Molecular species of sphingomyelin in sphingomyelinase-sensitive and sphingomyelinase-resistant pools of HL-60 cells

This study of sphingomyelin molecular species in undifferentiated and differentiated (granulocytic form) HL-60 cells demonstrated only minor differences in the distribution of species between the sphingomyelinase-sensitive and sphingomyelinase-resistant pools of sphingomyelin in these cells. The two most prominent species of sphingosine present in both the undifferentiated and differentiated cells were those containing 16∶0 (slightly higher in the sphingomyelinase-resistant membranes) and 24∶1N-acyl moieties. Cell differentiation exerted little effect on the distribution of molecular species of sphingomyelin between the sphingomyelinase-sensitive and sphingomyelinase-resistant pools in HL-60 cells, although the levels ofN-palmitoyl sphinganine were significantly lower and theN-nervonoyl sphingosine higher in both pools from the differentiated cells. Our results indicate the same species of sphingomyelin, available at both the outer layer of the plasma membrane and inner layer of the plasma membrane (plus intracellular membranes) of HL-60 cells, serve as precursors for generation of the ceramides that participate in signal transduction processes initiated by cell activation.     

Differences in the phospholipid,cholesterol, and fatty acyl composition of 3T3 and SV3T3 plasma membranes

An analysis of the phospholipid, cholesterol, and phospholipid fatty acyl composition of isolated plasma membranes of 3T3 and SV3T3 mouse embryo cells has been performed. The results show that the plasma membrane of SV3T3 cells contain relatively less phosphatidylethanolamine and sphingomyelin and more cholesterol than 3T3 plasma membranes. The fatty acyl composition of individual phospholipid classes as determined by gas liquid chromatography also showed differences between 3T3 and SV3T3 plasma membranes. The plasma membranes of SV40 transformed 3T3 cells contain: (a) a higher percentage of 18∶1 and less 20∶3 and 20∶4 in phosphatidylethanolamine; (b) a higher percentage of 18∶1 in phosphatidylserine; and (c) a higher percentage of 18∶2 and 20∶4 in phosphatidylinositol.     

Lipids and delta6-desaturase activity alterations in rat liver microsomal membranes induced by fumonisin B1

Alterations in the membrane structure and function of hepatocyte membranes by fumonisin B₁ (FB₁) have been proposed to play an important role in the disruption of growth regulatory effects and hence in the cancer-promoting ability of the mycotoxin. Detailed analyses of lipids in liver microsomal fractions of rats exposed to different dietary levels of FB₁ over a period of 21 d indicated an increase in PC, PE, PI, and cholesterol (Chol). These changes decreased the PC/PE and increased the total phospholipid/Chol ratios. When considering FA content, the quantities of total FA increased (P<0.05) in the major phospholipid fractions as a result of the increased phospholipid levels. However, when considering the relative levels (mg/100 mg of the total FA) of specific FA, the monounsaturated FA (16∶1n−7 and 18∶1n−9) and 18∶2n−6 increased (P<0.05), whereas the long-chain PUFA decreased (P<0.05) in the main phospholipid fractions. Enzyme analyses indicated that the activity of the Δ6-desaturase was significantly reduced in liver microsomal preparations in a dose-dependent manner. An increase in the 20∶3n−6/20∶4n−6 ratio also suggested a decrease in the activity of the Δ5-desaturase. Disruption of microsomal lipid metabolism at different levels by FB₁ could play an important role in the alteration of growth regulatory effects in the liver.     

Effect of essential fatty acid deficiency on lipid composition of basolateral plasma membrane of pig intestinal mucosal cells

The effect of essential fatty acid (EFA) deficiency on the lipid composition of basolateral plasma membranes (BPM) from intestinal mucosal cells was investigated in weaning pigs fed control or EFA-deficient diets for 12 weeks. The phospholipid and cholesterol contents relative to protein were similar in both groups, showing a cholesterol/phospholipid molar ratio of 0.6. The distribution of phospholipid classes was also unaffected by the diet. In contrast, fatty acid profiles of the two phospholipid main classes, phosphatidylcholine and phosphatidylethanolamine were altered by EFA deficiency. Linoleic acid (18∶2n−6) was largely reduced, whereas arachidonic acid (20∶4n−6) only slightly decreased in EFA-deficient pigs. The unsaturation index was essentially maintained by high levels of oleic acid (18∶1n−9) and by conversion of oleic acid to 5,8,11-eicosatrienoic acid (20∶3n−9). Finally, during the period of EFA deficiency, the lipid composition of BPM of the intestinal mucosal cells was little affected, suggesting a preferential uptake of 20∶4n−6 and (or) precursor mobilized from other tissues. However, an effect of dietary treatment on the function of membrane-associated proteins cannot be ruled out.     

