Decrease In Microviscosity Research Articles

Unraveling Microviscosity Changes Induced in Cancer Cells by Photodynamic Therapy with Targeted Genetically Encoded Photosensitizer

Background: Despite the fundamental importance of cell membrane microviscosity, changes in this biophysical parameter of membranes during photodynamic therapy (PDT) have not been fully understood. Methods: In this work, changes in the microviscosity of membranes of live HeLa Kyoto tumor cells were studied during PDT with KillerRed, a genetically encoded photosensitizer, in different cellular localizations. Membrane microviscosity was visualized using fluorescence lifetime imaging microscopy (FLIM) with a viscosity-sensitive BODIPY2 rotor. Results: Depending on the localization of the phototoxic protein, different effects on membrane microviscosity were observed. With nuclear localization of KillerRed, a gradual decrease in microviscosity was detected throughout the entire observation period, while for membrane localization of KillerRed, a dramatic increase in microviscosity was observed in the first minutes after PDT, and then a significant decrease at later stages of monitoring. The obtained data on cell monolayers are in good agreement with the data obtained for 3D tumor spheroids. Conclusions: These results indicate the involvement of membrane microviscosity in the response of tumor cells to PDT, which strongly depends on the localization of reactive oxygen species attack via targeting of a genetically encoded photosensitizer.

Cardiomyocyte mitochondrial respiration and microviscosity in rats of different ages in heart failure

Highlights. Heart failure in older age groups is an urgent medical and social issue. Mitochondrial dysfunction is a key link in the pathogenesis of heart failure. In this study we have demonstrated a decrease in mitochondrial respiratory function in old rats. In this age group, the development of heart failure is accompanied by a further decrease in respiratory control. An increase in the mitochondrial microviscosity in older animals may affect the activity of respiratory chain enzymes in heart failure.Aim. To study the respiratory activity and mitochondrial membrane microviscosity of cardiomyocyte of rats of different ages with heart failure.Methods. The study involved 22 2- and 15-month-old male Wistar rats. The animals were divided into 4 groups: 2 groups of intact animals of both ages (n = 12) and 2 groups of rats with isadrine model of heart failure (HF) (n = 10). HF was modeled by two subcutaneous injections of isoproterenol hydrochloride (170 mg/kg) at interval of 24 hours. Mitochondrial respiratory activity was assessed using respiratory control coefficient. The microviscosity of mitochondrial membranes was evaluated by eximerization coefficients of pyrene-based fluorescent probe in areas of protein-lipid and lipid-lipid contact. Comparative statistical analysis of independent groups was performed using the nonparametric Mann-Whitney test.Results. A decrease in mitochondrial respiratory control in older rats was shown in comparison with young animals. In the HF model, inter-age difference increases, but at the same time, in younger rats, the development of HF is not accompanied by significant changes in mitochondrial respiratory control. An age dependent decrease in the microviscosity of mitochondrial membranes in the area of protein-lipid and lipid-lipid interaction was revealed. In younger rats, the development of HF is characterized by a significant increase in microviscosity in the area of protein-lipid and lipid-lipid contact. In older rats, the development of the pathology is characterized by a significant decrease in microviscosity in the area of protein-lipid interaction.Conclusion. Multidirectional age-related changes in cardiomyocyte mitochondria of rats with heart failure were revealed. It was shown that mitochondria in younger rats retain their functional activity in the HF model unlike older rats.

Photogenerated Radical Pair between Flavin and a Tryptophan-Containing Transmembrane-Type Peptide in a Large Unilamellar Vesicle.

