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 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rigidity of the outer hemileaflet of the plasma membrane of two prostatic carcinoma cell lines with different metastatic potential, 1-LN and 1-LN-EMS-10, was assessed by steady-state anisotropy, using a battery of fluorescent probes. The "bulk" membrane rigidity sensed by diphenylhexatriene, trimethylammonio-DPH, 1-palmitoyl-2-[DPH-ethylcarbonyl]-phosphatidylcholine, and 10-pyrenedecanoic acid indicated slightly higher rigidity in the membrane of the highly metastatic line (1-LN). This was accompanied by 26% greater mole fraction of cholesterol and 9% lower phospholipid, resulting in 40% greater cholesterol/phospholipid ratio. Phosphatidylethanolamine was increased 12%, but corresponding decreases in phosphatidylserine and phosphatidylinositol resulted in no significant change in molar ratio of choline/noncholine phospholipids. Whereas unsaturation index was slightly higher in 1-LN, fatty acids of 1-LN plasma membranes contained 15% more 18:1, 43% more 20:4, 26% more 22:4, and 38% less 18:2. Anisotropy gradients were determined for the two cell lines using a series of n-(9-anthroyloxy) fatty acid probes with n = 2, 3, 6, 7, 9, 12, and 16. Gradients differed only in position of anisotropy maxima, which occurred with n = 6, in 1-LN, and n = 7, in 1-LN-EMS-10. Possible relationships between observed anisotropy gradients and differences in membrane cholesterol and fatty acid composition are discussed.
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PMID:Membrane structural dynamics of plasma membranes of living human prostatic carcinoma cells differing in metastatic potential. 189 34

A comparison was made of ethanol's effects on the order of plasma membranes in intact cells and some isolated membrane preparations. Order was assessed by steady-state fluorescence polarization techniques using the non-permeant probe, TMA-DPH. The data show that two cultured cells, rat neonatal astroglial and N2A neuroblastoma, were sensitive to significant ethanol-induced disordering within the anesthetically relevant range (100 - 200 mM). Human erythrocytes, cultured fibroblasts and homogenized astroglial cells required higher ethanol concentrations (greater than 250 mM) to produce a similar effect. Intact erythrocytes were approximately twice as sensitive as erythrocyte ghost membranes to ethanol-induced perturbation. The neonatal glial and N2A cells were approximately five times more sensitive than synaptic membranes to ethanol effects. DMPC and DMPC + cholesterol liposomes and myelin membranes were insensitive to ethanol's effects. The incorporation of 10 mole % ganglioside GM1 sensitized the liposomes to ethanol-induced perturbation.
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PMID:On the sensitivity of intact cells to perturbation by ethanol. 261 59

Although it is now well established that the fully interdigitated phase is induced in saturated like-chain phosphatidylcholines (PCs) by a variety of amphipathic molecules including alcohols, no systematic study of the properties of the inducing molecules has been reported. To elucidate the stereochemical features that lead to the alcohol induction of interdigitation in PCs, we have investigated the induction of interdigitation in distearoylphosphatidylcholine (DSPC) by a series of alcohols. Our previously established DPH (1,6-diphenyl-1,3,5-hexatriene) fluorescence intensity method has been expanded (P. Nambi, E. S. Rowe, and T. M. McIntosh (1988), Biochemistry 27:9175-9182) and used to determine which of the alcohols induce interdigitation and to determine the threshold concentrations for each. We have found that each of the n-alcohols up to heptanol and several branched alcohols are capable of inducing interdigitation in DSPC; octanol and nonanol do not appear to induce interdigitation by these criteria. The threshold concentrations for interdigitation for each of these alcohols up to heptanol were found to be correlated with the membrane: buffer partition coefficients. The mole fraction of bound alcohol at the threshold concentration was similar for each of the alcohols up to pentanol. These results are discussed in terms of a general mechanism of the formation of the interdigitated phase.
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PMID:Alcohol induction of interdigitation in distearoylphosphatidylcholine: fluorescence studies of alcohol chain length requirements. 785 25