Effects of eicosapentaenoic acid and docosahexaenoic acid on plasma membrane fluidity of aortic endothelial cells

We investigated the relative effects of n−3 eicosapentaenoic acid (EPA, 20∶5n−3) and docosahexaenoic acid (DHA, 22∶6n−3) on the plasma membrane fluidity of endothelial cells (EC) cultured from the thoracic aorta by determining fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and its cationic derivative trimethylamino-DPH (TMA-DPH). Fluidity assessed by TMA-DPH demonstrated no significant differences in plasma membranes of vehicle (dimethyl sulfoxide; DMSO)-, EPA-, and DHA-treated EC. Plasma membrane fluidity assessed by DPH polarization, however, was significantly higher in the order of DHA>EPA>DMSO. Total cholesterol content decreased significantly by 28.4 and 15.9% in the plasma membranes of DHA- and EPA-treated cells, respectively. Total phospholipid content remained unaltered in the plasma membranes of the three groups of cells; however, the molar ratio of total cholesterol to phospholipid decreased significantly only in the membranes of DHA-treated EC. The unsaturation index in the plasma membranes of EPA- and DHA-treated cells increased by 35.7 and 64.3%, respectively, compared with that in the plasma membranes of control cells. The activities of catalase and glutathione peroxidase in the whole-cell homogenates, and levels of lipid peroxides in either the whole-cell homogenates or in plasma membrane fractions were not altered in EPA- or DHA-treated EC. These results indicate that the influence of DHA is greater than that of EPA in increasing plasma membrane fluidity of vascular EC. We speculate that the greater effect of DHA compared to EPA is due to its greater ability to decrease membrane cholesterol content or the cholesterol/phospholipid molar ratio, or both, and also to its greater ability in elevating the unsaturation index in the plasma membranes of EC.     

Specificity of polyunsaturated fatty acid release from rat brain synaptosomes

Release of specific polyunsaturated fatty acids from cell membranes may have a significant implication in biological function, considering the involvement of various fatty acids in cell signal transduction. In the present study, release of polyunsaturated fatty acids from rat brain synaptosomes by endogeneous synaptosomal lipase activity was examined in comparison to that by cobra venom phospholipase A₂ (Naja naja naja). Cobra venom phospholipase A₂ (Naja naja naja) preferentially hydrolyzed docosahexaenoic acid (22∶6n−3) from both synaptosomes and lipid muxtures containing similar classes of lipids commonly found in the brain. Arachidonic acid (20∶4n−6) and oleic acid (18∶1n−9) were also hydrolyzed; however, monoene species was hydrolyzed slower than were polyenoic species in synaptosomes. Phosphatidylethanolamine was the most preferred phospholipid class for release of 22∶6n−3 fatty acid from both lipid mixtures and synaptosomes. In contrast to hydrolysis by cobra venom phospholipase A₂, endogenous synaptosomal lipase activity preferentially hydrolyzed 20∶4−6 from rat brain synaptosomes, despite the high abundance of 22∶6n−3 in synaptosomal membranes. Preferential release of 20∶4n−6 was observed over a wide range of pH values and calcium concentrations. Synaptosomal 22∶6 species appeared to be resistant to hydrolysis even after stimulation with various agents such as phorbolmyristate, suggesting that physiological importance of 22∶6−3 in neuronal membranes may not be as the release fatty acid.     