Electron-transfer (ET) reactions in biological systems, such as those with magnetic sensors based on flavoproteins and electron transport at biomembrane interfaces, are interesting and important issues that require understanding. As a model system of flavoproteins in biomimetic environments, we report the dynamics of the radical pair generated by photoinduced ET between riboflavin tetrabutylate (RFTB) and tryptophan (Trp) residues in a transmembrane-type polypeptide, both of which are distributed in a large unilamellar vesicle of 1,2-dimyristoyl-sn-glycero-3-phosphocholine. The Trp residues locate near the hydrophilic membrane interface, as confirmed by a dual-fluorescence quenching assay. The fluorescence and transient absorption upon photoexcitation of RFTB indicate that ET from both the singlet and triplet excited states occurs at the hydrophilic interface, whereas the RFTB in the hydrophobic region does not contribute to ET. The ET efficiency and the magnetic field effect (MFE) on the RFTB anion increase significantly above the gel-to-liquid crystal phase transition temperature due to a decrease in microviscosity. The MFE analysis indicates that the radical pair generated from the triplet ET channel exhibits a long lifetime as those in micellar systems due to the strong cage effect of the vesicle.

Morphological changes of the red blood cells treated with metal oxide nanoparticles

The toxic effect of Al2O3, SiО2 and ZrО2 nanoparticles on red blood cells of Wistar rats was studied in vitro using the atomic force microscopy and the fluorescence analysis. Transformation of discocytes into echinocytes and spherocytes caused by the metal oxide nanoparticles was revealed. It was shown that only extremely high concentration of the nanoparticles (2mg/ml) allows correct estimating of their effect on the cell morphology. Besides, it was found out that the microviscosity changes of red blood cell membranes treated with nanoparticles began long before morphological modifications of the cells. On the contrary, the negatively charged ZrO2 and SiO2 nanoparticles did not affect ghost microviscosity up to concentrations of 1μg/ml and 0.1mg/ml, correspondingly. In its turn, the positively charged Al2O3 nanoparticles induced structural changes in the lipid bilayer of the red blood cells already at a concentration of 0.05μg/ml. A decrease in microviscosity of the erythrocyte ghosts treated with Al2O3 and SiO2 nanoparticles was shown. It was detected that the interaction of ZrO2 nanoparticles with the cells led to an increase in the membrane microviscosity and cracking of swollen erythrocytes.

The effect of natamycin on the transcriptome of conidia of Aspergillus niger

The impact of natamycin on Aspergillus niger was analysed during the first 8 h of germination of conidia. Polarisation, germ tube formation, and mitosis were inhibited in the presence of 3 and 10 μM of the anti-fungal compound, while at 10 μM also isotropic growth was affected. Natamycin did not have an effect on the decrease of microviscosity during germination and the concomitant reduction in mannitol and trehalose levels. However, it did abolish the increase of intracellular levels of glycerol and glucose during the 8 h period of germination.Natamycin hardly affected the changes that occur in the RNA profile during the first 2 h of germination. During this time period, genes related to transcription, protein synthesis, energy and cell cycle and DNA processing were particularly up-regulated. Differential expression of 280 and 2586 genes was observed when 8 h old germlings were compared with conidia that had been exposed to 3 μM and 10 μM natamycin, respectively. For instance, genes involved in ergosterol biosynthesis were down-regulated. On the other hand, genes involved in endocytosis and the metabolism of compatible solutes, and genes encoding protective proteins were up-regulated in natamycin treated conidia.

Alterations in membrane fluidity and dynamics in experimental colon cancer and its chemoprevention by diclofenac

