Peculiarities of the phospholipid and fatty acid composition of erythrocyte plasma membranes of the Black Sea fish

The phospholipid and the fatty acid composition of the main phospholipids families of erythrocyte plasma membranes was studied in two species of cartilaginous fish: the common thrasher (Raja clavata L.) and the common stingray (Dasyatis pastinaca) and three bony fish species: the scorpion fish (Scorpaena porcus L.), the smarida (Spicara flexuosa Raf.), and the horse mackerel (Trachurus mediterraneus ponticus Aleev). It was shown that in the studied fish, 70.0-80.0 % of all membrane phospholipids were composed of phosphatidylcholine and phosphatidylethanolamine. Phosphatidylserine, monophosphoinositide, and sphingomyelin were minor components whose content in the erythrocyte membrane fluctuated from 3.0 % to 13.0 %. The fatty acid phospholipids composition was represented by a large specter of acids. From saturated acids, basic for plasma membranes are palmitic (C16: 0) and stearic (C18: 0) acids. From unsaturated acids, the larger part belong to mono-, tetra-, penta-, and hexaenoic acids in fish phospholipids. The calculation of the double bond index and of the unsaturation coefficient showed difference in the deformation ability of erythrocyte membranes of the studied fish.     

Changes in lipid composition of hepatocyte plasma membrane induced by overfeeding in duck

This experiment was carried out to examine the influence of overfeeding ducks with corn on the lipid composition of hepatocyte plasma membrane. Seventy-day-old male Mule ducks (Cairina moschata × Anas platyrhynchos) were overfed with corn for 12.5 days in order to induce fatty livers. The cholesterol and phospholipid contents were approximately 50% higher in hepatocyte plasma membranes from fatty livers compared to those of lean livers obtained from non-overfed ducks. However, the cholesterol/phospholipids molar ratio did not differ between both groups. Overfeeding induced a significant change in phospholipid composition of hepatocyte plasma membrane with a decrease in phosphatidylcholine proportion and conversely an increase in phosphatidylethanolamine. The fatty acid profile of phospholipids was also altered. In fatty hepatocyte plasma membrane, the overall proportion of polyunsaturated fatty acids (PUFA) was decreased and this was due to the decrease of some of, but not all, the PUFA. In addition, the proportions of oleic acid and n-9 series unsaturated fatty acids were higher in fatty than in lean liver membranes. This study provides evidence that overfeeding with a carbohydrate-rich corn-based diet induces a de novo hepatic lipogenesis in Mule duck which predominates over dietary lipid intake to change the lipid composition of the hepatocyte plasma membrane.     

Effect of alterations in membrane lipid unsaturation on the properties of the insulin receptor of Ehrlich ascites cells

We have altered the phospholipid composition of the plasma membranes of Ehrlich ascites cells grown in mice and studied the effects on the properties of the insulin receptor of this cell. The insulin receptor of the Ehrlich cell demonstrated all of the binding characteristics of mammalian insulin receptors: specificity for insulin and insulin analogs, saturability, inverse relationship of steady-state binding levels to temperature, and negative cooperativity. Cellular phospholipids enriched in monounsaturated fatty acyl groups were produced by growth in animals that were maintained on a diet rich in coconut oil; cellular phospholipids enriched in polyunsaturated fatty acyl groups were produced in animals fed sunflower oil. Insulin receptors were present in the normal cells at 180 000 sites/cell but this fell to 125 000 (p <0.001) in cells enriched in monounsaturated fatty acids and rose to 386 000 (p <0.001) in cells enriched in polyunsaturated fatty acids. The normal cells had affinity constants ( and ) of 0.03 and 0.01 nM⁻¹. The cells enriched in monounsaturated fatty acids had an increase in these affinity constants to 0.06 and 0.03 nM⁻¹ whereas values of 0.01 and 0.005 nM⁻¹ were obtained in the cells enriched in polyunsaturated fatty acids (all comparison p <0.001). Thus, increased unsaturation of plasma membrane phospholipids, produced by dietary manipulations, was associated with an increase in insulin receptor number but a decrease in binding affinity. In contrast, increased saturation of the phospholipids of the plasma membrane was associated with a decrease in receptor number and an increase in affinity. The results can be explained by a model in which the insulin receptor is assumed to be multimeric.     