Lipid composition of yoshida ascites hepatoma and of livers and blood plasma from host and normal rats

The lipid composition of Yoshida ascites hepatoma cells was analyzed together with that of ascitic plasma and of livers and blood plasma from host and normal rats. In comparison to normal livers, host livers showed no significant differences in the content of the various lipid classes, but contained a higher percentage of palmitic acid and a lower proportion of arachidonic acid in the major phospholipid classes. In addition, tumor growth induced a marked hypertriglyceridemia in host animals; changes in the concentration of other plasma lipid classes were not statistically significant. The ascitic plasma contained small amounts of lipids mainly constituted by cholesteryl esters and phospholipids. Yoshida hepatoma cells contained less phospholipids in comparison to both host and normal liver, while the increased level of triglycerides and the decrease of free fatty acids were not statistically significant. Hepatoma cells showed appreciable amounts of ether-linked lipids associated in part to neutral lipids (as glyceryl ether diesters) and, in part, to ethanolamine and choline phosphoglycerides. The alkyl groups in GEDE as well as in ethanolamine and choline phosphoglycerides were mainly constituted by C_16∶0 and C_18∶0 followed by C_18∶1. The alk-1-enyl groups in ethanolamine and choline phosphoglycerides were C_16∶0 and C_18∶0 with only a minor proportion of C_18∶1. In comparison to both host and normal liver, Yoshida hepatoma cells showed significant changes in the fatty acid composition of neutral lipids and phospholipids. Some of the major changes consisted of an increase of monoenoic acids associated with a decrease of arachidonic and docosahexaenoic acids in phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol.     

Effects of clofibrate on lipids and fatty acids of mouse liver

Clofibrate administration significantly altered the amount and fatty acid composition of lipids in mouse liver. The net content of phospholipids (PL) increased and that of triacylglycerols (TG) decreased concomitantly with liver enlargement in mice treated for two weeks with this drug (0.5% w/w in the food). The highest increase among PL was in phosphatidylcholine; other components either showed lower increases or, as in the case of sphingomyelin and the plasmalogens, decreased. In all lipid classes the treatment resulted in altered ratios between major saturates, between saturates and monoenes, and between major polyenes. Among these, 20∶3n–6 and 22∶5n–3 increased several-fold, and the 20∶3n–6/20∶4n–6 and 22∶5n–3/22∶6n–3 ratios increased due to a more active formation of the precursors than of the corresponding products. This change affected all glycerolipid classes. Liver sphingomyelin showed a relative enrichment in monoenoic fatty acids like 22∶1 and 24∶1, caused by a net decrease in the amount of saturates, particularly 22∶0 and 24∶0. The stimulated membrane proliferation imposed by clofibrate must increase phospholipid synthesis and, hence, the need for fatty acids. The results suggest that these demands are met mostly by TG acyl groups, either directly or after oxidation/desaturation processes. This was apparently the case for the polyenoic fatty acids of the n-6 and n-3 series. The longer chain (C₂₂ and C₂₄) components decreased, suggesting that their oxidation was stimulated to provide part of the required (C₂₀ and C₂₂) polyenes.     

Occurrence of wax esters and 1-O-alkyl-2,3-diacylglycerols in goat epididymal sperm plasma membrane

Two unusual lipid classes were detected by thin-layer chromatography in the neutral lipids derived from goat cauda-epididymal sperm plasma membrane. The lipids were identified as wax esters and 1-O-alkyl-2,3-diacylglycerols based on chromatographic properties, identity of their hydrolysis products, and infrared/¹H nuclear magnetic resonance spectral evidence. The membrane containedca. 3 and 5 μg/mg protein of wax esters and alkyldiacylglycerols, respectively. The relative proportions of wax esters and alkyldiacylglycerols in the total neutral lipids were 1.5% and 2.4%, respectively. The lipids contained fatty acids with chain lengths of C₁₄ to C₂₂. The major fatty acids of the wax esters were 14∶0, 16∶0, 16∶1ω7, 18∶0 and 18∶1ω9. The fatty acids in alkyldiacylglycerol were 16∶0, 18∶0, 22∶5ω3 and 22∶6ω3. Alkyldiacylglycerol was particularly rich in docosahexaenoic acid 22∶6ω3) representing 30% of the total fatty acids. The alcohols of wax ester were all saturated with C₂₀–C₂₉ carbon chains. The deacylated products derived from alkyldiacylglycerols were identified as hexadecyl, octadecyl and octadec-9′-enyl glycerol ethers.     

