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Biomedical subjects

T Kwan

Publications and source records attributed to T Kwan.

At least 73 records · Page 4Linked to original sources
PubMed1985

Spin label study of the effect of ticlopidine on platelets.

The effect of ticlopidine on platelet membrane fluidity was investigated using a spin label technique. Ticlopidine, when orally administered to rats, increased both the order parameter and the motion parameter, indicating a decrease in the membrane fluidity of platelets. On the other hand, the order parameter and the motion parameter decreased markedly when the platelets were aggregated by thrombin. Ticlopidine inhibited the thrombin-induced aggregation of platelets and caused a slight increase in order parameter and motion parameter in thrombin-aggregated platelets. Judging from sodium dodecyl sulfate polyacrylamide gel electrophoresis, ticlopidine did not modify the electrophoretic pattern of platelet proteins appreciably. Ticlopidine decreased cholesterol/phospholipids molar ratio and increased slightly total amounts of proteins of the platelets. These results indicate that the inhibitory action by ticlopidine was accompanied by changes in membrane fluidity, and these changes were due to a perturbation of the membrane phospholipid core of the platelets by ticlopidine and/or its metabolites.

Animals↗
PubMed1984

Vesiculation of platelet plasma membranes. Dilauroylglycerophosphocholine-induced shedding of a platelet plasma membrane fraction enriched in acetylcholinesterase activity.

Incubation of washed rabbit platelets with suspensions of dilauroylglycerophosphocholine resulted in the shedding of vesicles without causing any appreciable leakage of cytoplasmic marker (lactate dehydrogenase) or organelle marker [( 14C]serotonin). The response was dependent on incubation time, concentration of dilauroylglycerophosphocholine and reaction temperature. Vesicles were separated from platelets and exogenous dilauroylglycerophosphocholine by a series of centrifugation steps. An average diameter of vesicles was 100-200 nm on scanning electron microscopy. Vesicles were enriched 5-fold in plasma membrane marker enzyme, acetylcholinesterase, whereas specific activities of lactate dehydrogenase and intracellular membrane marker enzyme, NADH-cytochrome c reductase were decreased in vesicles. Protein analysis by SDS-polyacrylamide gel electrophoresis showed that actin and actin-binding protein were present, while myosin was barely detectable in vesicles. Vesicles contained all phospholipid species of intact platelets and cholesterol but almost 50% of phospholipids in vesicles was dilauroylglycerophosphocholine. The phospholipid to protein ratio in vesicles was about 6.5-times higher than in intact platelets.

Acetylcholinesterase↗
PubMed1983

Spontaneous formation of a monolayer membrane from sarcoplasmic reticulum at an air-water interface.

Surface pressure was found to be produced spontaneously at the interface between air and a suspension containing fragmented sarcoplasmic reticulum (FSR) from rabbit white muscle. Large and stable surface pressure was formed only in a limited concentration range of FSR in the suspension and the pressure formation was proved to be an irreversible phenomenon, suggesting the formation of a monolayer membrane resulting from the disruption of FSR vesicles. Monolayer formation was directly confirmed by analyzing the components included in the membrane and by calculating the surface area occupied by these components. The monolayer included phospholipids, cholesterol and proteins, and appeared to originate from FSR vesicles since the molecular ratios of these components as well as the results of the SDS polyacrylamide gel electrophoresis were similar in both membranes. This phenomenon can be utilized as a method of monolayer preparation from biological membrane vesicles, and should be very useful for the reconstitution of planar biological membranes.

Air↗
PubMed1983

Spin label measurement of platelet alignment in a clot induced by isometric tension.

A spin label technique was applied to examine the alignment of platelet membranes in the platelet-fibrin clot. The ESR spectrum of the clot in the control experiment was typical of isotropically oriented membranes, while the ESR spectrum of the clot which was kept isometric was quite different from that of the control experiment. These spectra were simulated with a computer and explained to indicate that the shape of platelets in the clot was transformed to a cylindrical form under the isometric tension so that axes of all membrane cylinders were directed parallel to the generated force.

Animals↗
PubMed1982

A stable planar bilayer membrane of phospholipid supported by cellulose sheets.

A new method is reported for preparing a thin planar membrane of 1,2-distearoylsn-glycero-3-phosphocholine and egg yolk lecithin-cholesterol (molar ratio of 1:1) between a pair of cellulose sheets. This technique, developed from the method of the multilayer planar membrane preparation (Setaka, M., et al. (1979) J. Biochem. 86, 355-362; 1619-1622; (1980) J. Biochem. 88, 1819-1829), consisted of three experimental processes. First, a phospholipid monolayer was prepared at an air-water interface, then taken up on a stretched cellulose sheet. A thin lipid membrane, supported from both sides by cellulose sheets, was constructed by combining two of these lipid monolayer-cellulose sheets. The permeability coefficient of the thin lipid membrane was estimated by removing the effect of two outer cellulose sheets, and this permeability was found to be larger than those of other model membranes of a lipid bilayer, indicating that the present lipid membrane is not a perfect single lipid bilayer. However, certain experimental evidence suggests that the bulk of the phospholipids formed a bilayer between the two cellulose sheets. Since this lipid membrane is particularily stable, larger membranes can be prepared by the present method than other planar bilayer membranes of lipid, which are usually constructed inside a pin hole in a thin teflon sheet.

