1-2-oleoylphosphatidylcholine and parinaric-acid

Cell membranes have a nonhomogenous lateral organization. Most information about such nonhomogenous mixing has been obtained from model membrane studies where defined lipid mixtures have been characterized. Various experimental approaches have been used to determine binary and ternary phase diagrams for systems under equilibrium conditions. Such phase diagrams are the most useful tools for understanding the lateral organization in cellular membranes. Here we have used the fluorescence properties of trans-parinaric acid (tPA) for phase diagram determination. The fluorescence intensity, anisotropy, and fluorescence lifetimes of tPA were measured in bilayers composed of one to three lipid components. All of these parameters could be used to determine the presence of liquid-ordered and gel phases in the samples. However, the clearest information about the phase state of the lipid bilayers was obtained from the fluorescence lifetimes of tPA. This is due to the fact that an intermediate-length lifetime was found in samples that contain a liquid-ordered phase and a long lifetime was found in samples that contained a gel phase, whereas tPA in the liquid-disordered phase has a markedly shorter fluorescence lifetime. On the basis of the measured fluorescence parameters, a phase diagram for the 1,2-dioleoyl-sn-glycero-3-phosphocholine/N-palmitoyl sphingomyelin/cholesterol system at 23 °C was prepared with a 5 mol % resolution. We conclude that tPA is a good fluorophore for probing the phase behavior of complex lipid mixtures, especially because multilamellar vesicles can be used. The determined phase diagram shows a clear resemblance to the microscopically determined phase diagram for the same system. However, there are also significant differences that likely are due to tPA's sensitivity to the presence of submicroscopic liquid-ordered and gel phase domains.

Topics: Anisotropy; Cholesterol; Fatty Acids, Unsaturated; Fluorescence; Phosphatidylcholines; Sphingomyelins; Surface Properties

Topics: Antioxidants; Azo Compounds; beta Carotene; Carotenoids; Chromatography, High Pressure Liquid; Fatty Acids, Unsaturated; Fluorescent Dyes; Indicators and Reagents; Kinetics; Liposomes; Luminescent Measurements; Oxygen Consumption; Phosphatidylcholines; Spectrometry, Fluorescence; Ubiquinone; Vitamin E

The diversity and distribution of gangliosides in vertebrate tissue suggests an important role in cellular recognition. Two types of experiments are reported to test the hypothesis that gangliosides can congregate to form an adhesive junction between two membranes. First, to monitor ganglioside distribution and mobility in different regions of two large spherical bilayer membranes, fluorescent derivatives of natural gangliosides were synthesized. Second, the cation carrier nonactin was used as a conductance probe to measure the membrane surface potential, which would be altered if there were a redistribution of the charged gangliosides. These studies were conducted in large spherical artificial membranes made from egg phosphatidylcholine or oleoylpalmitoylphosphatidylcholine with 0-12 mol % bovine brain gangliosides dissolved in n-decane. The fluorescent gangliosides utilized were lucifer yellow adducts to the sialic acids (LY-gangliosides) or a cis-paranaric acid substitution of the N-acyl moiety in the ceramide portion of gangliosides GM1 and GD1a (paranaryl-GM1 and paranaryl-GD1a). The polarized fluorescence from the adhesive junction between two membranes containing LY-gangliosides or either paranarylganglioside was compared to that in nonadhesive regions. For LY-gangliosides, total fluorescence in the junction decreased with time, possibly due to electrostatic repulsion of this highly charged derivative. For paranarylgangliosides, fluorescence in the junction increased 7-fold with time, suggesting congregation of this ganglioside. In both cases, a measure of rotational mobility, fluorescence anisotropy, increased dramatically, about 2-fold, as expected for restricted mobility of adhesive compounds. Independent evidence for congregation of charge-bearing gangliosides was found with the conductance probe nonactin.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adhesiveness; Anti-Bacterial Agents; Electrochemistry; Fatty Acids, Unsaturated; Fluorescence Polarization; Fluorescent Dyes; Gangliosides; Isoquinolines; Lipid Bilayers; Macrolides; Membrane Potentials; Membranes, Artificial; Phosphatidylcholines

An analysis is presented of the complex anisotropy behavior of trans-parinaric acid in single component DEPC lipid bilayers. It is shown that a model involving two species with distinct lifetime and motional behavior is required, and is adequate, to explain the observed data. In particular, the observed increase in the anisotropy at long times demonstrates the presence of a species with a long fluorescence lifetime that has a high anisotropy. The time dependence of the anisotropy for these two environments is treated using both a purely mathematical sum of exponentials and a constrained fit based on an approximate solution of the anisotropic diffusion problem. In this latter model the anisotropy is described in terms of the second and fourth rank order parameters, (P2) and (P4), and a single dynamical parameter, D1, the perpendicular diffusion coefficient for this uniaxial probe. The parameters of both models are accurately determined from the fits to the data when two environments coexist and an association is made between lifetime components and distinct rotational sites. The values of the parameters obtained demonstrate the "solid-like" and "fluidlike" nature of these two coexisting environments.

Topics: Fatty Acids, Unsaturated; Fluorescent Dyes; Lipid Bilayers; Mathematics; Models, Theoretical; Phosphatidylcholines; Spectrometry, Fluorescence; Thermodynamics