We examined the role of membrane fluidity and dynamics as important early events in the carcinogenic transformation of colonic epithelial cells. 1,2-Dimethylhydrazine dihydrochloride (DMH) was used to induce initial stages of colon cancer and diclofenac was used for chemoprevention. To determine alterations of membrane fluidity of rat colonic epithelial cells, fluidity (inverse of fluorescence polarization) and order parameter were studied with 1,6-diphenylhexatriene (DPH) polarization. Order parameter as well as fluorescence polarization was found to be significantly decreased, thus demonstrating an increase in the fluidity of the membrane. To further confirm the fluidity changes, microviscosity of the cell membrane was studied using pyrene excimer formation, which showed a significant decrease in microviscosity and hence elevated membrane fluidity (translational diffusion). The colonocytes were stained with merocyanine 540 (MC540) to further elaborate the changes in membrane fluidity and lipid packing. The increased number of colonocytes showing high MC540 fluorescence pointed towards the wide spaces and hence, high fluidity in the membrane after DMH treatment. Membrane dynamics studies, i.e., lipid phase separation and membrane phase state were carried out using N-NBD-PE and Laurdan, respectively. We saw a transition from the gel to a more liquid crystalline state of the membrane in the Laurdan experiment. Further more percentage quenching (%Q) value of N-NBD-PE showed less phase separation (or domain formation). Diclofenac co-administration with DMH was successful in reverting the changes observed, confirming the role of these anti-inflammatory drugs in considerable lipid affinity and consequently in the chemoprevention of early stages of colon cancer.

Poly(styrene- b-2-(N,N-dimethylamino)ethyl methacrylate) diblock copolymers: Micellization and application in the synthesis of photoluminescent CdS nanoparticles

Fluorescence studies on amphiphilic diblock copolymers of styrene and 2-(N,N-dimethylamino)ethyl methacrylate using 1,8-anilinonaphthalenesulfonate (ANS) as fluorescent probe revealed the formation of stable micelles at extremely low polymer concentrations of ∼0.05%. The micellar microenvironment was characterized by an average polarity of E T(30) = 44–48 kcal mol −1, similar to the moderately polar solvents, and extremely high microviscosity. Increase in hydrophilic: hydrophobic ratio of the copolymers resulted in an increase in the average polarity and decrease in microviscosity. The micelles proved to be excellent hosts for the synthesis and stabilization of photoluminescent CdS nanoparticles with a high degree of quantum confinement and broad photoluminescence, dominated by trap-state emission. Moreover, the size and size-related steady-state optical properties of CdS nanoparticles were significantly dependent on the microenvironment of the host micelle. In contrast, the photoluminescence dynamics of the nanoparticles, involving time-scales from 100 ps to 100 ns, are similar in all cases. Interestingly, the nanoparticles exhibit a large time-dependent Stokes shift, 75% of which is complete within the first ∼100 ps after the excitation. The extremely rapid Stokes shift is attributed to the decay of the initially formed band-edge excitons in a time-scale too fast to be affected by the microenvironment surrounding the particle.

Spectra and dynamics of an ionic styryl dye in reverse micelles

The interesting influence on the photophysics of an intramolecular donor–acceptor system 2-(4-(dimethylamino) styryl)-1-methylpyridinium iodide (DASPMI), a known selectively staining agent of mitochondria in living cells, by the monodispersed biomimicking nanocavities formed by the anionic sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/n-heptane and the cationic benzyl-n-hexadecyl dimethylammonium chloride (BHDC)/benzene reverse micelles and also water-in-oil (n-heptane/(AOT)/water or benzene/(BHDC)/water) have been reported in this paper. Red shift of DASPMI emission in AOT with increasing water pool size ( W = [H 2O]/[surfactant]) indicates that the probe molecule moves towards core and the blue shift in BHDC in the same condition is indicative of the probe remaining away from the core. The partition constant K p in two RMs correlate well with the position of emitting probe DASPMI in RMs interface and it corresponds nicely with the values obtained from anisotropy data. Reduced quantum yield of TICT emission with increasing pool size ( W) in AOT due to non-radiative decay through hydrogen bonding suggests that the acceptor group is at the interface directed towards water pool. In AOT decreasing anisotropy along with active non-radiative channel confirm the presence of the probe at the water/AOT interface. The rotational restriction experienced by DASPMI in anionic reverse micelle decreases with increasing hydration. The in situ measurements of micropolarity and microviscosity around the probe with increasing W show enhanced micropolarity and a decrease in microviscosity. Increased emission quenching by Cu 2+ is due to counterion exchange of Cu 2+ by Na + at the micellar interface and due to increased local concentration of Cu 2+. It again confirms that the probe molecule does not penetrate into the core rather it binds at the interfacial region. The unaffected TICT emission in fluorescence quenching study in BHDC confirms position of probe away from the core.