Cell Membrane Permeability↗
PubMed1982

Orientation of platelets on the surfaces of glass and Teflon plates as studied by a spin label technique.

Platelets were found by a spin label technique to orient on flat surfaces of glass as well as of Teflon. This kind of platelet orientation was not caused by centrifugation or partial dehydration of the membrane preparation as employed usually to make oriented planar multilayers of biological membranes on the surface of a supporting plate (1-8), but was considered to be closely related to the adhesion or the aggregation properties of platelets. The amount of oriented platelets varied depending on the platelet treatment and was estimated from a computer simulation of the observed ESR spectra to be about one-half of that of the non-oriented ones in the case of thrombin-treated platelets. This technique may be useful as a new tool to explore the adhesion or aggregation properties of platelets.

Animals↗
PubMed1980

A spin-label study of the effects of drugs on calcium release from isolated sarcoplasmic reticulum vesicles.

The effects of caffeine, thymol, and procaine on calcium release from fragmented sarcoplasmic reticulum (FSR) from rabbit skeletal white muscle were investigated by the spin label method at the organellar level. Two thiol-directed spin labels, 4-maleimide-2,2,6,6-tetramethylpiperidinooxyl and 4-(2-iodoacetamide)-2,2,6,6-tetramethylpiperidinooxyl, were used for the labeling of SR proteins. The ratio (W/S) of the weakly (W) and strongly (S) immobilized ESR signals was measured for the maleimide and iodoacetamide labeled FSR. The two labels gave different W/S values, which means that the two labels report conformational changes at different loci of SR proteins. The dependences of the W/S ratios on the concentration of the drugs showed that conformational changes of SR proteins induced by these drugs are not the same. From measurements of the distribution of 5-doxyldecanoic acid methylester between the lipid and water phases, it was found that the conformational changes of the SR proteins caused by thymol or procaine induced a disorder in local regions of the phospholipid bilayers of FSR, while such disordering was not induced by caffeine. On the other hand, caffeine and thymol showed definite effects on calcium release from FSR, while procaine did not. These results indicate that the effects of the drugs on the protein conformations can be well characterized at the organellar level by means of the spin label technique and that some specific changes in the conformations of SR proteins are necessary for calcium release from FSR.

Animals↗
PubMed1980

Permeability properties of a multilayer planar membrane.

The permeability properties of multilayer planar membranes of uniformly oriented lipids between a pair of cellulose sheets were investigated. The effect of the two cellulose sheets supporting the lipid membrane on the glucose or the Ca permeation was subtracted empirically, and values of 5 X 10(-6) and 8 X 10(-6) cm/s were thus obtained for the permeability coefficients of an egg yolk lecithin (egg PC)-cholesterol membrane of about 200 bilayers to Ca2+ and glucose, respectively. These values are discussed as compared with the permeability coefficients of other model membranes. The membrane permeability was moderately affected by the addition of chemical substances to egg PC membranes. It was reduced by the presence of cholesterol, but enhanced by the presence of isopropanol, n-butanol, or thymol in the same solution above a critical concentration of each compound. These and previous observations (8) suggest that a close correlation may exist between the permeability of the membrane and the orientation of the membrane lipids. The glucose permeation was drastically suppressed by the presence of Ca2+ (10 mM) in the sample solution with the membrane containing phosphatidylserine, but was not at all suppressed with the membrane of the egg PC-cholesterol mixture.

1-Propanol↗
PubMed1979

Construction of a multilayer planar membrane applicable to ion-transport measurement.

Multilayer planar membranes applicable to ion-transport measurements were constructed from egg yolk lecithin, egg yolk lecithin-cholesterol mixture, and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine between two tightly stretched cellulose sheets. While most of the phospholipids in the membranes were found by a spin label technique to be uniformly oriented with their long hydrocarbon chains perpendicular to the surfaces of the cellulose sheets, a small fraction of phospholipids were isotropically oriented in multilayer membranes. The amount of phospholipids with isotropic orientations decreased with increasing content of cholesterol in membranes and became zero in membranes of egg yolk lecithin-cholesterol mixture (molar ratio of 1: 0.67). The degree of orientation, S, of uniformly oriented phospholipids in membranes was also increased by adding cholesterol to the membranes. The orientation of phospholipids in membranes was rather stable in distilled water and in aqueous calcium chloride (1, 10, 100 mM), while a marked disordering of oriented phospholipids was induced in a aqueous solutions containing thymol, isopropanol, or butanol beyond certain specific concentrations. The membranes can be used for measurements of calcium permeation. An appreciable barrier function to calcium permeation was detected with these multilayer planar membranes as compared with control experiments using only cellulose sheets as membranes. A preliminary investigation suggested that changes in the orientational structure of phospholipids in the multilayer planar membranes are correlated with permeability properties of the membranes.