Effect of temperature acclimatization on the fatty acid composition of goldfish intestinal lipids

1. The fatty acid composition of whole goldfish, whole-intestinal mucosa, intestinal mucosal membranes and individual phospholipids extracted from mucosal membranes were measured, fish adapted to different temperatures being used. 2. Alterations of the adaptation temperature did not noticeably affect the fatty acid composition of the whole-fish lipids, but there were marked changes in the fatty acids of lipids extracted from homogenates of goldfish intestinal mucosa. These changes were more pronounced in a membrane fraction prepared from these homogenates. Raising the adaptation temperature by 20 degrees C halved the percentage of C(20:1), C(20:4) and C(22:6) fatty acids and nearly doubled the percentage of C(18:0) and C(20:3) fatty acids recovered. 3. Choline phosphoglycerides constituted about one-half and ethanolamine phosphoglycerides about one-quarter of the total membrane phospholipids. 4. The fatty acids of choline and ethanolamine phosphoglycerides were more susceptible to temperature-dependent changes than were the phosphoglycerides of inositol or serine. 5. The increase in C(18:0) fatty acid that occurred in membranes of warm-adapted fish was greatest for ethanolamine phosphoglycerides, but increases also occurred in other phospholipid fractions and in membrane neutral lipids.     

Blood Lipids in Antarctic and in Temperate-Water Fish Species

Antarctic fish live in very cold water and have adapted to this exceptional environment. Hemoglobin is absent or very low; yet these fish still have erythrocytes, and from these we prepared ghost-like membranes. We studied for the first time the lipid composition of ghost membranes and of plasma in Antarctic fish (C. hamatus and T. bernacchii) and compared our results with those obtained for temperate-water fish (C. auratus and A. anguilla taken from Lake Trasimeno, Perugia, Italy). The membranes of Antarctic fish were richer in glycerophospholipid (especially phosphatidylethanolamine), whereas the membranes of temperate-water fish were richer in sphingomyelin. Unsaturated fatty acids were particularly abundant in Antarctic fish: C. hamatus had long-chain unsaturated fatty acid (especially C22:6 ω-3), whereas T. bernacchii had shorter unsaturated fatty acyl chains (c16:1, ω-7). On the other hand, C. auratus and A. anguilla were particularly rich in C16:0, which constituted more than one-half of the total fatty acid. Plasma lipids (both phospholipid and cholesterol) were much more abundant in temperate-water fish. The differences in phospholipid content were mainly due to choline glycerolipids. Measures of membrane fluidity inferred from the fluorescence anisotropy of DPH indicated that the membranes from Antarctic fish were more fluid at any measured temperature than those obtained from fish living in temperate waters. The ability to live in a very cold environment has therefore been achieved by the two Antarctic species tested in this paper by different strategies, but with the same results on fluidity.     

Lipid Peroxides in the Free Radical Pathophysiology of Brain Diseases

1. Polyunsaturated fatty acids are essential for normal neural cell membrane functioning because many membrane properties, such as fluidity and permeability, are closely related to the presence of unsaturated and polyunsaturated side chains. Lipid peroxidation results in loss of membrane polyunsaturated fatty acids and oxidized phospholipids as polar species contributing to increased membrane rigidity.2. Polyunsaturated fatty acids are released from membrane phospholipids by a number of enzymic mechanisms involving the receptor-mediated stimulation of phospholipase A₂ and phospholipase C/diacylglycerol lipase pathways.3. The overstimulation of excitatory amino acid (EAA) receptors stimulates the activities of lipases and phospholipases, and this stimulation produces changes in membrane phospholipid composition, permeability, and fluidity, thus decreasing the integrity of plasma membranes.4. Alterations in properties of plasma membranes may be responsible for the degeneration of neurons seen in neurodegenerative diseases. Two major processes may be involved in neuronal injury caused by the overstimulation of EAA receptors. One is a large Ca²⁺ influx and the other is an accumulation of free radicals and lipid peroxides as a result of neural membrane phospholipid degradation. It is suggested that calcium and free radicals act in concert to induce neuronal injury in acute trauma (ischemia and spinal cord injury) and in neurodegenerative diseases.     

Root Plasma Membrane Lipid Changes in Relation to Water Transport in Pepper: a Response to NaCl and CaCl<Subscript>2</Subscript> Treatment

Seeds ofCapsicum annuum were grown hydroponically in a nutrient medium with or without NaCI and with supplemented Ca²⁺. Plasma membranes were isolated from roots using a two-phase aqueous polymer technique. The lipid composition (fatty acids, phospholipids and sterols) of the purified plasma membrane was determined. In the presence of NaCI, changes in lipid composition were shown, driving the membrane to a more rigid state. This was accomplished by an increase of (i) the saturation of fatty acids, (ii) the content of stearic acid versus palmitic acid, and (iii) the sterols concentration in the membrane. The changes in the phospholipid composition were also related to NaCI, which reverted when Ca²⁺ was also present in the nutrient solution. Furthermore, the alterations of plasma membrane lipid composition under salinity and calcium can be related to water transport properties of the membrane, but other physiological responses have to be taken into account.     