Effect of Melafen on functional efficiency of mitochondrial membranes from sugar beet taproots

Mitochondria were isolated from sugar beet (Beta vulgaris L) taproots and incubated in the presence of low concentrations of Melafen (2 × 10−9 and 4 × 10−12 M). This treatment of mitochondrial membranes induced an appreciable decrease in microviscosity of superficial lipids in the lipid bilayer and a parallel increase in microviscosity of the deeply immersed lipid regions adjacent to membrane proteins. Melafen had no effect on fluorescence of lipid peroxidation products in membranes of freshly prepared mitochondria but declined this fluorescence to control values in artificially aged mitochondria. Melafen raised the maximum rates for oxidation of NAD-dependent substrates, elevated the efficiency of oxidative phosphorylation, and activated electron transport in the terminal (cytochrome oxidase) step of mitochondrial respiratory chain, which implies the activation of energy metabolism within the cell. The acceleration of electron transport through the terminal step of mitochondrial respiratory chain was apparently accompanied by retardation of lipid peroxidation, which prevented impairment of mitochondrial membranes under stress conditions. A proposal is put forward that some properties of Melafen are favorable for adaptogenesis because its effects on mitochondrial energy metabolism depended on the functional state of mitochondria.

Lipid composition determines interaction of liposome membranes with Pluronic L61

Triblock copolymers of ethylene oxide (EO) and propylene oxide (PO) of EO n/2PO mEO n/2 type (Pluronics) demonstrate a variety of biological effects that are mainly due to their interaction with cell membranes. Previously, we have shown that Pluronics can bind to artificial lipid membranes and enhance accumulation of the anti-tumor drug doxorubicin (DOX) inside the pH-gradient liposomes and transmembrane migration (flip-flop) of NBD-labeled phosphatidylethanolamine in the liposomes composed from one component—lecithin. Here, we describe the effects caused by insertion of other natural lipids in lecithin liposomes and the significance of the lipid composition for interaction of Pluronic L61 with the membrane. We used binary liposomes consisting of lecithin and one of the following lipids: cholesterol, phosphatidylethanolamine, ganglioside GM1, sphingomyelin, cardiolipin or phosphatidic acid. The influence of the additives on (1) membrane microviscosity; (2) binding of Pluronic L61; (3) the copolymer effect on lipid flip-flop and membrane permeability towards DOX was studied. The results showed that insertion of sphingomyelin and cardiolipin did not influence membrane microviscosity and effects of Pluronic on the membrane permeability. Addition of phosphatidic acid led to a decrease in microviscosity of the bilayer and provoked its destabilization by the copolymer. On the contrary, cholesterol increased microviscosity of the membrane and decreased binding of Pluronic and its capacity to enhance flip-flop and DOX accumulation. Analogous tendencies were revealed upon incorporation of egg phosphatidylethanolamine or bovine brain ganglioside GM1. Thus, a reverse dependence between the microviscosity of membranes and their sensitivity to Pluronic effects was demonstrated. The described data may be relevant to mechanisms of Pluronic L61 interaction with normal and tumor cells.

Quantification of lipid bilayer effective microviscosity and fluidity effect induced by propofol