Biological Transport↗
PubMed1979

Multilayer planar membranes of sarcoplasmic reticulum.

Multilayer planar membranes were constructed between a pair of cellulose sheets from fragmented sarcoplasmic reticulum (FSR) as well as a mixture of egg yolk lecithin and the Ca2+-ATPase purified from FSR. Since sodium deoxycholate was used instead of organic solvents in order to dissolve phospholipids in the process of the membrane preparation, the total activity of the Ca2+-ATPase was still preserved in the planar membrane of FSR. It was also indicated using a spin label technique that the orientation of phospholipids in the planar membrane of FSR was considerably disturbed by the presence of proteins such as the Ca2+-ATPase included in FSR.

Animals↗
PubMed1977

Synthesis and micellar formation of spin-labeled lysolecithin.

A spin-labeled lysolecithin, 1-[12'-(N-oxyl-4",4"-dimethyloxazolidine)-stearoyl]-sn-glycero-3-phosphorylcholine, has been synthesized in which the spin is covalently attached to its fatty acyl chain. The electron spin resonance spectra of this lysolecithin is an aqueous solution generally showed sharp three resonance lines superposed on a broad resonance line. Investigation of changes in the signal intensity of these spectra against the concentration of lysolecithin led to the inference that the sharp lines are due to monomers of lysolecithin while the broad one to micelles. The critical micellar concentration was consistent with that evaluated from the spectral shift of a dye. In the electron spin resonance spectra obtained from spin-labeled lysolecithin solutions with various amounts of dimyristoyllecithin, the line width of broad signal arised from micellar spin-labeled lysolecithin broadened as increase of dimyristoyllecithin. The line-broadening thus observed was briefly discussed.

Colloids↗
PubMed1977

Oxygen binding to cobalt(II) proto-, deutero- and meso-porphyrin IX dimethyl ester complexes in organic solvents.

The binding of oxygen to cobalt(II) meso, deutero- and proto-porphyrin IX dimethyl esters complexed with pyridine or 2-methylimidazole was investigated at -10 degress - -60 degrees C in toluene or DMF solution, and the thermodynamic data related with the binding were presented. The oxygen affinity of cobalt meso-porphyrin complex was larger by the factor of 2.0-1.4 than those of the other complexes where oxygen affinities were not explained by a simple electron-withdrawing capability of 2,4-substituents of the porphyrin ring. The oxygen binding property was, generally, dependent on the solvent, suggesting that the solvation affects appreciably the oxygen binding to the complexes. The oxygen affinities of cobalt porphyrin complexes in various organic solvents were compared with those of their apomyoglobin complexes. The differences of oxygen affinities between both systems decreased with increasing the size of 2,4-substituents, and it was in the following order on 2,4-substituted porphyrins: Deutero greater than Proto greater than Meso. It was suggested that the 2,4-substitutent effect on the oxygen affinity of cobalt myoglobin complexes was not only caused by the direct electronic effect on the central cobalt atom, but also controlled by the stereochemical interaction between apomyoglobin and the porphyrin.

Cobalt↗
PubMed1976

Magnetic circular dichroism on the reversible oxygenation of dimethylmesoporphyrin-IX-atopyridinecobalt (II).

The magnetic circular dichroism spectra were measured for the dimethylmesoporphyrin-IX-atocobalt complexes. As expected dimethylmesoporphyrin-IX-atocobalt (III) and its pyridine complex exhibited the MCD for a typical D4h metalloporphyrins. Dimethylmesoporphyrin-IX-atocobalt (II) and its pyridine complex showed a paramagnetic effect on the MCD especially in the Soret region. A very atypical Soret MCD for the oxygenated dimethylmesoporphyrin-IX-atopyridinecobalt (II) was attributed to the existence of a CT band associated with oxygen from the similarity to the MCD for oxymyoglobin. Temperature-dependent MCD change for the cobalt (II) oxygen complex revealed the reversible oxygen binding to dimethylmesoporphyrin-IX-atopyridinecobalt (II) with KO2 of 3.2 X 10(-3) in (mmHg)-1 at 228 degrees K.

Binding Sites↗
PubMed1971

Chemical methylation of inorganic mercury with methylcobalamin, a vitamin B12 analog.

Chemical methylation of mercuric chloride with methylcobalamin has been studied. Methylated mercury was detected by gas chromatography; and analysis of the products of the reaction by thin-layer chromatography revealed that the methylation proceeded at a remarkably high rate when methylcobalamin and inorganic mercury were mixed. Dimethylmercury was an initial product of the reaction.

Chemical Phenomena↗