Blood lipid docosahexaenoic and arachidonic acid in term gestation infants fed formulas with high docosahexaenoic acid,low eicosapentaenoic acid fish oil

The effect of fish oil high in docosahexaenoic acid (22∶6n−3) and low in eicosapentaenoic acid (20∶5n−3) in formula on blood lipids and growth of full-term infants was studied. Infants were fed formula with about 15% oleic acid (18∶1), 32% linoleic acid (18∶2n−6), 4.9% linolenic acid (18∶3n−3) and 0, 0.10 or 0.22% 22∶6n−3, or 35% 18∶1, 20% 18∶2n−6, 2.1% 18∶3n−3 and 0, 0.11 or 0.24% 22∶6n−3 from 3 d to 16 wk of age (n=16, 18, 17, 21, 17, 16, respectively). The formulae had <0.1% 20∶5n−3 and no arachidonic acid (20∶4n−6). Breast-fed infants (n=26) were also studied. Plasma phospholipid and red blood cell (RBC) phosphatidylcholine (PC) and phosphatidylethanolamine (PE) fatty acids were determined at 3 d and 4, 8, and 16 wk of age. These longitudinal analyses showed differences in blood lipid 22∶6n−3 between breast-fed and formula-fed infants depending on the feeding duration. At 16 wk, infants fed formula with 0.10, 0.11% 22∶6n−3, or 0.22% 22∶6n−3 had similar 22∶6n−3 levels in the plasma phospholipid and RBC PC and PE compared with breast-fed infants and higher 22∶6n−3 than infants fed formula without 22∶6n−3. Formula with 0.24% 22∶6n−3, however, resulted in higher plasma phospholipid 22∶6n−3 than in breast-fed infants at 16, but not 4 or 8 wk of age. Plasma and RBC phospholipid 20∶4n−6 was lower in formula-fed than breast-fed infants, but no differences in growth were found. Higher blood lipid C₂₀ and C₂₂ n−6 and n−3 fatty acids in infants fed formula with 20% 18∶2n−6 and 2.4% 18∶3n−3 compared with 32% 18∶2n−6 and 4.9% 18∶3n−3 show the increase in blood lipid 22∶6n−3 in response to dietary 22∶6n−3 depending on other fatty acids in the formula.     

Fatty acid composition of subcellular particles from sheep platelets and topological distribution of phosphatidylethanolamine fatty acids in the plasma membrane

The fatty acid composition of individual phospholipids in subcellular fractions of sheep platelets and the asymmetrical distribution of phosphatidylethanolamine (PE) fatty acyl chains across the plasma membrane were examined. The main fatty acids of total lipid extracts were oleic (18∶1; 32–41%), linoleic (18∶2, 10–17%), stearic (18∶0; 13–15%), palmitic (16∶0; 11–15%) and arachidonic (20∶4; 8–12%) acids, with a saturated/unsaturated ratio of about 0.4. Each phospholipid class had a distinct fatty acid pattern. Sphingomyelin (SM) showed the highest degree of saturation (50%), with large proportions of behenic (22∶0), 18∶0 and 16∶0 acids. The main fatty acid in PE, phosphatidylserine (PS) and phosphatidylcholine (PC) was 18∶1n−9. Our findings suggest that fatty acids are asymmetrically distributed between thecholineversus the non-choline phospholipids, and also between plasma membranes and intracellular membranes. The transbilayer distribution of PE fatty acids in plasma membranes from non-stimulated sheep platelets was investigated using trinitrobenzenesulfonic acid (TNBS). A significant degree of asymmetry was found, which is a new observation in a non-polar cell. The PE molecules from the inner monolayer contained higher amounts of 18∶2 and significantly less 18∶1 and 20∶5 than those found in the outer monolayer, although no major differences were detected in the transbilayer distribution of total unsaturatedversus saturated PE acyl chains.     

Lipid composition of the pineal organ from rainbow trout (Oncorhynchus mykiss)

