Synthesis and polymorphic phase behaviour of polyunsaturated phosphatidylcholines and phosphatidylethanolamines

A series of phosphatidylcholines and phosphatidylethanolamines was synthesized containing two acyl chains of the following polyunsaturated fatty acids: linoleic acid (18:2), linolenic acid (18:3), arachidonic acid (20:4) and docosahexaenoic acid (22:6). In addition two phospholipids with mixed acid composition were synthesized: 16:0/18:1_c phosphatidylcholine and 16:0/18:1_c phosphatidylethanolamine. The structural properties of these lipids in aqueous dispersions in the absence and in the presence of equimolar cholesterol were studied using ³¹P-NMR, freeze fracturing and differential scanning calorimetry (DSC).The phosphatidylcholines adopt a bilayer configuration above 0°C. Incorporation of 50 mol% of cholesterol in polyunsaturated species induces a transition at elevated temperatures into structures with ³¹P-NMR characteristics typical of non-bilayer organizations. When the acyl chains contain three or more double bonds, this non-bilayer organization is most likely the hexagonal H_II phase, 16:0/15:1_c phosphatidylethanolamine shows a bilayer to hexagonal transition temperature of 75°C. The polyunsaturated phosphatidylethanolamines exhibit a bilayer to hexagonal transition temperature below 0°C which decreases with increasing unsaturation and which is lowered by approximately 10°C upon incorporation of 50 mol% of cholesterol. Finally, it was found that small amounts of polyunsaturated fatty acyl chains in a phosphatidylethanolamine disproportionally lower its bilayer to hexagonal transition temperature.     

Ischemia-Induced Changes in Cerebral Mitochondrial Free Fatty Acids, Phospholipids, and Respiration in the Rat

Abstract: Changes in the free fatty acid pool size and fatty acyl chain composition of mitochondrial membrane phospholipids and their relation to disruption of mitochondrial function were examined in rat brains after 30 min of cerebral ischemia (Pulsinelli-Brierley model) and 60 min of normoxic reoxygenation. During ischemia, significant hydrolysis of polyunsaturated molecular species from diacyl phosphatidylcholine, particularly fatty acyl 20:4 (arachidonic acid; 20% decrease) and 22:6 (docosahexaenoic acid; 15% decrease), was observed. Thirty minutes of ischemia caused a 16% loss of 18:2 (linoleic acid) from phosphatidylethanolamine. Recirculation for 60 min did not return the polyunsaturated fatty acid content of phospholipids to normal. Total content of free fatty acids increased during ischemia, particularly 18:2 and 22:6, which exhibited the most dramatic rise. The free fatty acid pool size continued to increase during 60 min of recirculation. The respiratory control ratio decreased significantly during 30 min of ischemia with no apparent recovery following 60 min of reoxygenation. The degree of free radical-mediated lipid peroxidation in mitochondria was significantly increased during ischemia and reperfusion. It was concluded that (a) 30 min of cerebral ischemia caused differential degradation in each of the phospholipid classes and preferential hydrolysis of the polyunsaturated molecular species and (b) 60 min of normoxic reperfusion failed to promote reacylation of the mitochondrial phospholipids and restoration of normal respiration.     

The acyl composition of mammalian phospholipids: an allometric analysis

Data concerning the acyl composition of tissue phospholipids from mammal species, ranging in size from the shrew (7 g) to cattle (370 kg), has been collated from the literature and analysed allometrically. Phospholipids from heart, skeletal muscle, liver and kidney exhibited similar allometric trends whereby phospholipids had a significant decrease in unsaturation index (number of double bonds per 100 acyl chains) as species body size increased whilst there was no change in the percent of unsaturated acyl chains. Whilst total polyunsaturate content did not change with body mass, both heart and skeletal muscle phospholipids showed a significant allometric decrease in the omega-3 polyunsaturate content. The content of the highly polyunsaturated docosahexaenoic acid (22:6 n-3) in phospholipids showed significant and substantial allometric decline with increasing body mass in all four tissues (exponents ranged from -0.19 in liver to -0.40 in skeletal muscle). Brain phospholipids showed no allometric trends in acyl composition and were highly polyunsaturated in all species. These trends are discussed in light of the hypothesis that the relative content of polyunsaturated acyl chains in membranes, and especially docosahexaenoate (22:6 n-3), can act as a membrane pacemaker for metabolic activity.     