Large, unilamellar vesicles (LUV) composed of dipalmitoylphosphatidylcholine (DPPC) were made asymmetric in L-alpha-lysopalmitoylphosphatidylcholine (LPC) either by adding a small amount (total mole fraction = 0.003) of LPC to their outer leaflets (LUV-LPCout) or by extracting a small amount from outer leaflets which already contained 0.0015 mol fraction LPC (LUV-LPCin). The slow rate of the transbilayer redistribution of LPC allowed the asymmetric vesicles to be characterized with regard both to their physical properties and to their ability to fuse in the presence of poly(ethylene glycol) (PEG). The fraction of LPC extractable with bovine serum albumin was taken as a measure of LPC transbilayer asymmetry. The ratio of LPC available to that unavailable to BSA extraction was 6 for LUV-LPCout and 0.3 for LUV-LPCin. These asymmetries could not be enhanced significantly by increasing the vesicle LPC content. Measurements of the mixing and leakage of vesicle contents showed that LUV-LPCin fused in the presence of 15% (w/w) PEG without loss of contents but that LUV-LPCout did not fuse in the presence of up to 35% PEG. Vesicles prepared from palmitoyloleoylphosphatidylcholine could also be made asymmetric in LPC, but did not fuse even in the presence of 30% PEG. Quasi-elastic light scattering revealed that LUV-LPCin aggregated at 25 degrees C except when swollen by an osmotic gradient while LUV-LPCout were much less likely to aggregate. Trapped volume determinations suggested that neither type of vesicle was perfectly spherical in shape, but no correlation was found between fusogenicity and vesicle shape. Measurements of the fluorescence properties of TMA-DPH and of C6-NBD-PC suggested that the interface region of the outer leaflet of LUV-LPCin was slightly less ordered and less well packed than that of LUV-LPCout. This slight perturbation of the external vesicle surface correlated with the ability of juxtaposed vesicle bilayers to fuse.
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PMID:A slight asymmetry in the transbilayer distribution of lysophosphatidylcholine alters the surface properties and poly(ethylene glycol)-mediated fusion of dipalmitoylphosphatidylcholine large unilamellar vesicles. 882 98

A large number of pharmaceutically active compounds have a high affinity to acidic phospholipids; good examples are the cationic compounds lidocaine, propranolol, and gentamycin. These drugs influenced the lipid dynamics of liposomes composed of phosphatidylcholine and the acidic phosphatidylglycerol, as judged by the excimer/monomer emission intensity ratio for a pyrene-labeled phospholipid analog, as well as by polarization of DPH fluorescence. When the mole fraction X of PG (XPG) was 0.20, lidocaine increased membrane fluidity. The opposite was true for propranolol, which caused the formation of pyrene lipid-enriched microdomains. Gentamycin had no apparent effect. At XPG = 1.00, all these drugs rigidified membrane. Subsequently, we investigated the detachment of a cationic peripheral membrane protein, cytochrome c (cyt c), by these compounds from liposomes. This was accomplished by monitoring resonance energy transfer from a pyrene-labeled phospholipid to the heme of cyt c. The efficiency of the above compounds to dissociate cyt c varied considerably. In brief, significantly lower concentrations of gentamycin than propranolol or lidocaine were required for half-maximal dissociation of cyt c from liposomes, although the final extent of protein detachment by gentamycin was less complete. ATP augmented the dissociation of cyt c from membranes by lidocaine and propranolol. Stopped-flow measurements also revealed that the half-times differed for the release of cyt c from the membranes. Our results are likely to reflect differences in the contributions of the electrostatic interactions and hydrophobicity to the drug/lipid interaction and comply with two different acidic phospholipid binding sites in cyt c.
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PMID:Detachment of cytochrome c by cationic drugs from membranes containing acidic phospholipids: comparison of lidocaine, propranolol, and gentamycin. 976 16

This article reviews the use of fluorescent lipids and free probes in the studies of lipid regular distribution in model membranes. The first part of this article summarizes the evidence and physical properties for lipid regular distribution in pyrene-labeled phosphatidylcholine (PC)/unlabeled PC binary mixtures as revealed by the fluorescence of pyrene-labeled PC. The original and the extended hexagonal superlattice model are discussed. The second part focuses on the fluorescence studies of sterol regular distributions in membranes. The experimental evidence for sterol superlattice formation obtained from the fluorescent sterol (i.e. dehydroergosterol) and non-sterol fluorescent probes (e.g. DPH and Laurdan) are evaluated. Prospects and concerns are given with regard to the sterol regular distribution. The third part deals briefly with the evidence for polar headgroup superlattices. The emphasis of this article is placed on the new concept that membrane properties and activities, including the activities of surface acting enzymes, drug partitioning, and membrane free volume, are fine-tuned by minute changes in the concentration of bulky lipids (e.g. sterols and pyrene-containing acyl chains) in the vicinities of the critical mole fractions for superlattice formation.
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PMID:Fluorescence studies of lipid regular distribution in membranes. 1209 40

Electric fields, similar in the order of magnitude of the natural membrane fields of cellular lipid/protein membranes, and chemical relaxation spectrometry can be used as tools to quantify the rigidifying effect of cholesterol in membranes. Small unilamellar vesicles of radius a=50+/-3 nm, prepared form phosphatidylcholine, phosphatidylserine and phosphatidyl-glycerol in the molar ratio 1:1:1 and containing the optical lipid probe molecule 2-(3-diphenyl-hexatrienyl) propanoyl)-1-palmitoyl-sn-glycerol-3-phosphocholine (beta-DPH pPC), serve as examples for curved lipid membranes. The data of electrooptical turbidity and absorbance relaxations at the wavelength lambda=365 nm are analysed in terms of membrane bending rigidity kappa and membrane stretching modulus K. Both kappa and K increase with increasing mole fraction x of cholesterol up to x=0.5. The cholesterol induced denser packing of the lipids reduces the extent of both membrane electroporation (ME) and electroelongation of the vesicles. Further on, cholesterol in the lipid phase and sucrose in the aqueous suspension reduce the extent of membrane undulation and electro-stretching.
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PMID:Cholesterol reduces membrane electroporation and electric deformation of small bilayer vesicles. 1592 75