Electron spin resonance (ESR) spectroscopy with nitroxide spin probes was used as a method to probe the liposome microenvironments. The effective microviscosities have been determined from the calibration of the ESR spectra of the probes in solvent mixtures of known viscosities. In the first time, by measuring ESR order parameter ( S) and correlation time ( τ c) of stearic spin probes, we have been able to quantify the value of effective microviscosity at different depths inside the liposome membrane. At room temperature, local microviscosities measured in dimyristoyl- l-α phosphatidylcholine (DMPC) liposome membrane at the different depths of 7.8, 16.95, and 27.7 Å were 222.53, 64.09, and 62.56 cP, respectively. In the gel state (10 °C), those microviscosity values increased to 472.56, 370.61, and 243.37 cP. In a second time, we have applied this technique to determine the modifications in membrane microviscosity induced by 2,6-diisopropyl phenol (propofol; PPF), an anaesthetic agent extensively used in clinical practice. Propofol is characterized by a unique phenolic structure, absent in the other conventional anaesthetics. Indeed, given its lipophilic property, propofol is presumed to penetrate into and interact with membrane lipids and hence to induce changes in membrane fluidity. Incorporation of propofol into dimyristoyl- l-α phosphatidylcholine liposomes above the phase-transition temperature (23.9 °C) did not change microviscosity. At 10 °C, an increase of propofol concentration from 0 to 1.0×10 −2 M for a constant lipid concentration mainly induced a decrease in microviscosity. This fluidity effect of propofol has been qualitatively confirmed using merocyanine 540 (MC540) as lipid packing probe. Above 10 −2 M propofol, no further decrease in microviscosity was observed, and the microviscosity at the studied depths (7.8, 16.95, and 27.7 Å) amounted 260.21, 123.87, and 102.27 cP, respectively. The concentration 10 −2 M was identified as the saturation limit of propofol in dimyristoyl- l-α phosphatidylcholine liposomes.

Thermodynamics and Micellar Properties of Tetradecyltrimethylammonium Bromide in Formamide–Water Mixtures

The effect of formamide on the micellization of tetradecyltrimethylammonium bromide has been investigated by conductance and fluorescence probe experiments. The critical micelle concentration and the degree of counterion dissociation of micelles were obtained from conductance measurements in the temperature range of 20 to 40°C. It was found that these two parameters increase with both temperature and formamide content in the solvent system. The thermodynamic parameters of micellization were estimated using the equilibrium model of micelle formation. The standard free energy of micellization was found to be negative in all cases and becomes less negative as the formamide content in the mixed solvent increases, but it is roughly independent of temperature. Although the entropic contribution was found to be larger than the enthalpy one, in particular at lower temperatures, an enthalpy–entropy compensation effect was observed for all systems. Micellar aggregation numbers were determined by the static quenching method, using pyrene as a probe and cetylpyridinium chloride as a quencher. The observed decrease in the micelle aggregation number, which is controlled by the increase in the surface area per headgroup, was attributed to an enhanced solvation in formamide rich solvent mixtures. Changes in the pyrene 1:3 ratio index, indicating a more polar environment, are consistent with an increased micellar solvation. Fluorescence polarization of both coumarin 6 and fluorescein are indicative of a decrease in microviscosity with cosolvent addition. The data on fluorescence anisotropy of coumarin 6 were analyzed using the wobbling in cone model. Data indicated the formation of micelles with a less ordered structure as the formamide increases in the solvent system.

The effect of alkyl core structure on micellar properties of poly(ethylene oxide)-block-poly( l-aspartamide) derivatives

Block copolymers based on fatty acid esters of poly(ethylene oxide)-block-poly(hydroxy alkyl l-aspartamide) were prepared and characterized by 1H-NMR. The structure of the core-forming block was changed through application of different lengths of the poly( l-aspartamide) (PLAA) block, spacer group or fatty acid and varying the substitution level of the side chain on the polymeric backbone. Transmission electron microscopy and fluorescent probe studies provided evidence for the formation of supramolecular core/shell architectures with nanoscopic dimensions. The same techniques were used to study the effect of hydrophobic block structure on micellar size, critical micelle concentration (CMC), core polarity and viscosity of the polymeric micelles. Among the structural factors studied, it was revealed that the length of the PLAA block and the level of fatty acid attached to the polymeric backbone are the major factors affecting micellar properties. An increase in micellar size and reduction in CMC were observed when the level of fatty acid attachment to the polymeric backbone was raised. The elongation of the PLAA block, on the other hand, resulted in an increase in micellar size and core viscosity. Micellar size was the only characteristic being affected by the length of the attached fatty acid. However, a decrease in microviscosity was revealed when behenic acid (22 carbons) was attached to the core-forming block in a high level of substitution. The length of spacer group was also found to be a useful means by which the level of side chain attachment could be controlled. Chemical tailoring of the core structure in polymeric micelles may be used as an efficient means to change micellar properties. As a result, nanoscopic, spherical and stable micelles with improved core properties may be achieved to insure efficient loading and controlled release of an individual drug from the delivery system.

