streptococcus sanguis.

An oligosaccharide-lipid containing N-acetyl d-glucosamine (GlcNAc), l-rhamnose, and d-glucose was synthesized when the particulate enzyme from Streptococcus sanguis was incubated with UDP-GlcNAc, TDP-rhamnose, and UDP-glucose. The incorporation of d-glucose into the lipid was dependent on the preincorporation of l-rhamnose, which in turn was dependent on that of GlcNAc. This indicates that the order of sugar incorporation is GlcNAc, l-rhamnose, and d-glucose. The synthesis of GlcNAc-lipid was stimulated twofold by ATP and was inhibited strongly by UDP and slightly by UMP, CDP, and TDP, but not by all other nucleoside diphosphates and nucleoside monophosphates tested. A [gamma-(32)P]ATP labeling experiment indicated that some acceptor lipid was present in nonphosphorylated form. The acid and alkaline stabilities of the GlcNAc-lipid were similar to those of glycosyl undecaprenylphosphate, and the thin-layer chromatographic mobility of the lipid was slightly faster than that of the mannosylphosphorylundecaprenol. The molar ratio of phosphate to GlcNAc in purified GlcNAc-lipid was found to be 0.96:1. These results suggested that the GlcNAc was attached to the lipid moiety, presumably undecaprenol, by phosphodiester bonds. The incorporation of l-rhamnose into the lipid was inhibited by UDP and UMP, respectively, in a manner similar to the incorporation of GlcNAc. This suggested that the oligosaccharide was also linked to the lipid moiety by phosphodiester bonds.

Acetylglucosamine↗
PubMed1978

Effects of small amounts of pentadecan-2-one on the growth of Clostridium butyricum.

Primary alcohols occur as trace lipids and are the only long-chain alcohol species present in Clostridium butyricum. Secondary alcohols do not occur physiologically in this microorganism. Exposure of these cells to the methyl ketone, pentadecan-2-one, results in a marked decrease in the primary alcohol content with the secondary alcohol, pentadadecan-2-ol, becoming the major alcohol present. This change in lipid composition is associated with a significant decrease in growth rate that is proportional to the log of the pentadecan 2-one concentration of the incubation medium. When these cells are incubated with pentadecan-2-ol alone, growth is unaffected. Simultaneous exposure of the bacteria to pentadecan-2-one and a mixture of primary alcohols results in a partial relief of the growth inhibition observed with the ketone alone. These observations indicate that pentadecan-2-one inhibits the formation of primary alcohols that are important for normal growth of this bacterium.

Alcohols↗
PubMed1977

Effects of polymer surface molecular structure and force-field characteristics on blood interfacial phenomena.

To quantify the effects of major surface structural factors influencing interfacial reactions induced by polymers in native blood, model surfaces of solvent-cast films of two analogous poly(ether urethanes) and three homologous polyamides (nylon 4, 6/6, and 12) were exposed ex vivo to canine blood under the well-defined hemodynamic conditions of the Stagnation Point Flow Experiment. The selected surfaces allow for incremental changes in properties and were characterized by their "Composite Surface Free ENergy Function," gamma'S, which describes the surface force field as the sum of the mean dispersion (gammaSd) and polar (gammaSp) contributions and is computed from wettability spectra obtained with ultrapure diagnostic liquids. Blood interfacial effects were measured by the shear-limited diameter of the white cell circle formed around the stagnation point, the flow parameter at which symmetric aggregation occurred, and the surface-number density of platelets, [P s], remaining adherent under fixed conditions. At identical flows, within each group of polymers, both the WBC-circle diameter and [P s] scale with gamma Sp/gamma'S, implying that 1) only the magnitude but not the interaction mechanism varies as a function of incremental structural and surface changes, 2) the primary determinant of surface-induced effects is the polar force contribution, and 3) the magnitude of gamma'S is secondary if gammaSd/gamma'S is sufficiently great.

Adsorption↗
PubMed1976

Thermodynamics of native protein/foreign surface interactions. IV. Calorimetric and microelectrophoretic study of human fibrinogen sorption onto glass and LTI-carbon.

1. According to a working hypothesis put forward in the previous papers of this series2-4, the initial phases of native blood/foreign surface interactions have been considered within the framework of a physicochemical model of contact activation at the molecular level. The salient features of this hypothesis are: a) the arrival and adsorption of native plasma proteins on a contact surface overwhelmingly precedes that of the cellular blood components; b) the interaction energy that arises between a particular foreign surface and native plasma proteins settling on it, is a characteristic quantity depending upon the effective surface molecular structure as well as the nature of the proteins; c) the "intensity" of native protein/foreign surface interactions can be treated in terms of thermodynamic quantities since these energy terms are independent of the type of forces acting between protein and surface; and d) depending upon the degree to which the adsorption of a native protein is thermodynamically favored by enthalpy and/or entropy factors, the interaction energy can be utilized to induce conformational changes of varying degree in the sorbed protein. 2. Using glass and low temperature isotropic (LTI) carbon adsorbents, i.e., a known procoagulant and a relevant biomaterial, respectively, the adsorption properties and the potential surface-induced conformational changes of high-purity native human fibrinogen (clottability greater than or equal to 92%) were studied, at 25 degrees C, by 3 independent methods. In all of the experiments performed, a) both adsorbents were employed in the form of particles less than or equal to 1.0 mu representing specific surface areas of 9.85 M2/Gm and 27.7 (nominal) M2/Gm for the glass and LTI-carbon powders, respectively, and b) the fibrinogen was absorbed from a standaridized buffer (pH = 7.2, ionic strength 0.05) using the same fixed surface area/protein solution volume ratio with a given adsorbent. 3. The 25 degrees C adsorption isotherms of fibrinogen obtained for both the glass and LTI-carbon powder adsorbents are not amenable to Langmuir type analysis but indicate multilayer sorption with a possible change in binding mechanism after the completion of the first sorbed monolayer. The adsorptivities attained at first monolayer coverage were slightly greater on glass (approximately 0.76 mug/cm2) than on LTI-carbon (approximately 0.52 mug/cm2). 4. Using a custom-built, thermistorized, isothermal-jacketed microcalorimeter routinely capable of resolving temperature changes of 0.00001 degrees C in 100 ml of aqueous sample volume, the "intensity" of interaction between fibrinogen and each of the microparticulate adsorbents was studied by the direct measurement of the net overall enthalpy changes, hI(SLP)25 arising as a result of protein adsorption. From these values, the net heat of protein sorption has been determined...

Adsorption↗
PubMed1976

The intravascular magnetic suspension of a test device for in vivo hemocompatibility evaluation of biomaterials.

To advance hemocompatibility evaluation techniques, a new in vivo method has been developed for the dynamic testing of candidate biomaterials in suitably-sized experimental animals. One of the salient features this method is that the material to be evaluated constitutes the blood contact surface of a slender body of revolution which is coaxially suspended in a large canine vessel by electromagnetic forces only. The insertion site of the specimen is distal and downstream to the test region, reducing the influence of thrombotic tissue substances. These experimental conditions also insure that the only chronically exposed foreign surface is that of the test material, whose interactions with blood components are not affected by contact with the vessel intima. As demonstrated in simulated Circulation Model experiments, macroscopic thromboembolic phenomena induced by the test material can be continuously monitored. Preliminary in vivo trials have verified the validity of the underlying principles; the feasibility of the required surgical techniques, and the adequate performance of the suspension system.

Animals↗