Binary vesicles of cationic lipid dihexadecyldimethylammoniumbromide (DHAB) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were examined by differential scanning calorimetry, fluorescence spectroscopy, and Fourier transform infrared spectroscopy. DHAB/DMPC vesicles demonstrate a complex dependence of the main-transition temperature (T(m)) on their mole proportion of DHAB, with a maximum of 42 degrees C at X(DHAB) = 0.4. An increase of T(m) at X(DHAB) < 0.4 is explained by reorientation of P(-)-N(+) dipoles of the phosphocholine headgroup, resulting in tighter packing of the acyl chains, which increases the thermal energy required for trans --> gauche isomerization. At X(DHAB) > 0.4, Coulombic repulsion between the cationic DHAB headgroups expands the bilayer evident as a decrease in T(m) until a plateau of approximately 28 degrees C at 0.7 < or = X(DHAB) > or = 0.9 is reached, followed by an increment of T(m) to approximately 30 degrees C at X(DHAB) > 0.9. The quenching of DPH-PC fluorescence emission and the decrease in the ratio of peak height intensities of symmetric and antisymmetric -CH(2)- stretching modes suggest an interdigitated phase to form at X(DHAB) > 0.6. Interdigitation allows the membrane to accommodate the augmented Coulombic repulsion between DHAB headgroups because of increasing cationic surface charge density while simultaneously causing tighter packing of the acyl chains evident first as a plateau at 0.7 < or = X(DHAB) > or = 0.9 and subsequently as an increase in T(m) at X(DHAB) > 0.9. Screening of the membrane charges by NaCl abolishes the quenching of DPH emission and decreases T(m), thus revealing electrostatic repulsion as the driving force for interdigitation.
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PMID:Increasing surface charge density induces interdigitation in vesicles of cationic amphiphile and phosphatidylcholine. 1595 13

Seventeen different, chemically defined phosphatidylcholines, dispersed in aqueous medium in the form of large unilamellar vesicles, have been tested for solubilization by the non-ionic detergent Triton X-100. The temperatures (either 20 degrees C or 45 degrees C) were such that the bilayers were always in the liquid-disordered state. For each case, the solubilization parameters, Don (total detergent: lipid mole ratio producing the onset of solubilization) and D50 (total detergent: lipid mole ratio producing 50% solubilization), were determined under equilibrium conditions. Both parameters varied generally in parallel. When double bonds were introduced to the acyl chains, other factors remaining constant, solubilization became more difficult, i.e., more detergent was required. Cis-unsaturated phospholipids required more detergent than the corresponding trans-isomers. Increasing chain length in saturated phospholipids between C12 and C16 decreased moderately the detergent/lipid ratios causing solubilization. Acyl and alkyl phospholipids were equally susceptible to Triton X-100 solubilization. Lipid chain order, as measured by DPH fluorescence polarization, seemed to facilitate solubilization, perhaps because more ordered bilayers have a smaller capacity to accommodate detergent monomers without breaking down into lipid-detergent mixed micelles.
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PMID:Detergent solubilization of phosphatidylcholine bilayers in the fluid state: influence of the acyl chain structure. 1657 63

The surface area occupied by nonionic detergents of the type C(12)EO(n) (n = 1-8) in POPC C (12)EO (n) mixed membranes was studied by means of time-resolved resonance energy transfer (RET) between the fluorescent probe molecules NBD-PE and rhodamine-PE. The area data were interpreted within the frame of Israelachvili's concept of packing constraints yielding the critical packing parameter, f, as a measure of the asymmetry of the molecular shape of the membrane constituents. The asymmetry of the molecular shape of the detergent increases with the ethylene oxide chain length and correlates with the potency of the detergent to solubilize the bilayers and the reduction of the DPH order parameter. For n = 1-3, the membrane surface was found to expand by 0.25-0.30 nm(2) per incorporated C(12)EO(n) molecule. This value corresponds to the cross section of one hydrocarbon chain in liquid-crystalline phases. On increasing n from n = 4 to n = 8 the net area per detergent molecule increases from 0.43 nm(2) to 1.16 nm(2). These surface requirements are consistent with a disordered, coiled conformation of the EO-chains hydrated with up to two water molecules per ethylene oxide unit. For n > 5 the limiting mole fraction of the bilayer saturation was deduced from the f-data in the two-component bilayer. DPH and NBD-PE fluorescence lifetime data are discussed to give an indication of the accessibility of the probe environment to water molecules.
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PMID:Surface areas and packing constraints in POPC C (12)EO (n) membranes. A time-resolved fluorescence study. 1702 59


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