dipalmitoylphosphatidylserine and 1-2-dipalmitoyl-3-phosphatidylethanolamine

The studies on the influence of cholesterol on phospholipids accumulated in inner leaflet of membrane are performed rather rarely, especially in the presence of electrolytes, which are present in membrane environment. Therefore, in this work the interactions between cholesterol and saturated phosphatidylethanolamine (PE) and phosphatidylserine (PS) were studied in binary (phospholipid/cholesterol) and ternary (PS/PE/cholesterol) monolayers in the presence and absence of sodium and calcium ions. The composition of ternary films was estimated to reflect the proportion of PSs to PEs in inner layer of human erythrocyte membrane. The influence of electrolytes on pure PS and PE films was also analyzed. It was found that both sodium and calcium ions affect the condensation of DPPS films, and influence the interactions in DPPS/cholesterol monolayers. On the other hand, no effect of these ions on DPPE films as well as on DPPE/cholesterol interactions in the mixed systems was observed. The results obtained for ternary mixtures prove that in the presence of Na(+) the interactions between the lipids are more favorable than in the absence of these ions. This is in contrast to the effect of Ca(2+). All the results were thoroughly analyzed in the context of the structure of polar heads of the investigated phospholipids.

Topics: Calcium; Cholesterol; Erythrocyte Membrane; Humans; Ions; Phase Transition; Phosphatidylethanolamines; Phosphatidylserines; Phospholipids; Pressure; Sodium; Surface Properties; Temperature; Water

The interaction between dimethylsulfoxide (DMSO) and phospholipid monolayers with different polar headgroups was studied using "in situ" Brewster angle microscopy (BAM) coupled to a Langmuir trough. For a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer, DMSO was shown to significantly impact the structure of the liquid expanded (LE) and gaseous phases. The domains reorganized to much larger domain structures. Domains in the liquid condensed (LC) phase were formed on the DMSO-containing subphase at the mean molecular area where only gaseous and LE phases were previously observed on the pure water subphase. These results clearly demonstrate the condensing and caging effect of DMSO molecules on the DPPC monolayer. Similar effects were found on dipalmitoyl phosphatidyl ethanolamine, glycerol, and serine phospholipids, indicating that the condensing and caging effect is not dependent upon the phospholipid headgroup structure. The DMSO-induced condensing and caging effect is the molecular mechanism that may account for the enhanced permeability of membranes upon exposure to DMSO.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Cell Membrane; Dimethyl Sulfoxide; Glycerophospholipids; Microscopy; Phosphatidylethanolamines; Phosphatidylglycerols; Phosphatidylserines

Pure 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine (DPPC) or mixed DPPC:1,2-dipalmitoyl phosphatidyletanolamine (DPPE):1,2-dipalmitoyl diphosphatidylserine (DPPS) (17:5:3) liposomes were incorporated with 5 mol% dietary carotenoids (beta-carotene, lutein and zeaxanthin) or with cholesterol (16 and 48 mol%) in the absence or presence of 15 mol% carotenoids, respectively. The carotenoid incorporation yields ranged from 0.42 in pure to 0.72 in mixed phospholipid liposomes. They decreased significantly, from 3 to 14%, in the corresponding cholesterol-doped liposomes, respectively. Highest incorporation yields were achieved by zeaxanthin and lutein in phospholipid liposomes while in cholesterol-containing liposomes, lutein was highest incorporated. The effects on membrane structure and dynamics were determined by differential scanning calorimetry, steady-state fluorescence and anisotropy measurements. Polar carotenoids and cholesterol cause similar, dose-dependent effects: ordering and rigidification revealed by broadening of the transition peak, and increase of anisotropy. Membrane hydrophobicity is determined by cholesterol content and carotenoid polarity. In cholesterol-doped liposomes, beta-carotene is less incorporated than in cholesterol-free liposomes. Our observations suggest effects of carotenoids, even at much lower effective concentrations than cholesterol (8 to 80-fold), on membrane structure and dynamics. Although they are minor constituents of animal membranes, carotenoids may act as modulators of membrane phase transition, fluidity, polarity and permeability, and therefore, can influence the membrane physiology and pathology.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Calorimetry, Differential Scanning; Carotenoids; Cholesterol; Fluorescence Polarization; In Vitro Techniques; Liposomes; Membrane Fluidity; Phosphatidylethanolamines; Phosphatidylserines; Thermodynamics

We have recently shown that C5b-6 binds to the erythrocyte membrane via an ionic interaction with sialic acid before the addition of C7 and subsequent membrane insertion. In this study we assessed the role of anionic lipids in the binding of the terminal complement proteins to the membrane and the efficiency of subsequent hemolysis. Human erythrocytes were modified by insertion of dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylserine (DPPS), dipalmitoyl phosphatidylethanolamine (DPPE), or dipalmitoyl phosphatidic acid (DPPA). Lipid incorporation and the hemolytic assays were done in the presence of 100 micromol/L sodium orthovanadate to prevent enzymatic redistribution of lipid. We found that the neutral lipids, DPPC and DPPE, did not affect C5b-7 uptake or hemolysis by C5b-9. In contrast, the two acidic phospholipids, DPPS and DPPA, caused a dose-dependent increase in both lysis and C5b-7 uptake. We conclude that the presence of anionic lipids on the exterior face of the membrane increases C5b-7 uptake and subsequent hemolysis. It is known that sickle cell erythrocytes have increased exposure of phosphatidylserine on their external face and are abnormally sensitive to lysis by C5b-9. The data presented here provide a plausible mechanism for this increased sensitivity.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Anions; Carbon Radioisotopes; Complement C5; Complement Pathway, Alternative; Erythrocyte Membrane; Fluorescent Dyes; Hemolysis; Humans; Membrane Lipids; Phosphatidic Acids; Phosphatidylethanolamines; Phosphatidylserines; Phospholipids

To determine the nonideal mixing of two lipid components within the membrane, lipid cross-linking experiments were carried out on dipalmitoylphosphatidylethanolamine (DPPE) vesicles and on dipalmitoylphosphatidylethanolamine/dipalmitoylphosphatidylserine (DPPE/DPPS) vesicles. By comparison of the cross-linking reactions on both types of vesicle the mean neighbourhood relations within the binary lipid mixture can be obtained. To elucidate the relationship between cluster formation and phase transition, the temperature dependences of the lipid arrangement within the vesicle membrane and of the lipid order parameter describing the fluidity of the membrane were measured. Cluster size and phase transition correlate: during the phase transition of the lipid species with the lower phase-transition temperature (DPPS) the nonideality of the mixture increases by phase separation. Above the phase transition temperature of the second lipid species (DPPE) the clusters disappear and a slight alternating lipid arrangement is characteristic of the fluid phase.

Topics: Chemical Phenomena; Chemistry; Lipid Bilayers; Mathematics; Microscopy, Electron; Models, Biological; Molecular Conformation; Phosphatidylethanolamines; Phosphatidylserines