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Biomedical subjects

T E Thompson

Publications and source records attributed to T E Thompson.

At least 109 records · Page 6Linked to original sources
PubMed1978

Studies on the anomalous thermotropic behavior of aqueous dispersions of dipalmitoylphosphatidylcholine-cholesterol mixtures.

Examination of the thermotropic behavior of aqueous dispersions of dipalmitoylphosphatidylcholine-cholesterol mixtures by high-sensitivity scanning calorimetry has revealed that the phospholipid gel to liquid-crystalline phase transition consists of two components. One, a relatively sharp transition centered at 39.6-40.7 degrees C, exhibits a transition enthalpy change which decreases linearly with increasing cholesterol content, approaching zero at a cholesterol content of about 25 mol %. The other, a broad, lower intensity transition centered at approximately 41.5 degrees C for cholesterol concentrations of 20 mol %, displays an enthalpy change which is maximal at about 20-25 mol % cholesterol and which decreases as the cholesterol content decreases to zero or increases above 25 mol %. The origin of these two transitions is discussed in terms of a separation of these lipid mixtures into cholesterol-rich and cholesterol-poor domains.

Calorimetry, Differential Scanning↗
PubMed1978

Interaction of vesicular stomatitis virus with lipid vesicles: depletion of cholesterol and effect on virion membrane fluidity and infectivity.

Interaction with excess unilamellar phosphatidylcholine (PC) vesicles resulted in depletion of as much as 90% of the cholesterol from the membrane of intact vesicular stomatitis (VS) virus. The cholesterol depletion was not significantly influenced by the proteolytic removal of virion glycoprotein spikes, but it was temperature dependent. Cholesterol depletion caused substantial reduction in anisotropy of the VS virion membrane as measured by fluorescence depolarization of the lipophilic probe 1,6-diphenyl-1,3,5-hexatriene; residual adsorbed vesicles represent a significant factor in this apparent increase in virion membrane fluidity. Interaction with PC vesicles resulted in a substantial loss of VS viral infectivity as measured by plating efficiency on L-cell monolayers. Reduction in infectivity appeared to be related to temperature-dependent depletion of virion cholesterol by PC vesicles. Interaction of VS virions with cholesterol-containing PC vesicles resulted in significantly less decline in infectivity, but attempts to restore cholesterol and infectivity to depleted VS virions were unsuccessful. Depletion of virion cholesterol apparently results through collision with PC vesicles rather than movement of cholesterol monomers or micelles through the aqueous phase, because PC vesicle-virion interaction in the presence of cholesterol oxidase did not result in substantial oxidation of translocated cholesterol.

Cholesterol↗
PubMed1977

Exchange of cytochrome b5 between phospholipid vesicles.

Detergent-extracted cytochrome b5, which binds readily to phosphatidylcholine vesicles, has been shown to exchange between vesicles by the following experiments. When preformed cytochrome b5-vesicle complexes are incubated with fresh vesicles a new species arises which sediments in the analytical ultracentrifuge with a rate intermediate between those of the original components. When the same mixture is subjected to free boundary electrophoresis no slow moving component corresponding to pure vesicles is seen. The results of sucrose density gradient centrifugation are also consistent with the conclusion that cytochrome b5 exchanges between vesicles. The possibility that the above results were produced by vesicle fusion or aggregation was eliminated by light-scattering studies and a direct assay for vesicle fusion. The ability of cytochrome b5 to exchange between lipid structures has important implications not only in the cytochrome b5-lipid system but also in enzymatic reactions in which cytochrome b5 is involved.

Ascorbic Acid↗
PubMed1977

A nuclear magnetic resonance study of sphingomyelin in bilayer systems.

The physical properties of small single-walled vesicles composed of the zwitterionic phospholipid sphingomyelin have been studied using 1H and 31P nuclear magnetic resonance spectroscopy. The temperature variation of proton line widths and spin-lattice relaxation times and the chemical shift behavior for sphingomyelin vesicles are compared with results previously determined for phosphatidylcholine vesicles. Differences between the two systems are interpreted as indications of the presence of both inter- and intramolecular hydrogen bonding in sphingomyelin bilayers.

Animals↗
PubMed1977

A simple method for the preparation of homogeneous phospholipid vesicles.

A new method is described for the preparation of homogeneously sized, single-lamellar phospholipid vesicles. This method, wich is based on differential high-speed ultracentrifugation, has the advantages of a higher vesicle yield without dilution and rapidity of preparation when compared to the molecular-sieve technique. The homogeneity of vesicle dispersions, prepared by this new method, is examined by several physical techniques and found to be comparable to the best samples prepared by molecular-sieve chromatography.

Diffusion↗
PubMed1976

Fluorescence depolarization studies of phase transitions and fluidity in phospholipid bilayers. 1. Single component phosphatidylcholine liposomes.