The lipid composition of the pineal organ from the rainbow trout (Oncorhynchus mykiss) was determined to establish whether the involvement of this organ in the control of circadian rhythms is reflected by specific adaptations of lipid composition. Lipid comprised 4.9% of the tissue wet weight and triacylglycerols were the major lipid class present (47% of total lipid). Phosphatidylcholine (PC) was the principal polar lipid, and smaller proportions of other phospholipids and cholesterol were also present. Plasmalogens contributed 11% of the ethanolamine glycerophospholipids (EGP). No cerebrosides were detected. The fatty acid composition of triacylglycerols was generally similar to that of total lipids in which saturated, monounsaturated and polyunsaturated fatty acids (PUFA) were present in almost equal proportions. Each of the polar lipid classes had a specific fatty acid composition. With the exception of phosphatidylinositol (PI), in which 20∶4n−6 comprised 27.4% of the total fatty acids, 22∶6n−3 was the principal PUFA in all lipid classes. The proportion of 20∶5n−3 never exceeded 6.0% of the fatty acids in any lipid class. The predominant molecular species of PC were 16∶0/22∶6n−3 and 16∶0/18∶1, which accounted for 33.2 and 28.5%, respectively, of the total molecular species of this phospholipid. Phosphatidylethanolamine (PE) contained the highest level of di-22∶6n−3 (13.0%) of any phospholipid. There was also 4.9% of this molecular species in phosphatidylserine (PS) and 4.1% in PC. In PE, the species 16∶0/22∶6, 18∶1/22∶6 and 18∶0/22∶6 totalled 45.1%, while in PS 18∶0/22∶6 accounted for 43.9% of the total molecular species. The most abundant molecular species of PI was 18∶0/20∶4n−6 (37.8%). The lipid composition of the pineal organ of trout, and particularly the molecular species composition of PI, is more similar to the composition of the retina than that of the brain. Molecular species are abbreviated as follows: e.g., 16∶0/22∶6 PC is 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine.     

Effects of dietary n−3 polyunsaturated fatty acids on phospholipid composition and calcium transport in mouse cardiac sarcoplasmic reticulum

The effects of dietary n−3 and n−6 polyunsaturated fatty acids on the fatty acid composition of phospholipid, Ca⁺⁺· Mg⁺⁺ ATPase and Ca⁺⁺ transport activities of mouse sarcoplasmic reticulum were investigated. Mice were fed a 2 weight percent fat diet containing either 0.5 weight percent ethyl esters of 18∶3n−3, 20∶5n−3 or 22∶6n−3 as a source of n−3 polyusaturated fatty acid or 0.5 weight percent safflower oil as a cource of n−6 polyunsaturated fatty acid for 10 days. Olive oil (2 weight percent) was used as a control diet. Although feeding n−6 polyunsaturated fatty acid induced very little modifications of the phospholipid sarcoplasmic reticulum fatty acid composition, feeding n−3 polyunsaturated fatty acid altered it markedly. Inclusion of 18∶−3, 20∶5n−3 or 22∶6n−3 in the diet caused an accumulation of 22∶6n−3, which replaced 20∶4n−6 and 18∶2n−6 in phospholipid sarcoplasmic reticulum. The saturated fatty acids were significantly increased with a concurrent reduction of 18∶1n−9. These changes in the fatty acid composition resulted in a decrease in the values of the n−6/n−3 polyunsaturated fatty acid ratio and a decrease in the ratio of 20 carbon to 22 carbon fatty acids esterified in the phospholipid sarcoplasmic reticulum. This was associated with a decrease in Ca⁺⁺ uptake by n−3 polyunsaturated fatty acid enriched sarcoplasmic reticulum vesicles as compared with n−6 fatty acid and control diet sarcoplasmic reticulum vesicles. However, neither the affinity for Ca⁺⁺ nor the maximal velocity of ATP hydrolysis activity of Ca⁺⁺·MG⁺⁺ ATPase were altered by the different diets. The data suggest that the incorporation of 22∶6n−3 and/or the decrease of 20∶4n−6 plus 18∶2n−6 in the phospholipid sarcoplasmic reticulum may affect the membrane lipid bilayer structure and make it more permeable to Ca⁺⁺.     

Phospholipids of two strains of dermatophyte,Arthroderma uncinatum

The phospholipid composition of a mutant strain of the dermatophyteArthroderma uncinatum was compared with that of the wild type. Phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, diphosphatidylglycerol, phosphatidylinositol, and phosphatidic acid were present, and there was marked variation in the amounts of phosphatidylcholine, phosphatidylserine, and phosphatidic acid in the two strains. Thus, the ratio of phosphatidylcholine (wild type) to phosphatidylcholine (mutant) was 2∶1; the ratio of phosphatidylserine (wild type) to phosphatidylserine (mutant) was 3∶1 and the ratio of phosphatidic acid (wild type) to phosphatidic acid (mutant) was 1∶5. In both strains, the predominant fatty acid was 18∶2, with 54.0% in the wild type and 46.7% in the mutant. Qualitatively, the same fatty acids, with the exception of C_20∶0, were found in all of the phospholipid classes; C_20∶0, both in the mutant strain (5.79%) and the wild type (trace amounts), was associated with phosphatidylserine. There was a significant difference in the rates of growth of the two strains; the mutant strain grew more rapidly than, and produced three times as much mycelium as, the wild type. The mutant strain also produced larger proportions of total lipid and phospholipid than the wild type; there was 20.5% total lipid and ca. 5% phospholipid in the mutant compared with 15.5% total lipid and 2.6% phospholipid in the wild type.     

