Temperature-induced changes in lipid composition and transition temperature of flight muscle mitochondria of Schistocerca gregaria

The lipid composition of flight muscle mitochondria was determined in adult male $\text{Schistocerca gregaria}$ acclimated for 30 days at 31°C and 45°C respectively. Locusts held at 31°C showed lower levels of phosphatidylcholine and higher levels of phosphatidylethanolamine than the 45°C-acclimated insects. A trend towards an increased cholesterol:phospholipid ratio was also observed at the higher temperature. Wide angle X-ray diffraction procedures indicated a difference of 5°C in the lipid phase transition temperatures of mitochondrial preparations derived from the two groups of insects with the 45°C-acclimated samples demonstrating the higher transition temperature.     

Comparative study on the properties of saturated phosphatidylethanolamine and phosphatidylcholine bilayers: Barrier characteristics and susceptibility to phospholipase A2 degradation

Comparative studies on bilayer systems of saturated phosphatidylcholines and phosphatidylethanolamines revealed a maximum in ionic permeability in phosphatidylcholine bilayers at the temperature of the gel to liquid-crystalline phase transition but such an increase in permeability was not detectable in bilayers of phosphatidylethanolamine. Furthermore, it was found that at the phase transition temperature the phosphatidylcholine bilayers are subject to rapid hydrolysis by pancreatic phospholipase A₂ whereas phosphatidylethanolamine bilayers are not. These differences are discussed in view of detailed information on the molecular organization in the gel and liquid crystalline phases of the two phospholipid classes.     

Effects of acclimation temperature on membrane phospholipids in the flesh fly Sarcophaga similis

Cold acclimation is a well‐known strategy for enhancing cold tolerance in ectotherms including insects. Nevertheless, information on the physiological mechanisms underpinning this phenomenon is still limited. Biological membrane integrity is critical for insects to perform at low temperatures, and an advantage is conferred on those insects that can adjust the composition of their membrane phospholipids. Such changes contribute to homeoviscous adaptation, a process that allows membranes to maintain a liquid–crystalline (fluid) state at low temperatures. Here we investigated phospholipids in the flesh fly Sarcophaga similis acclimated to various temperatures. Significant differences were observed in the composition of their fatty acyl chains: flies acclimated to low temperatures showed a higher proportion of palmitic and oleic acids at the expense of palmitoleic acid. Other fatty acids (stearic, linoleic, linolenic, arachidonic, eicosapentaenoic acids) were not significantly changed. The degree of unsaturation decreased in cold‐acclimated flies, but the difference was quite small. The weighted average chain length and number of double bonds were unchanged among flies acclimated to different temperatures. As temperatures decreased, the percentage of phosphatidylethanolamine increased to twice that of phosphatidylcholine. We discuss the role of these phospholipid changes in cold acclimation.     

Effect of environmental temperature on the phase properties and lipid composition of flight muscle mitochondria of Schistocerca gregaria

The phase properties and composition of flight muscle mitochondrial membranes were determined in adult male Schistocerca gregaria, acclimated for one month at 31°C and 45°C. Wide angle X-ray diffraction procedures demonstrated a difference of 5°C in the lipid phase trasition temperatures of whole mitochondrial membrane preparations from the two groups of insects; the higher transition temperature was recorded for insects acclimated at 45°C. No statistically significant differences were observed in the ratios of protein:lipid, protein:phospholipid and cholesterol:phospholipid between mitochondria from 31°C- and 45°C-acclimated insects. Elevated temperature also resulted in depressed levels of phosphatidylethanolamine and increased levels of phosphatidylcholine with other phospholipid species remaining unchanged. No differences were observed in the fatty acid composition of the total phospholipid extract.     

Alamethicin-induced changes in lipid bilayer morphology

We have found that alamethicin, in the absence of an electric field, modifies both the hydrophilic surface and hydrophobic core of lipid bilayers. As shown by freeze-fracture and X-ray diffraction experiments with multiwalled vesicles, alamethicin increases the fluid space between bilayers by as much as 50 nm, and at the same time perturbs the hydrocarbon regions of the bilayers. For suspensions of gel-state lipid treated with alamethicin, uniformly spaced rows of particles cover the fracture faces and corresponding linear arrays of stain-collecting depressions cover the hydrophilic surfaces. In the liquid-crystalline state, alamethicin induces an irregular granular texture on the fracture faces.     

