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At least 271 records · Page 15Linked to original sources
PubMed2004

Interaction of 3,7-diamino-2,8-dimethyl-5-phenyl phenazinium chloride with model biological membranes and reverse micelles of lipid: a spectroscopic study.

The interaction of 3,7-diamino-2,8-dimethyl-5-phenyl phenazinium chloride (Safranine T) with the aqueous as well as reverse micellar solution of a phospholipid 1,2-diacyl-sn-glycero-3-phosphocholine (Azolecithin), a major structural phospholipid in brain, comprising approx 15% of total lipid, primarily localized in grey matter have been studied by absorption and fluorescence spectroscopic studies. The results show the evidence of complex formation of the dye in the ground and in the excited state. The interaction of the dye with the lipid in reverse micellar state is more compared to that in liposomes. An attempt has been made to determine the polarity of the microenvironment of the dye in liposomes or reverse micelles from the spectral studies of the dye in different solvents of known polarity. The polarity functions of the phosphatidylcholine (PC) liposomes are slightly lower compared to that of PC reverse micelles.

Liposomes↗
PubMed2004

Simulation of a mesotrophic reservoir (Lake Pareloup) over a long period (1983-1998) using ASTER2000 biological model.

Lake Pareloup is studied since 1983. The model ASTER that simulated the ecosystem of the lake during the first phase of the study (1983-1987) has been modified. The new model, called ASTER2000 aims to improve the estimation of the trophic level and the water quality of different reservoirs. To this purpose, NH4, NO3 and O2 were added as state variables. Affluents and pumping inflow have also been considered in order to consider the evolution of the watershed inflow and the variation from year to year in rainfall and pumping inflow. We have a long data series (1983-1998) that allows testing the model under different hydro-climatic conditions. The model simulates the state variables for this period in a satisfactory way. The evolution of nutrient concentrations differences bound to year-to-year entries are well represented, which would have been impossible with the original model. The addition of variables permits to rely on a larger range of the water quality criteria. In combination with the thermal forcing (temperature and stratification) provided by the EOLE model, ASTER2000, represents a strong and easy tool which could be used on many other reservoirs. The main modification necessitated in such applications concerns the type of diatoms dominating: consumed or not by the zooplankton. It is also indispensable to have input data in line with the structure of the model.

Animals↗
PubMed2004

Electric field-driven transformations of a supported model biological membrane--an electrochemical and neutron reflectivity study.

A mixed bilayer of cholesterol and dimyristoylphosphatidylcholine has been formed on a gold-coated block of quartz by fusion of small unilamellar vesicles. The formation of this bilayer lipid membrane on a conductive surface allowed us to study the influence of the support's surface charge on the structure and hydration of the bilayer lipid membrane. We have employed electrochemical measurements and the specular reflection of neutrons to measure the thickness and water content in the bilayer lipid membrane as a function of the charge on the support's surface. When the surface charge density is close to zero, the lipid vesicles fuse directly on the surface to form a bilayer with a small number of defects and hence small water content. When the support's surface is negatively charged the film swells and incorporates water. When the charge density is more negative than -8 micro C cm(-2), the bilayer starts to detach from the metal surface. However, it remains in a close proximity to the metal electrode, being suspended on a thin cushion of the electrolyte. The field-driven transformations of the bilayer lead to significant changes in the film thicknesses. At charge densities more negative than -20 micro C cm(-2), the bilayer is approximately 37 A thick and this number is comparable to the thickness determined for hydrated multilayers of dimyristoylphosphatidylcholine from x-ray diffraction experiments. The thickness of the bilayer decreases at smaller charge densities to become equal to approximately 26 A at zero charge. This result indicates that the tilt of the acyl chains with respect to the bilayer normal changes from approximately 35 degrees to 59 degrees by moving from high negative charges (and potentials) to zero charge on the metal.

Adsorption↗
PubMed1999

Extracellular matrix protein-induced changes in human salivary epithelial cell organization and proliferation on a model biological substratum.