The fluorescence depolarization associated with the hydrophobic fluorescent probe 1,6-diphenyl-1,3,5-hexatriene is used to monitor the changes in fluidity accompanying the gel-liquid crystalline phase transition in synthetic phosphatidycholine dispersions. The parameters of the phase transition are determined for both large, multilamellar liposomes and small, single-lamellar vesicles. These parameters are compared with those obtained using other techniques. In addition, the data are interpreted in terms of two limiting molecular models, which in turn offer insight into the structural differences between multilammelar liposomes and small vesicles.

Binding Sites↗
PubMed1976

Fluorescence depolarization studies of phase transitions and fluidity in phospholipid bilayers. 2 Two-component phosphatidylcholine liposomes.

The fluorescence deplorarization associated with the hydrophobic fluorescent probe 1,6-diphenyl-1,3,5-hexatriene is used to monitor changes in fluidity accompanying the gel-liquid crystalline phase transition in phosphatidylcholine dispersions. In this way, the parameters of the phase transition are determined for both large, multilamellar liposomes and small, single-lamellar vesicles composed of three mixtures of phosphatidycholines: dimyristoyl-dipalmitoyl, dimyristoyl-distearoyl, and dioleyl-dipalmitoyl. Phase diagrams for these mixed-lipid vesicles are constructed by plotting the delimiting temperatures of the phase transition vs. the lipid compostion of the vesicle. The phase diagrams are interpreted to suggest that the miscibilities of the lipids studied are markedly different in small, single-lamellar vesicles and large multilamellar liposomes. These results are discussed in terms of the effects of high curvature on the structure of biological membranes.

Binding Sites↗
PubMed1976

A calorimetric study of the thermotropic behavior of aqueous dispersions of natural and synthetic sphingomyelins.

A recently developed differential scanning calorimeter has been used to characterize the thermotropic behavior of aqueous dispersions of liposomes containing sphingomyelin. Liposomes derived from sheep brain sphingomyelin exhibit a broad gel-liquid crystalline phase transition in the temperature range of 20-45 degrees C. The transition is characterized by maxima in the heat capacity function at 31.2 and 37.1 degrees C and a total enthalpy change of 7.2 +/-0.4 kcal/mol. Beef brain sphingomyelin liposomes behave similarly but exhibit heat capacity maxima at 30, 32, and 38 degrees C and a total enthalpy change of 6.9 kcal/mol. The thermotropic behavior of four pure synthetic sphingomyelins is reminiscent of multilamellar lecithin liposomes in that a single, sharp, main transition is observed. Results obtained for liposomes containing mixtures of different sphingomyelins are complex. A colyophilized mixture of N-palmitoylsphingosinephosphorylcholine, N-stearoylsphingosinephosphorylcholine, and N-lignocerylsphingosinephosphorylcholine in a 1 : 1 : 1 mol ratio exhibits a single transition with a Tm below that observed for the individual components. On the other hand a 1 : 1 mixture of N-stearoylsphingosinephosphorylcholine and 1-palmitoyl-2-oleylphosphatidylcholine exhibits three maxima in the heat capacity function. It is clear from these results that the thermotropic behavior of sphingomyelin-containing liposomes is a complex function of the exact composition. Furthermore, it appears that the behavior of the liposomes derived from natural sphingomyelins cannot be explained in terms of phase separation of the individual components.

Animals↗
PubMed1976

Effects of paramagnetic shift reagents on the 13C nuclear magnetic resonance spectra of egg phosphatidylcholine enriched with 13C in the N-methyl carbons.

Effects of paramagnetic shift reagents on the 13C NMR spectra obtained from single-walled vesicle dispersions of egg phosphatidylcholine enriched with 13C in the N-methyl carbons are investigated. Spectra obtained at 25.1 MHz show that, at Yb3+ to phospholipid molar ratios as low as 0.06, complete resolution of the N-methyl carbon resonances is obtained from molecules on the inner and outer faces of the vesicle bilayer. No precipitation of the vesicles is caused by Yb3+ at these concentrations nor is appreciable line broadening observed. Other paramagnetic shift reagents frequently used in proton NMR investigations of phosphatidylcholine vesicles do not give complete separation of the N-methyl 13C signals from the two bilayer surfaces. K3Fe(CN)b,Eu3+, and Pr3+ cause precipitation of the phosphatidylcholine vesicles at concentrations, which give only incomplete resolution of these signals. T1 measurements of the resonances separated by Yb3+ indicate that the choline groups on the inner bilayer surface are less mobile than are the same groups in the outer surface. Gated proton decoupling measurements, which show that the nuclear Overhauser effect is 2.8 +/- 0.1, indicate that the dominant mode of relaxation is dipolar interaction.

Carbon Isotopes↗
PubMed1976

A calorimetric and fluorescent probe study of the gel-liquid crystalline phase transition in small, single-lamellar dipalmitoylphosphatidylcholine vesicles.