Alteration in membrane lipid order and composition in metabolically hyperactive fatty rat adipocytes

We have previously shown that adipose cells from young genetically obese Zucker rats are characterized by very high metabolic activity together with an increase in a wide range of membrane-mediated functions. The aim of the present study was to examine whether the physical properties of the membranes and the composition of the membrane lipids were altered in these cells. Plasma membranes and two intracellular membrane fractions were prepared by differential ultracentrifugation from inguinal adipose cells of 30-day-old obese (fa/fa) and lean (Fa/fa) littermates. The lipid order as measured by steady-state fluorescence polarization of diphenylhexatriene used as probe was markedly decreased in the plasma membranes of obese rat adipose cells. Consistent with this, the cholesterol-to-phospholipid ratio was significantly decreased, and the degree of unsaturation of the phospholipid fatty acids was significantly increased. In intracellular membranes, none of these parameters were altered by the different genotype. In fat cells from obese rats, both plasma and intracellular membranes exhibited a 2-fold decrease in the ratios of n−6/n−3 fatty acids mainly due to an enrichment in docosahexaenoic acid (22∶6n−3). The data show that the fatty genotype is a determinant of membrane lipid order and composition in adipose cells. The alterations reported here for young obese Zucker rat adipocytes might be related to the metabolic hyperactivity of these cells.     

Zinc deficiency in the rat alters the lipid composition of the erythrocyte membrane triton shell

The effect of dietary zinc deficiency on the lipid composition of the erythrocyte membrane Triton shell was determined. Weanling male Wistar rats were fed an egg white-based diet containing <1.0 mg Zn/kg dietad libitum. Control rats were either pair-fed orad libitum-fed the basal diet supplemented with 100 mg Zn/kg diet. A Zn refed group was fed the −Zn diet until day 18 and then pairfed the +Zn diet until day 21. Dietary, Zn deficiency caused an increased cholesterol/phospholipid ratio in Triton shells compared to those from pair-fed controls. Zn deficiency caused a decreased double bond index of fatty acids in phosphatidylinositol (PI) and phosphatidylcholine (PC); there was a decreased proportion of 18∶2n−6 and 22∶4n−6 in PC and 20∶4n−6 in PI as compared to that found in pair-fed controls. All glycerophospholipids that were retained in the shell had a lower double bond index and increased content of 16∶0 and/or 18∶0 relative to the phospholipid in the intact membrane.     

Enhancement of G protein-coupled signaling by DHA phospholipids

The effect of phospholipid acyl chain and cholesterol composition on G protein-coupled signaling was studied in native rod outer segment (ROS) disk and reconstituted membranes by measuring several steps in the visual transduction pathway. The cholesterol content of disk membranes was varied from 4 to 38 mol% cholesterol with methyl-β-cyclodextrin. The visual signal transduction system [rhodopsin, G protein (G_t), and phosphodiesterase (PDE)] was reconstituted with membranes containing various levels of phospholipid acyl chain unsaturation, with and without cholesterol. ROS membranes from rats raised on n−3 fatty acid-deficient and-adequate diets were also studied. The ability of rhodopsin to form the active metarhodopsin II conformation and bind G_t was diminished by a reduction in the level of DHA (22∶6n−3) acyl chains or an increase in membrane cholesterol. DHA acyl chain containing phospholipids minimized the inhibitory effects of cholesterol on the rate of rhodopsin-G_t coupling. The activity of PDE, which is a measure of the integrated signal response, was reduced in membranes lacking or deficient in DHA acyl chains. PDE activity in membranes containing docosapentaenoic acid (DPA, 22∶5n−6) acyl chains, which replace DHA in n−3 fatty acid deficiency, was 50% lower than in DHA-containing membranes. Our results indicate that efficient and rapid propagation of G protein-coupled signaling is optimized by DHA phospholipid acyl chains.     