The molecular organization of nerve membranes

Summary The lipid content and composition from an axolemma-rich preparation isolated from squid retinal axons was analyzed.The lipids, which accounted for 45.5% of the dry weight of this membrane, were composed of 22% cholesterol, 66.7% phospholipids and 5.2% free fatty acids. The negatively charged species phosphatidyl ethanolamine (37%), phosphatidyl serine (10%) and lysophosphatidyl ethanolamine (4%) made up 51% of the phospholipids. The amphoteric phosphatidyl choline and sphingomyelin accounted for 39% and 4%, respectively.The relative distribution of fatty acids in each of the isolated phospholipids was studied. The most remarkable feature of these phospholipids was the large proportion of long-chain polyunsaturated fatty acids. The 226 acyl chain accounted for 37% in phosphatidyl ethanolamine, 21.7% in phosphatidyl choline, 17.5% on phosphatidyl serine and 20.3% in sphingomyelin (all expressed as area %).The molar fraction of unsaturated fatty acids reached 65% in phosphatidyl ethanolamine and 42.0 and 44.8% in phosphatidyl choline and phosphatidyl serine, respectively. The double bond index in these species varied between 1.0 and 2.6.The lipid composition of the axolemma-rich preparation isolated from squid retinal axons appears to be similar to other excitable plasma membranes in two important features: (a) a low cholesterol/phospholipid molar ratio of 0.61; and (b) the polyunsaturated nature of the fatty acid of their phospholipids.This particular chemical composition may contribute a great deal to the molecular unstability of excitable membranes.The preceding papers of this series were published inArchives of Biochemistry and Biophysics.     

Characterization of Phospholipids in Insulin Secretory Granules and Mitochondria in Pancreatic Beta Cells and Their Changes with Glucose Stimulation

The lipid composition of insulin secretory granules (ISG) has never previously been thoroughly characterized. We characterized the phospholipid composition of ISG and mitochondria in pancreatic beta cells without and with glucose stimulation. The phospholipid/protein ratios of most phospholipids containing unsaturated fatty acids were higher in ISG than in whole cells and in mitochondria. The concentrations of negatively charged phospholipids, phosphatidylserine, and phosphatidylinositol in ISG were 5-fold higher than in the whole cell. In ISG phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine, and sphingomyelin, fatty acids 12:0 and 14:0 were high, as were phosphatidylserine and phosphatidylinositol containing 18-carbon unsaturated FA. With glucose stimulation, the concentration of many ISG phosphatidylserines and phosphatidylinositols increased; unsaturated fatty acids in phosphatidylserine increased; and most phosphatidylethanolamines, phosphatidylcholines, sphingomyelins, and lysophosphatidylcholines were unchanged. Unsaturation and shorter fatty acid length in phospholipids facilitate curvature and fluidity of membranes, which favors fusion of membranes. Recent evidence suggests that negatively charged phospholipids, such as phosphatidylserine, act as coupling factors enhancing the interaction of positively charged regions in SNARE proteins in synaptic or secretory vesicle membrane lipid bilayers with positively charged regions in SNARE proteins in the plasma membrane lipid bilayer to facilitate docking of vesicles to the plasma membrane during exocytosis. The results indicate that ISG phospholipids are in a dynamic state and are consistent with the idea that changes in ISG phospholipids facilitate fusion of ISG with the plasma membrane-enhancing glucose-stimulated insulin exocytosis.     