The results of a calorimetric and fluorescent probe study of the thermotropic behavior of various types of dispersions of dipalmitolphosphatidylcholine bilayer vesicles are reported. Bangham-type, multilamellar vesicles exhibit tow distinct phase transitions at 34.6 and 41.2 degrees C. On the other hand, single-lamellar spherical vesicles appear to exhibit a single transition at 37 degrees C. The single-lamellar vesicles are thermodynamically unstable below 27 degrees C and slowly transform into a multilamellar structure with a single phase transition of 41.2 degrees C. These transformed structures resemble, but are not identical with, Bangham-type vesicles. An experimentally testable thermodynamic and kinetic model based upon these results is developed.

Calorimetry↗
PubMed1976

Nuclear pores in the spermatozoon of the rat.

The paper describes a hexagonal array of nuclear pores in a non-redundant region of the nuclear envelope underlying the basal surface of the rat spermatozoon head. It is concluded that intranuclear material protruding through these pores is the cause of the characteristic rows of circular 'bumps' found in surface replicas of this region.

Animals↗
PubMed1975

Transbilayer exchange of phosphatidylethanolamine for phosphatidylcholine and N-acetimidoylphosphatidylethanolamine in single-walled bilayer vesicles.

A preparation of small single-walled liposome vesicles containing a 9:1 mole ratio of phosphatidylcholine to phosphatidylethanolamine was subjected to reaction with the membrane-impermeable reagent, isethionyl acetimidate hydrochloride. This reagent converted 90% of the external phosphatidylethanolamine groups to the amidine derivative, leaving the mole ratio of unreacted phosphatidylethanolamine to phosphatidylcholine on the outside surface of the vesicle much lower than that on the inside surface. Equilibration of phosphatidylethanolamine across the bilayer was then measured as a function of time by monitoring the appearance of phosphatidylethanolamine on the outside surface utilizing the reaction of the amino groups with 2, 4, 6-trinitrobenzenesulfonic acid. The results show that no new phosphatidylethanolamine appeared on the external surface of the vesicles over a period of 12 days at 22 degrees. A conservative estimate of the precision of the measurements is +/- 10%. On this basis, the estimated half-time for the equilibration of phosphatidylethanolamine across the bilayer of these vesicles must be at least 80 days at 22 degrees.

Binding Sites↗
PubMed1975

Chloride flux in bilayer membranes: the electrically silent chloride flux in semispherical bilayers.

High resistance semispherical bilayer membranes of areas as large as 0.3 cm-2 were formed from a decane solution of synthetic diphytanoylphosphatidylcholine. These bilayers had a specific resistance of about 10-9 omega cm-2 and a specific capacitance of 0.38 mu F cm- minus 2 at 20 degrees in 0.1 M KCL. Under these conditions, chloride permeability was 6.8 times 10- minus 8 cm/sec. This electrically silen 36-Cl flux was found to be about 10-3-fold larger than the chloride current calculated from the electrical parameters of the system. The chloride flux in the bilayer was independent of the applied electrical field and was unaltered by addition of reducing agents to the ambient aqueous solutions. It was, however, substantially reduced when NO3 minus was substituted for Cl minus on the side of the bilayer initially free of 36-Cl, or if I minus was added to the aquesous phases in the concentration range of 0.001-0.1 M. These results strongly suggested that the electrically silent flux of 36-Cl is primarily a carrier mediated diffusion process in which phosphatidylcholine acts as the carrier species.

Binding Sites↗
PubMed1975

Chloride flux in bilayer membranes: chloride permeability in aqueous dispersions of single-walled, bilayer vesicles.

Aqueous dispersions of phosphatidylcholine vesicles were utilized to determine bilayer permeability to 36-Cl as a function of pH and temperature. These dispersions were comprised of single-walled vesicles, homogeneous in size, prepared by sonication of purified egg phosphatidylcholine under argon followed by fractionation on a molecular sieve. Permeability constants calculated from the inward flux of 36-Cl and the geometric parameters of these vesicles proved to be dependent on both pH and temperature. Analysis of these dependences leads to the conclusion that 36-Cl permeation in the presence of KCl is due principally to a carrier mediated exchange process involving a phospholipid-HCL complex. Net permeation by H-36-Cl may make a small contribution to the 36-Cl flux, however, studies carried out at very low chloride concentrations show that this flux is much smaller than the exchange flux. Thus chloride permeability for the exchange process is 1.5 times 10- minus 11 cmsec- minus 1 while the corresponding coefficient for the net flux of H-36-Cl is 1.0 times 10- minus 12 cm sec- minus 1 at pH 7. The activation energy for the 36-Cl exchange flux was found to be 19 plus or minus 2 kcal/mol. This value is similar to that obtained for the transbilayer "flip-flop" of phosphatidylcholine molecules in a similar system (Kornberg and McConnell, 1971). This correspondence together with the fact that the experimentally determined flux of 36-Cl agrees well with that calculated from the "flip-flop" parameters, strongly suggests that the flux of 36-Cl and "flip-flop" of phosphatidylcholine may be the same process.

Binding Sites↗