Effect of environmental temperature on the phospholipid metabolism of gill mitochondria of Carcinus maenas

The different types of phospholipids extracted from gill mitochondria of crab Carcinus maenas have been analysed and it was found that a significant increase of the phosphatidylethanolamine (PE) content and a concomitant decrease of the phosphatidylcholine (PC) amount are present in animals living in low temperatures. The incorporation of [³H]ethanolamine in total phospholipids, PE and PC, was demonstrated in gill mitochondria and a thermal alteration of the in vivo exchange of PE between mitochondria and 10,000 g supernatant is suggested by the kinetics of the incorporation. It is suggested that the conversion of PE to PC by N-methylation is very low in crab gills. There is a marked action of acclimation temperature on the gills-hemolymph exchange of PC and PE. It is postulated that the changes reported at the level of the PE → PC conversion by N-methylation and in phospholipid exchange between hemolymph and gills could be implicated in adapting the organism to seasonal fluctuations of environmental temperatures.     

The nature of lipidic particles and their roles polymorphic transitions

The structural transition between bilayer (L_α), inverted hexagonal (H_II and inverted cubic (C_II) phases in mixtures of unsaturated phosphatidylethanolamines (PE) and phosphatidylcholines (PC) were investigated. Freeze fracture electron micrographs of intermediate stages of phase transitions showed that C_II was a stable intermediate form between the L_α-H_II transition. The electron microscopic observation was supported by X-ray diffraction and ³¹P-NMR results. Detailed morphology revealed that during the L_α-C_II transition, interlamellae attachment points (conical lipidic particles) connect adjacent bilayers to form arrays of entrapped water pockets (inverted micelles). These water-containg spherical units were packed in a cubic lattice. In the C_II to H_II transition, these spherical units were linearly connected to form tubes. During the L_α-H_II transition, a ripple pattern was observed across the otherwise smooth lamellar. The troughs of the ripples were transformed into linear connections between adjacent bilayers, thereby converting multilayer structures into parallel tubes. No lipidic particles were involved in this type of transition. We show that there are different mechanisms involved in the L_α, H_II, C_II polymorphic transitions, and that different types of ‘lipidic particles’ representing different molecular organizations may be involved in each case. Models of these transitions are proposed.     

Raman spectroscopic and X-ray diffraction studies of the effect of temperature and Ca2+ on phosphatidylethanolamine dispersions

Raman spectroscopy and X-ray diffraction are used to study the effect of heat and Ca²⁺ on dimyristoylphosphatidylethanolamine dispersions. Unlike phosphatidylcholine dispersions, dimyristoylphosphatidylethanolamine bilayers (at pH 8) require heating above T_m in order for hydration to occur and apparently bind Ca²⁺ at very low levels. These results are related to models for membrane fusion.     

Effect of lipid composition on buforin II structure and membrane entry

Buforin II is a 21-amino acid polycationic antimicrobial peptide derived from a peptide originally isolated from the stomach tissue of the Asian toad Bufo bufo gargarizans. It is hypothesized to target a wide range of bacteria by translocating into cells without membrane permeabilization and binding to nucleic acids. Previous research found that the structure and membrane interactions of buforin II are related to lipid composition. In this study, we used molecular dynamics (MD) simulations along with lipid vesicle experiments to gain insight into how buforin II interacts differently with phosphatidylcholine (PC), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE) lipids. Fluorescent spectroscopic measurements agreed with the previous assertion that buforin II does not interact with pure PC vesicles. Nonetheless, the reduced entry of the peptide into anionic PG membranes versus neutral PC membranes during simulations correlates with the experimentally observed reduction in BF2 translocation through pure PG membranes. Simulations showing membrane entry into PC also provide insight into how buforin II may initially penetrate cell membranes. Our MD simulations also allowed us to consider how neutral PE lipids affect the peptide differently than PC. In particular, the peptide had a more helical secondary structure in simulations with PE lipids. A change in structure was also apparent in circular dichroism measurements. PE also reduced membrane entry in simulations, which correlates with decreased translocation in the presence of PE observed in previous studies. Together, these results provide molecular-level insight into how lipid composition can affect buforin II structure and function and will be useful in efforts to design peptides with desired antimicrobial and cell-penetrating properties.     