Lipid composition of the isolated rat intestinal microvillus membrane

1. Rat intestinal microvillus plasma membranes were prepared from previously isolated brush borders and the lipid composition was analysed. 2. The molar ratio of cholesterol to phospholipid was greatest in the membranes and closely resembled that reported for myelin. 3. Unesterified cholesterol was the major neutral lipid. However, 30% of the neutral lipid fraction was accounted for by glycerides and fatty acid. 4. Five phospholipid components were identified and measured, including phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine, sphingomyelin and lysophosphatidylcholine. Though phosphatidylethanolamine was the chief phospholipid, no plasmalogen was detected. 5. In contrast with other plasma membranes in the rat, the polar lipids of the microvillus membrane were rich in glycolipid. The cholesterol:polar lipid (phospholipid+glycolipid) ratio was about 1:3 for the microvillus membrane. Published data suggest that this ratio resembles that of the liver plasma membrane more closely than myelin or the erythrocyte membrane. 6. The fatty acid composition of membrane lipids was altered markedly by a single feeding of safflower oil. Membrane polar lipids did not contain significantly more saturated fatty acids than cellular polar lipids. Differences in the proportion of some fatty acids in membrane and cellular glycerides were noted. These differences may reflect the presence of specific membrane glycerides.     

Microsomal Membrane Changes during the Ripening of Apple Fruit

The changes in leakage and viscosity of microsomal membranes from apples (Malus sylvestris cv Calville de San Sauveur) at different stages of ripening were examined. These changes were correlated with those in the lipid composition of the membranes, sterols, phospholipids, and fatty acids of the phospholipids. The greatest changes in membrane properties occurred as the fruit reached its climacteric and this corresponded with a change in the sterol:phospholipid ratio in the membranes. Changes were also found in fatty acid unsaturation level, but primarily in the postclimacteric stage of ripening.     

Sterol carrier protein-2 expression alters plasma membrane lipid distribution and cholesterol dynamics

Although sterol carrier protein-2 (SCP-2) binds, transfers, and/or enhances the metabolism of many membrane lipid species (fatty acids, cholesterol, phospholipids), it is not known if SCP-2 expression actually alters the membrane distribution of lipids in living cells or tissues. As shown herein for the first time, expression of SCP-2 in transfected L-cell fibroblasts reduced the plasma membrane levels of lipid species known to traffic through the HDL-receptor-mediated efflux pathway: cholesterol, cholesteryl esters, and phospholipids. While the ratio of cholesterol/phospholipid in plasma membranes of intact cells was not changed by SCP-2 expression, phosphatidylinositol, a molecule important to intracellular signaling and vesicular trafficking, and anionic phospholipids were selectively retained. Only modest alterations in plasma membrane phospholipid percent fatty acid composition but no overall change in the proportion of saturated, unsaturated, monounsaturated, or polyunsaturated fatty acids were observed. The reduced plasma membrane content of cholesterol was not due to SCP-2 inhibition of sterol transfer from the lysosomes to the plasma membranes. SCP-2 dramatically enhanced sterol transfer from isolated lysosomal membranes to plasma membranes by eliciting detectable sterol transfer within 30 s, decreasing the t(1/2) for sterol transfer 364-fold from >4 days to 7-15 min, and inducing formation of rapidly transferable sterol domains. In summary, data obtained with intact transfected cells and in vitro sterol transfer assays showed that SCP-2 expression (i) selectively modulated plasma membrane lipid composition and (ii) decreased the plasma membrane content cholesterol, an effect potentially due to more rapid SCP-2-mediated cholesterol transfer from versus to the plasma membrane.     

A new role for apolipoprotein E: modulating transport of polyunsaturated phospholipid molecular species in synaptic plasma membranes

Phospholipids and their acyl group composition are important in providing the proper membrane environment for membrane protein structure and function. In particular, the highly unsaturated phospholipids in synaptic plasma membranes in the CNS are known to play an important role in modulating receptor function and neurotransmitter release processes. Apolipoprotein E (apoE) is a major apolipoprotein in the CNS, mediating the transport of cholesterol, phospholipids and their fatty acids, particularly in reparative mechanisms during neuronal injury. This study was performed to determine whether deficiency in the apoE gene contributes to an alteration of the phospholipids in synaptic plasma membranes. Phospholipid molecular species were identified and quantitated by HPLC/electrospray ionization-mass spectrometry. Analysis of the different phospholipid classes in membranes of apoE-deficient and C57BL/6 J mice indicated no obvious differences in the distribution of different phospholipid classes but substantial differences in composition of phospholipid molecular species. Of special interest was the prevalence of phospholipids (phosphatidylcholine, diacyl-phosphatidylethanolamine, and phosphatidylserine) with 22:6n-3 in both the sn-1 and sn-2 positions of SPM and these phospholipid species were significantly higher in apoE-deficient mice as compared to control mice. Since polyunsaturated fatty acids in neurons are mainly supplied by astrocytes, these results revealed a new role for apoE in regulating polyunsaturated phospholipid molecular species in neuronal membranes.     