The effect of dietary zinc deficiency on the lipid composition of the rat erythrocyte membrane

The effect of dietary zinc deficiency in the rat on the lipid composition of the erythrocyte membrane was determined. Weanling male Wistar rats were fed an egg whitebased diet containing <1.0 mg Zn/kg dietad libitum. Control rats were either pair-fed orad libitum-fed the basal diet suppelemented with 100 mg Zn/kg diet. A zinc refed group was fed the −Zn diet until day 18 and then pairfed the +Zn diet until day 21. The voluntary feed restriction associated with dietary zinc deficiency resulted in erythrocyte membranes that had depressed phospholipid/protein and elevated cholesterol/phospholipid ratios. Similarly, all feed restricted groups had elevated 22-carbon n−3 polyunsaturated fatty acid (PUFA) and depressed 22-carbon n−6 PUFA concentrations in alkenylacyl and diacyl glycerophosphoethanolamine, phosphatidylserine and phosphatidylcholine; they also had depressed 24∶2n−6 levels in sphingomyelin. The relative concentrations of phospholipids in the membrane was similar between −Zn and +Zn (ad libitum) groups; however, the −Zn group had significantly less phosphatidylserine relative to +Zn (pair-fed) controls.     

Thermal acclimation and dietary lipids alter the composition,but not fluidity,of trout sperm plasma membrane

The effect of a long-term adaptation of rainbow trout to 8 and 18°C combined with a corn oil-or a fish oil-supplemented diet on the characteristics of the spermatozoan plasma membrane was investigated. The experiment lasted up to 22 mon during which spermatozoa were collected from the mature males. Spermatozoan plasma membranes were isolated by nitrogen cavitation, and the cholesterol content, phospholipid composition and fatty acid pattern were investigated. Membrane viscosity was assessed on whole cells by electron spin resonance using spin-labeled phospholipids. Neither diet nor rearing temperature influenced the cholesterol content of the plasma membrane nor the phospholipid class distribution. The rearing temperature of the broodstock only slightly affected the phospholipid fatty acids. A minor decrease in 18∶0 and increase in monounsaturated fatty acids was observed for the cold-adapted fish. These modifications were not sufficient to affect membrane fluidity, and we conclude that trout spermatozoa do not display any homeoviscous adaptations in these conditions. On the contrary, the dietary fatty acid intake greatly modified the fatty acid profile of plasma membrane phospholipids. The fish oil-fed trout displayed a much higher n−3/n−6 fatty acid ratio than did the corn oil-fed ones, but the 22∶6n−3 levels remained unchanged. Modifications in plasma membrane composition by the diet were obtained although neither of the two diets was deficient in essential fatty acids. The enrichment in n−3 fatty acids, however, did not affect plasma membrane fluidity which was unchanged by the diets.     

Changes in lipid molecular species and sterols of microsomal membranes during aging of potato (Solanum tuberosum L.) seed-tubers

Changes in sterols and the molecular species composition of polar lipids from microsomal membranes were characterized as a prerequisite to determining how lipid chemistry affects membrane susceptibility to peroxidation during aging of potato tubers. Polar lipid content of the microsomal fraction fell 17% (protein basis) as tubers aged from 2 to 38 mon at 4°C. In younger seed-tubers, PC concentration (protein basis) was the highest, followed by digalactosyldiacylglycerol (DGDG), PE, monogalactosyldiacylglycerol (MGDG), and PI. PC and PE increased 14 and 27%, respectively, whereas glycolipids fell 64 and PI 43% with advancing age. These changes resulted in PC and PE dominating the microsomal membrane lipids of 38-mon-old tubers. Nonpositional analysis of lipid molecular species across lipid pools showed an increase in 16∶0/18∶3, 18∶3/18∶3, and 18∶2/18∶3 (PC and PE only), and a decline in 18∶2/18∶2 and 16∶0/18∶2 (except for MGDG) with advancing tuber age. The increase in 18∶3-bearing species effected a linear increase in double-bond index (DBI) of PC and PE during aging. The DBI of DGDG did not change with age; however, it fell 65% for MGDG, resulting in an overall decrease in average microsomal DBI. In addition, Δ5-avenasterol and stigmasterol concentrations increased 1.6- and 3.3-fold, respectively, effecting a significant increase in the sterol/phospholipid ratio with advancing tuber age. The increase in sterol/phospholipid ratio and the possibility that the increased unsaturation of microsomal membranes reflects a compensatory response to maintain optimal membrane function in light of the age-induced loss of galactolipid and PI are discussed.