Effects of temperature on properties of flight neurons in the locust

High ambient temperatures increase the wing-beat frequency in flying locusts, Locusta migratoria. We investigated parameters of circuit and cellular properties of flight motoneurons at temperatures permissive for flight (20–40 °C). As the thoracic temperature increased motoneuronal conduction velocity increased from an average of 4.40 m/s at 25 °C to 6.73 m/s at 35 °C, and the membrane time constant decreased from 11.45 ms to 7.52 ms. These property changes may increase locust wing-beat frequency by affecting the temporal summation of inputs to flight neurons in the central circuitry. Increases in thoracic temperature from 25–35 °C also resulted in a hyperpolarization of the resting membrane potentials of flight motoneurons from an average of-41.1 mV to -47.5 mV, and a decrease of input resistances from an average of 3.45 M to 2.00 M. Temperature affected the measured input resistance both by affecting membrane properties, and by altering synaptic input. We suggest that the increase in conduction velocity Q₁₀=1.53) and the decrease of membrane time constant (Q₁₀=0.62) would more than account for the wing-beat frequency increase (Q₁₀=1.15). Hyperpolarization of the resting membrane potential (Q₁₀=1.18) and reduction in input resistance (Q₁₀=0.54) may be involved in automatic compensation of temperature effects.Abbreviations ANOVA analysis of variance - CPG central pattern generator - DL dorsal longitudinal muscles - EMG electromyographic - MN motoneuron - PSP post synaptic potential - Q₁₀ temperature coefficient - RMP resting membrane potential - S.D. standard deviation - SR stretch receptor     

The interfacial tension of the lipid membrane formed from lipid-cholesterol and lipid-lipid systems

Interfacial tension has been determined for phosphatidylcholine-cholesterol, phosphatidylcholine-phosphatidylethanolamine, and phosphatidylethanolamine-cholesterol membranes. Phosphatidylcholine (PC), phosphatidylethanolamine (PE), and cholesterol (Ch) were to be investigated, because of their presence in biological membranes. Interfacial tension values of pure components are 0.81×10⁻³ N/m, 1.67×10⁻³ N/m, and 2.36×10⁻³ N/m, respectively. The 1∶1 complexes were formed during formation of the PC-Ch, PC-PE, and PE-Ch lipid membranes. The following parameters describing the complexes were determined: A ₃ ⁻¹ , the surface concentrations of the lipid membranes formed from these complexes; γ₃, the interfacial tensions of such membranes and K, the stability constants of these complexes.     

Effect of α-tocopherol on the phase transition of phosphatidylcholine and on water transport through phosphatidylcholine liposome membranes

The interaction between α-tocopherol and phosphatidylcholine was studied in liposomes by differential scanning calorimetry and osmotic water transport studies. Addition of α-tocopherol to phosphatidylcholine resulted in a reduction in enthalpy at the transition temperature, a rise in osmotic water permeability of the liposomes below the phase transition temperature and disappearance of the discontinuity of osmotic water transport at the phase transition. Also the temperature dependence of osmotic water transport was reduced below the transition temperature. A comparison between cholesterol and α-tocopherol in regulation of permeability was made and the physiological relevance of tocopherol in regulation of membrane permeability is discussed.     

Lipid composition of pine needle chloroplasts and apple bark tissue as affected by growth temperature and daylength changes. 1. Phospholipids

Phospholipid (PL) and fatty acid composition of chloroplasts of pine needles ( Pinus sylvestris L.) and apple bark tissue ( Malus sylvestris Mill. cv. Golden Delicious) was determined in a series of experiments in which growth temperature and daylength were changed. Trees were exposed to 0 and 20°C and to daylength conditions of 9 and 14 h. All 16 possible combinations were investigated by transfer of the trees from the original condition to each of the other conditions. There was no direct relation between cold hardiness and PL composition in apple bark and pine chloroplasts, when temperature and/or daylength were changed. PL composition seemed to be strongly determined by the sequence of the imposed sets of daylength and temperature. The effect of these environmental factors on PL composition strongly differed from that for cold hardiness. The correlation between the levels of PL (and phosphatidylcholine) and cold hardiness, as reported in the literature, was also evident in this experiment, when treatments, presenting the normal seasonal order, were compared. It seems that the yearly cycle of temperature and daylength is important in determining the PL composition of apple bark and pine chloroplasts.     

An X-ray diffraction study on phase transition temperatures of various membranes isolated from Tetrahymena pyriformis cells grown at different temperatures

Mitochondrial, microsomal and pellicular membranes were isolated from Tetrahymena cells grown at 39°C or 15°C, and phospholipids, in turn, were separated from total lipids extracted from these membranes. The effect of growth temperature on their solid-to-fluid phase transition temperature was examined by wide-angle X-ray diffraction. The transition temperatures of phospholipids from mitochondria, microsomes and pellicles were 21, 19 and 26°C for cells grown at 39°C and ?8, ?3 and 6°C for cells grown at 15°C, respectively. All phospholipids were found in a completely fluid state at these growth temperatures. From a comparison between the phospholipids and total lipids from pellicles of cells grown at 39°C, a triterpenoid alcohol, tetrahymanol, caused the transition temperature to increase. The alignment of tetrahymanol in membranes was examined with pellicle's total lipid oriented in a sample holder.     