Influence of dietary source of docosahexaenoic and arachidonic acids on their incorporation into membrane phospholipids of red blood cells in term infants

Here we studied whether the chemical structure of dietary arachidonic and docosahexaenoic acids in full-term infant diets affects their incorporation into erythrocyte membrane phospholipids. From birth to 3 months, infants were fed breast milk (n = 9) or formula milk containing arachidonic acid and docosahexaenoic acid provided by egg phospholipids (n = 10) or by low-eicosapentaenoic acid fish oil and fungal triglycerides (n = 10). We compared the fatty acid composition of erythrocyte phosphatidylethanolamine, phosphatidylcholine and sphingomyelin before and after administration of the experimental diet. At 3 months, infants on formula milk showed lower concentrations of docosahexaenoic acid (in phosphatidylcholine and in phosphatidylethanolamine) and arachidonic acid (in phosphatidylcholine) than those receiving breast milk. We conclude the incorporation of the two fatty acids into erythrocyte phospholipids depends mainly on the lipid composition of the diet received rather than the chemical form in which they are delivered.     

Phospholipid composition and phospholipid asymmetry of ram spermatozoa plasma membranes

The phospholipid composition of ram spermatozoa plasma membranes has been investigated. An exclusively high participation of the choline- and ethanolamine-plasmalogens in the phosphatidylcholine and phosphatidylethanolamine fractions has been established. Phosphatidylcholine of ram spermatozoa plasma membranes contains a great amount of polyunsaturated fatty acids. The phospholipid distribution in spermatozoa plasma membrane was investigated. It was established that the choline containing phospholipids are situated mainly in the outer membrane lipid monolayer, whereas diphosphatidylglycerol and phosphatidylserine are localized predominantly in the inner monolayer. The rest of the phospholipids are evenly distributed among the two monolayers. Ram spermal plasma membranes exhibit high phospholipase A2 activity.     

Phospholipid and fatty acid composition of tetrodotoxin receptor-rich membrane fragments from Electrophorus electricus

To study the interaction of voltage-sensitive Na⁺-channels with membrane lipids, the phospholipid and fatty acid composition of highly purified membrane fragments from the remarkably differentiated plasma membrane of Electrophorus electricus has been analyzed. After density gradient fractionation and carrier free electrophoresis, fractions with up to 30 pmol tetrodotoxin binding/mg protein can be obtained, which may correspond to a 50% pure preparation of the extrasynaptic part of the excitable face. Phospholipid classes and cholesterol are separated by one-dimensional thin-layer chromatography in acidic and alkaline solvent systems. The following mean molar contents are found: 40% phosphatidylcholine, 23% phosphatidylserine, 30% phosphatidylethanolamine and 7% sphingomyelin. In a series of 11 animals, significant deviations from these mean values have been observed. The fatty acid composition of the phospholipids has been determined by gas chromatography. Phosphatidylcholine contains more than 50% 16:0, and about 20% unsaturated fatty acids in the C-18 group. Compared to other plasma membrane fractions, this phospholipid is the least differentiated. By contrast, phosphatidylethanolamine and phosphatidylserine show many characteristics in different membrane fractions, especially in their unsaturated components representing more than 50%. 22:6, as the major constituent in these fractions, accounts for a quarter to a third of all fatty acids in these fractions. 18:0 is the main saturated component in these two phospholipids with abundances of typically a quarter or less of all fatty acids. Knowledge of the lipid composition of these excitable membranes may help to conserve binding and structural properties when analyzing lipid-sensitive Na⁺-channels in vitro. It is also useful as a guideline for systematic reconstitution studies.     

The effect of phosphate deficiency on membrane phospholipid composition of bean (Phaseolus vulgaris L.) roots

Plasma membranes were isolated from roots of bean (Phaseolus vulgaris L.) plants cultured on phosphate sufficient or phosphate deficient medium. The phospholipid composition of plasma membranes was analyzed and compared with that of the microsomal fraction. Phosphate deficiency had no influence on lipid/protein ratio in microsomal as well as plasma membrane fraction. In phosphate deficient roots phospholipid content was lower in the plasma membrane, but did not change in the microsomal fraction. Phosphatidylcholine and phosphatidylethanolamine were two major phospholipids in plasmalemma and microsomal membranes (80 % of the total). After two weeks of phosphate starvation a considerable decrease (about 50 %) in phosphatidylcholine and phosphatidylethanolamine in microsomal membranes was observed. The decline in two major phospholipids was accompanied by an increase in phosphatidic acid and lysophosphatidylcholine content. The effect of alterations in plasma membrane phospholipids on membrane function e.g. nitrate uptake is discussed.     