We have used a denuded rat tracheal preparation as a biological substratum on which to examine the growth and morphology of a salivary epithelial cell line (HSG) in vitro. In the absence of an additional coating of matrix proteins, HSG cells grew at low density on tracheae. Coating the tracheae with Vitrogen (a commercial collagen I preparation) or fibronectin promoted HSG cell growth and monolayer formation. Conversely, if a coating of Matrigel was applied, cells grew in a more organized fashion, but at low density. Generally similar results were obtained with cells grown on laminin and collagen IV but with less organization. These studies demonstrate the utility of a natural, tubular substratum for testing the influence of different matrix proteins on salivary epithelial cell behavior.

Animals↗
PubMed1980

Active site-specific reconstituted copper(II) horse liver alcohol dehydrogenase: a biological model for type 1 Cu2+ and its changes upon ligand binding and conformational transitions.

Insertion of Cu2+ ions into horse liver alcohol dehydrogenase depleted of its catalytic Zn2+ ions creates an artificial blue copper center similar to that of plastocyanin and similar copper proteins. The esr spectrum of a frozen solution and the optical spectra at 296 and 77 K are reported, together with the corresponding data for binary and ternary complexes with NAD+ and pyrazole. The binary complex of the cupric enzyme with pyrazole establishes a novel type of copper proteins having the optical characteristics of Type 1 and the esr parameters of Type 2 Cu2+. Ternary complex formation with NAD+ converts the Cu2+ ion to a Type 1 center. By an intramolecular redox reaction the cuprous enzyme is formed from the cupric enzyme. Whereas the activity of the cupric alcohol dehydrogenase is difficult to assess (0.5%-1% that of the native enzyme), the cuprous enzyme is distinctly active (8% of the native enzyme). The implications of these findings are discussed in view of the coordination of the metal in native copper proteins.

Alcohol Oxidoreductases↗
PubMed1998

Generation of reactive oxygen species from the photolysis of histidine by near-ultraviolet light: effects on T7 as a model biological system.

Near-ultraviolet (NUV) light (280-400 nm) has a variety of effects on biological systems; these effects are increased, often synergistically, in the presence of sensitizers. A variety of both man-made and naturally occurring sensitizers have been identified, but their precise roles and relative contributions to cellular damage are not yet fully established. DNA seems to be a major target and a variety of types of damage have been observed. In this report we present evidence that histidine can also act as a sensitizer of NUV. Upon NUV photolysis a variety of reactive oxygen species, including superoxide anions, hydroxyl radicals and hydrogen peroxide, are produced as determined by the effects of various scavengers. pH influences the reaction, alkaline media being most effective, as has previously been reported for the photolysis of H2O2, tyrosine, phenylalanine and tryptophan. Exposure of phage T7 to a combination of histidine and NUV leads to synergistic inactivation and scavengers of O2.-, .OH and H2O2 reduce this effect. These results point to a possible involvement of sunlight-induced histidine photolysis in cellular damage. The fact that photolysis is maximal at high pH indicates that biological effects are likely to be highly localized, e.g., at enzyme active sites.

Bacteriophage T7↗
PubMed2003

[Magnetosomes as biological model for iron binding: relaxivity determination with MRI].

PURPOSE: In vitro characterization of iron-containing bacterial particles (magnetosomes) as superparamagnetic contrast agents for MRI. MATERIAL AND METHODS: Different concentrations of magnetosomes were examined with a 1.5 T clinical whole-body MR system at 21 degrees C using the transit/receive extremity coil. Both longitudinal and transversal relaxivities (R1 and R2) of the magnetosomes were determined by an inversion recovery snapshot gradient recall echo (IR FLASH) with various inversion times and a multi echo spin echo sequence. Atomic absorption spectrometry (AAS) and electron microscopy were used as reference standard. RESULTS: Longitudinal and transverse relaxivities of the magnetosomes were calculated to be R1 = 7.688 mmol -1 s -1 and R2 = 147.67 mmol -1 s -1, respectively. The corresponding iron concentrations were determined in all dilutions using AAS, while the magnetosomes were morphologically delineated by electron microscopy. CONCLUSION: Magnetosomes represent a new and interesting class of iron-containing contrast agents warranting further evaluation in cellular cultures and animal models. Magnetosomes may be suited for displaying the vector distribution and gene expression of new molecular therapies.