Regulation of lipid droplet size and phospholipid composition by stearoyl-CoA desaturase

Fatty acid desaturation regulates membrane function and fat storage in animals. To determine the contribution of stearoyl-CoA desaturase (SCD) activity on fat storage and development in the nematode Caenorhabditis elegans, we analyzed the lipid composition and lipid droplet size in the fat-6;fat-7 desaturase mutants independently and in combination with mutants disrupted in conserved lipid metabolic pathways. C. elegans with impaired SCD activity displayed both reduced fat stores and decreased lipid droplet size. Mutants in the daf-2 (insulin-like growth factor receptor), rsks-1 (homolog of p70S6kinase, an effector of the target of rapamycin signaling pathway), and daf-7 (transforming growth factor β) displayed high fat stores, the opposite of the low fat observed in the fat-6;fat-7 desaturase mutants. The metabolic mutants in combination with fat-6;fat-7 displayed low fat stores, with the exception of the daf-2;fat-6;fat-7 triple mutants, which had increased de novo fatty acid synthesis and wild-type levels of fat stores. Notably, SCD activity is required for the formation of large-sized lipid droplets in all mutant backgrounds, as well as for normal ratios of phosphatidylcholine (PC) to phosphatidylethanolamine (PE). These studies reveal previously uncharacterized roles for SCD in the regulation of lipid droplet size and membrane phospholipid composition.     

Cubic topology in surfactant and lipid mixtures

Ternary systems of palmitoyl-oleoyl-phosphatidylcholine (POPC) and the non-ionic surfactant C₁₂EO₂ (di-ethylene-oxide-mono-dodecyl-ether) in water have been studied with optical microscopy, NMR, DSC and X-rays from ambient temperatures to 45 °C. Below 29 °C the system is in the lamellar liquid crystalline state. Between 30 and 32 °C it transforms into a cubic Ia3d structure which converts into the cubic Pn3m phase at 39 °C. The transitions are fully reversible. An epitaxial relationship between all three phases was found, which is an elegant and convenient way to rearrange molecules from lamellar bilayers to a network of curved surfaces. The la3d (Q²³⁰) to Pn3m (Q²²⁴) transition occurs without measurable enthalpy change. This, together with the metric relation of 1.60 between the cubic lattice constants is strong evidence for a Bonnet transformation, where the structural changes occur without change in curvature. The potential significance of the cubic phases as intermediate structures for biological processes, e. g. transport across a bilayer or fusion of membranes, are discussed.     

Adaptive changes in lipid composition of rat liver plasma membrane during postnatal development following maternal ethanol ingestion

The fatty acid composition of constituent phospholipids and the cholesterol content of rat liver plasma membranes were determined subsequent to maternal alcohol ingestion during pregnancy and lactation. The alcoholic group was given a liquid Metrecal diet containing 37% ethanol-derived calories. The control group was pair-fed an isocaloric sucrose/Metrecal diet. Litters were killed for lipid analyses at days 5, 15 and 25 after birth. These studies revealed that the total phospholipid phosphorus was similar and increased significantly with age in both groups. Cholesterol also increased significantly with age in both groups but was greater in the alcoholic pups, resulting in a higher cholesterol/phospholipid molar ratio. While the phosphatidylethanolamine (PE) content increased with age in both groups, that of sphingomyelin decreased. Phosphatidylserine + phosphatidylinositol (PS + PI) was significantly higher in the control group at all ages studied. A consistent increase of C22:6 in phosphatidylcholine (PC), sphingomyelin, PS + PI and in the total phospholipid fraction from alcoholic pups was observed. Although other fatty acid changes were found in PC, PS + PI and sphingomyelin, PE was not affected. These results suggest that specific adaptive changes were induced in the liver plasma membrane lipids of the progeny from alcoholic rats.     

Polymorphic phase behaviour of dilinoleoylphosphatidylethanolamine and palmitoyloleoylphosphatidylcholine mixtures: Structural changes between hexagonal,cubic and bilayer phases

The polymorphic phase behaviour of dilinoleoylphosphatidyethanolamine (DLPE) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) is investigated by freeze-fracture electron microscopy, X-ray diffraction and ³¹P-NMR. The structures at 5% or less POPC are predominantly inverted hexagonal (H_II), whereas at 15% or more POPC, the structure is mostly bilayer (L), interrupted by defects (lipidic particles). A cubic phase structure is observed in the transition range between H and L phases; the cubic arrangement deteriorates at higher temperatures into an amorphous aggregate of spherical units. Both cubic and amorphous structures contribute to the isotropic ³¹P resonance, with no preference for PC or PE partitioning in the isotropic motion as observed by high resolution NMR. The existence of the cubic phase seems to depend critially on the homogeneity and the degree unsaturation of the phospholipids.