Gel–sol transition in κ-carrageenan systems: microviscosity of hydrophobic microdomains, dynamic rheology and molecular conformation

The effect of gel–sol transition in κ-carrageenan systems on the microviscosity of hydrophobic microdomains, as well as its relation to macroscopic rheology and molecular conformation, was studied in κ-carrageenan systems. The microdomains were probed by 1,3-di(-1-pyrenyl)propane (P3P) for which the excimer intensity ( I e) provides relative measures of the microviscosity in the immediate probe surroundings. In particular the applicability of P3P to monitor the gel–sol transition was proved, the results showing a dramatic decrease in microviscosity in the vicinity of the transition point. The corresponding changes in rheological properties and carrageenan conformation were investigated by dynamic viscometry (DV) and optical rotation (OR), respectively. The temperature of onset of the transition as indicated by the microviscosity data ( T 0) was found to correlate well with the OR and DV-results. The application of microviscosity and OR-measurements allowed an estimation of the helical content at T 0 to be determined. P3P-data indicate a microenvironment viscosity for the probe sites in the κ-carrageenan system comparable to that found in SDS micelles.

Physicochemical Studies on Reverse Micelles of Sodium Bis(2-ethylhexyl) Sulfosuccinate at Low Water Content

Studies on aggregation of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in isooctane at low water content were carried out. The critical micelle concentration (cmc) thermodynamic parameters were determined at various temperatures. The observations suggested that the micellization process was endothermic in nature and that it is mainly an entropic process. The cmc was also determined at various R values (R < 3) and it was found that cmc increases with increasing R. The aggregation number was determined at the R value of 1.6. From the pyrene and ANS binding studies, the microviscosity and micropolarity changes on the onset of micellization are well characterized. Spectral studies with ANS indicate a decrease in microviscosity on increase in R value. ANS fluorescence was monitored in the presence of additives like acrylamide, KI3, and tetrabutylammonium iodide. The iodide-based additives lead to quenching of fluorescence of ANS with concomitant red shift in the λem suggesting decreased microviscosity and micropolarity. Acrylamide was shown to increase the polarity by the ANS spectral features. These findings led to the conclusions that the positive ΔHm° values arise mainly from the dismantling of hydrated ions in the quasi-lattice of AOT interior. With an increase in temperature, immobilized structured states of water get destructured, which ultimately leads to favoring the aggregation process.

Molecular interactions between lipids and some steroids in a monolayer and a bilayer. 2

Molecular interactions between L-α-dipalmitoylphosphatidylcholine (DPPC) and some steroids having different hydrophilic groups in a monolayer and in a bilayer are investigated in terms of surface pressure, permeability, and microviscosity. The steroids used in this study are stigmasterol, 4,22-stigmastadien-3-one (stadiene), and stigmasterol acetate (acetate). The collapse pressures for the mixed monolayer of DPPC with various steroids depend upon the molar ratio (X) and types of hydrophilic groups in steroids. A one-stage collapse is observed for X ≤ 0.5 of stigmasterol, X ≤ 0.3 of stadiene and acetate, whereas a two-stage collapse is seen in other molar ratios of the steroids. The mole fraction within which liposomes are formed is dependent upon the types of hydrophilic group within the steroids. In comparing monolayer and bilayer membranes (liposomes), liposomes are formed at the mole fraction of steroids which have a one-stage collapse in DPPC/steroid mixed monolayer. The permeability ofthe bilayer membrane decreases with increasing cohesive force between DPPC and steroids, but increases with a decrease in microviscosity near the hydrophilic portions, in the following order : stigmasterol < stadiene < acetate. This study demonstrates that the permeability of liposomes is dependent upon the hydrophilic group of the steroids, and the stability of the liposomes increases with an increase in the cohesive forces between DPPC and the steroids.