The fatty acid composition of phospholipids and absorption spectra of lipid extracts from lamprey,frog, and rat erythrocytes

The work studies the content and fatty acid composition of phospholipids as well as the absorption spectra of lipid extracts from red blood cells of poikilothermal and homoiothermal animals at different evolutionary levels. The objects of study include two poikilothermal species, the river lamprey (Lampetra fluviatilis) that uses oxygen dissolved in water, and the common frog (Rana temporaria) that consumes oxygen both from water and from air. A homoithermal animal is the white rat (Rattus rattus) that inhabits the terrestrial-aerial environment. The animals are studied in winter and spring. The phospholipid content in lamprey blood plasma is found to be twice higher than that in its erythrocytes. In the frog and the rat, the ratio is reverse. Determination of the fatty acid lipid composition of red blood cell phospholipids suggests that membranes in the lamprey are denser than in the frog. As for the fatty acids in the erythrocyte fraction of rat blood, they appear to be less diverse, with a double prevalence of saturated acids over unsaturated ones and devoid of long chain (C22) ω3 fatty acids. All of this results in a lower degree of unsaturation and a denser packing of fatty acids in the membrane structures of rat erythrocytes. The mechanism of reversible binding of O₂ molecules to hemoglobin in erythrocytes is discussed. Presumably, the mechanism of interaction between molecules of O₂ and molecules of water prevents the exchange interaction of electrons of the hemoglobin iron atoms with an oxygen molecule. This is confirmed by our obtained absorption spectra, which show that in the lipid extract almost totally devoid of water the heme isolated from erythrocytes is converted to hemin.     

Changes in the fatty acid profiles of red blood cell membrane phospholipids in human neonates during the first month of life

We have studied the changes in the fatty acid profiles of red blood cell membrane phospholipids in 47 infants who were exclusively fed human milk from birth to 1 month of life. Twenty blood samples were obtained from cord, 15 at 7 days and 12 at 30 days after birth. Membrane phospholipids were obtained from erythrocyte ghosts by thin-layer chromatography and fatty acid composition was determined by gas liquid chromatography. Phosphatidylcholine showed the most important changes during early life; stearic, w6 eicosatrienoic and arachidonic acids decreased whereas oleic and linoleic acids increased. In phosphatidylethanolamine, palmitic and stearic acid declined and oleic, linoleic and docosahexenoic acids increased with advancing age. Small changes were noted for individual fatty acids in phosphatidylserine. In sphingomyelin stearic acid increased from birth to 1 month and linoleic, arachidonic and nervonic acids decreased. Total polyunsaturated fatty acids of the w6 series greater than 18 carbon atoms increased with advancing age in phosphatidylethanolamine and decreased in choline and serine phosphoglycerides and in sphingomyelin. Long chain fatty acids derived from linoleic acid decreased in phosphatidylcholine but increased in ethanolamine and serine phosphoglycerides. The different behavior in the changes observed in fatty acid patterns for each erythrocyte membrane phospholipid may be a consequence of its different location in the cell membrane bilayer and specific exchange with plasma lipid fractions.     

Alterations in lipid composition and fluidity of liver plasma membranes in copper-deficient rats

In view of the importance of membrane fluidity on cell functions, the influence of phospholipid acyl groups on membrane fluidity, and the changes in lipid metabolism induced by copper (Cu) deficiency, this study was designed to examine the influence of dietary Cu on the lipid composition and fluidity of liver plasma membranes. Male Sprague-Dawley rats were divided into two dietary treatments, namely Cu deficient and Cu adequate. After 8 weeks of treatment, liver plasma membranes were isolated by sucrose density gradient centrifugation. The lipid fluidity of plasma membranes, as assessed by the intramolecular eximer fluorescence of 1,3-di(1-pyrenyl) propane, was significantly depressed by Cu deficiency. In addition, Cu deficiency significantly reduced the content of arachidonic and palmitoleic acids but increased the docosatetraenoic and docosahexaenoic acids of membrane phospholipids. This alteration in unsaturated phospholipid fatty acid composition, especially the large reduction in arachidonic acid, may have contributed to the depressed membrane fluidity. Furthermore, Cu deficiency also markedly altered the fatty acid composition of the triacylglycerols associated with the plasma membranes. Thus, the lipid composition and fluidity of liver plasma membranes are responsive to the animal's Cu status.