Contrast Media↗
PubMed1999

Role of leaflet asymmetry in the permeability of model biological membranes to protons, solutes, and gases.

Bilayer asymmetry in the apical membrane may be important to the barrier function exhibited by epithelia in the stomach, kidney, and bladder. Previously, we showed that reduced fluidity of a single bilayer leaflet reduced water permeability of the bilayer, and in this study we examine the effect of bilayer asymmetry on permeation of nonelectrolytes, gases, and protons. Bilayer asymmetry was induced in dipalmitoylphosphatidylcholine liposomes by rigidifying the outer leaflet with the rare earth metal, praseodymium (Pr3+). Rigidification was demonstrated by fluorescence anisotropy over a range of temperatures from 24 to 50 degrees C. Pr3+-treatment reduced membrane fluidity at temperatures above 40 degrees C (the phase-transition temperature). Increased fluidity exhibited by dipalmitoylphosphatidylcholine liposomes at 40 degrees C occurred at temperatures 1-3 degrees C higher in Pr3+-treated liposomes, and for both control and Pr3+-treated liposomes permeability coefficients were approximately two orders of magnitude higher at 48 degrees than at 24 degrees C. Reduced fluidity of one leaflet correlated with significantly reduced permeabilities to urea, glycerol, formamide, acetamide, and NH3. Proton permeability of dipalmitoylphosphatidylcholine liposomes was only fourfold higher at 48 degrees than at 24 degrees C, indicating a weak dependence on membrane fluidity, and this increase was abolished by Pr3+. CO2 permeability was unaffected by temperature. We conclude: (a) that decreasing membrane fluidity in a single leaflet is sufficient to reduce overall membrane permeability to solutes and NH3, suggesting that leaflets in a bilayer offer independent resistances to permeation, (b) bilayer asymmetry is a mechanism by which barrier epithelia can reduce permeability, and (c) CO(2) permeation through membranes occurs by a mechanism that is not dependent on fluidity.

Acetamides↗
PubMed1993

The impact of the pre-treatment interval on antimicrobial efficacy in a biological model.

The impact of pre-treatment intervals on the antipseudomonal efficacy of gentamicin, ticarcillin and ceftazidime was studied in an experimental thigh infection model in normal and granulocytopenic mice. Human-equivalent doses were used for simulating human pharmacokinetic profiles of the two study beta-lactam drugs. A lethal inoculum of a virulent strain of Pseudomonas aeruginosa was injected into the thigh muscle. Treatment was started at various post-infection intervals. Antimicrobial efficacy was assessed by determinations of surviving organisms at the site of infection, and plasma drug concentrations were determined in the same mice. The age of infection had a substantial impact on antipseudomonal efficacy of the three study drugs even though high, brief supra-MIC concentrations of gentamicin and persistent supra-MIC concentrations of the beta-lactam drugs were obtained. A pre-treatment interval of six or more hours abolished the bactericidal effect of all three study drugs despite accumulation of the drugs to multiple-MBC plasma concentrations. We believe that the impact of pre-treatment intervals on antimicrobial efficacy is of paramount importance for the interpretation of antimicrobial activity studies in experimental models of infection, although the mechanisms remain to be elucidated.

Agranulocytosis↗
PubMedDate not supplied

Experimental diabetes and the inner ear. A proposed biologic model.

Experimental diabetes was induced in 28 healthy chinchillas by the intravenous injection of Streptozotocin. Five chinchillas were used as controls. It was noted that a dose of 60 mg/kg body weight produced a noninsulin-dependent diabetes in adult chinchillas of mean weights of 393 gm. The chinchilla is proposed as a suitable animal model for the study of experimental diabetes because of the many attributes it possesses. A method of producing experimental diabetes is described. A method of anatomical display was utilized that allowed a detailed longitudinal study of the entire cochlear partition without sacrificing the stria vascularis and Reissner's membrane. The study did not yield any new histopathologic data concerning the nature of diabetes in the inner ear. In all likelihood this is, among other things, a factor of the mild severity of diabetes induced and the short duration of this study.

Animals↗