Involvement of reactive oxygen species in emotional stress: A hypothesis based on the immobilization stress-induced oxidative damage and antioxidant defense changes in rat brain, and the effect of antioxidant treatment with reduced glutathione

We examined the oxidative damage and antioxidant defense changes with immobilization-induced emotional stress in the rat brain. Though superoxide dismutase activity remained unchanged, brain peroxidation was significantly accelerated by the immobilization stress. Membrane fluidity study with spin labeling in brain cortical membrane showed that immobilization stress induced an increase in microviscosity of membrane layer near the surface and in the ordering of membrane proteins but a decrease in microviscosity at the core of the membrane bilayer. The Na, K-ATPase activity decreased whereas the levels of some monoamines and their metabolites increased along with their metabolic rate. The administration of reduced glutathione showed a protective effect on the immobilization stress-induced stomach bleeding, oxidative damage and abnormal changes in the brain antioxidant defenses. Based on these results and on previous reports, we hypothesize that immobilization stress may induce the formation of reactive oxygen species which weakens the brain antioxidant defenses and induces oxidative damage. The antioxidant administration of reduced glutathione provides further evidence to support the above hypothesis, and also may provide clues in the search for a rational therapy to emotional stress. A possible correlation of emotional stress to aging is also discussed.

Ionizing radiation-induced structural modification of human red blood cells

The effect of gamma radiation on red blood cells have been examined using a spin labeling method. For this purpose two spin labels were used to monitor membrane fluidity: methyl 5-doxylpalmitate (Met 5-DP) and methyl 12-doxylstearate (Met 12-DS). The irradiation of red cells with the doses of 200 and 500 Gy caused decrease of microviscosity in certain regions of lipid bilayer (as indicated by Met 5-DP and Met 12-DS spectra) but did not affect lipid order parameter. The behavior of two other spin labels, maleimide(4-maleimido-2,2,6,6-tetramethylpiperidine-1-oxyl) and TEMPONE (4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl) indicated: 1) conformational changes of membrane proteins, 2) modification of cell internal peptides and proteins, 3) decreased internal viscosity of red blood cells.

Decrease in microviscosity and cholesterol content of rat liver plasma membranes after chronic ethanol feeding.

This investigation was performed to determine whether chronic ethanol feeding alters the lipid composition or the fluidity of liver plasma membranes. Male Sprague-Dawley rats were pair-fed nutritionally adequate liquid diets containing ethanol as 36% of energy or an isocaloric amount of carbohydrate for 4-5 wk. Contrasting with other membranes, chronic ethanol feeding resulted in an increase in hepatic plasma membrane fluidity as assessed by fluorescence anisotropy. This alteration was associated with a decrease in plasma membrane cholesterol content.

In vitro effects of psychotropic agents on the microviscosity of platelet membranes.

Normal platelet membranes were exposed in vitro to a variety of psychotropic agents, including chlorpromazine, fluphenazine, haloperidol, imipramine, and lithium. Changes in microviscosity of the hydrocarbon layer of the drug-exposed membranes were determined by steady-state fluorescence polarization measurements, employing the fluorescent probe 1,6-diphenyl 1,3,5-hexatriene (DPH). Concentrations of the phenothiazines chlorpromazine and fluphenazine above 200 nM produced significant increases in microviscosity, while haloperidol produced a small but consistent decrease in microviscosity in the concentration range of 200 nM to 200 microM. Imipramine and lithium were without effect. The phenothiazine-induced increase in microviscosity was apparently dependent upon the structure of the phenothiazine nucleus; side chain structure was less important to this effect.