Effects of hypothyroidism on the distribution and fatty acyl composition of phospholipids in sarcoplasmic reticulum of fast skeletal muscle of the rat

The distribution of phospholipids and fatty acyl composition of individual phospholipids in sarcoplasmic reticulum from fast skeletal muscle of hypothyroid and euthyroid (control) rats have been determined. Hypothyroidism resulted in a 24% decrease in the phosphatidylethanolamine (PE) content and a concomitant increase in the phosphatidylcholine (PC) content of the sarcoplasmic reticulum. The amounts of other phospholipids and cholesterol remained unaffected. Fatty acyl compositions of PE and PC were quantitatively different, but hypothyroidism affected these compositions similarly. Changes included an increase in the proportions of docosahexaenoic (22:6(n - 3)), arachidonic (20:4(n - 6)), icosatrienoic (20:3(n - 6)) and stearic (18:0) acids and a decrease in those of linoleic (18:2(n - 6)), palmitic (16:0) and oleic (18:1(n - 9)) acids. The effects of hypothyroidism on the phospholipid distribution could be reversed by treatment of hypothyroid animals with thyroid hormone for a period of 14 days (10 micrograms T3/100 g body weight per 2 days). The fatty acyl composition of the phospholipids was also restored to the euthyroid values by this treatment. Exceptions were 18:2 and 22:6 in PE, in which case reversal was significant but not complete, and 18:2, 20:4 and 22:6 in PC. The levels of these acids in PC were not reversed to the euthyroid values after the 14-day treatment, but rather the opposite occurred.     

N-Acylation of ethanolamine phospholipids by acyl transfer does not involve hydrolysis

N-Acylethanolamine phospholipids occur in infarcted but not in normal canine myocardium. Their synthesis is catalyzed by a membrane-bound, Ca2+-requiring N-acyltransferase (transacylase) which transfers acyl groups from the sn-1 position of various phospholipids including phosphatidylethanolamine to the amino group of ethanolamine phospholipids. When dog heart mitochondria are incubated in media containing Ca2+ and H2(18)O, the resulting N-acylethanolamine phospholipids do not accumulate 18O in either the amide or 1-O-acyl groups. The results indicate that acyl transfer occurs without hydrolysis, most likely through an acyl-enzyme complex which may be covalently linked.     

PI3K–Akt signaling controls PFKFB3 expression during human T-lymphocyte activation

It is commonly accepted that brain phospholipids are highly enriched with long-chain polyunsaturated fatty acids (PUFAs). However, the evidence for this remains unclear. We used HPLC–MS to analyze the content and composition of phospholipids in rat brain and compared it to the heart, kidney, and liver. Phospholipids typically contain one PUFA, such as 18:2, 20:4, or 22:6, and one saturated fatty acid, such as 16:0 or 18:0. However, we found that brain phospholipids containing monounsaturated fatty acids in the place of PUFAs are highly elevated compared to phospholipids in the heart, kidney, and liver. The relative content of phospholipid containing PUFAs is ~ 60% in the brain, whereas it is over 90% in other tissues. The most abundant species of phosphatidylcholine (PC) is PC(16:0/18:1) in the brain, whereas PC(18:0/20:4) and PC(16:0/20:4) are predominated in other tissues. Moreover, several major species of plasmanyl and plasmenyl phosphatidylethanolamine are found to contain monounsaturated fatty acid in the brain only. Overall, our data clearly show that brain phospholipids are the least enriched with PUFAs of the four major organs, challenging the common belief that the brain is highly enriched with PUFAs.     

Age-associated changes in central nervous system glycerolipid composition and metabolism

In this review, changes in brain lipid composition and metabolism due to aging are outlined. The most striking changes in cerebral cortex and cerebellum lipid composition involve an increase in acidic phospholipid synthesis. The most important changes with respect to fatty acyl composition involve a decreased content in polyunsaturated fatty acids (20:4n-6, 22:4n-6, 22:6n-3) and an increased content in monounsaturated fatty acids (18:1n-9 and 20:1n-9), mainly in ethanolamine and serineglycerophospholipids. Changes in the activity of the enzymes modifying the phospholipid headgroup occur during aging. Serine incorporation into phosphatidylserine through base-exchange reactions and phosphatidylcholine synthesis through phosphatidylethanolamine methylation increases in the aged brain. Phosphatidate phosphohydrolase and phospholipase D activities are also altered in the aged brain thus producing changes in the lipid second messengers diacylglycerol and phosphatidic acid.     

Identification of biosynthetic precursors for the endocannabinoid anandamide in the rat brain

Anandamide is an endogenous signaling lipid that binds to and activates cannabinoid receptors in the brain and peripheral tissues. The endogenous precursors of anandamide, N-arachidonoyl phosphatidylethanolamines (NArPEs), are a family of complex glycerophospholipids that derive from the exchange reaction of an arachidonoyl group between the sn-1 position of phosphatidylcholine and the primary amine of phosphatidylethanolamine catalyzed by N-acyl transferase activity. A precise characterization of the molecular composition of NArPE species generating anandamide has not yet been reported. In the present study, using liquid chromatography coupled to electrospray ionization ion-trap mass spectrometry, we identified the major endogenous NArPE species, which mainly contained sn-1 alkenyl groups (C16:0, C18:0, C18:1) and monounsaturated (C18:1) or polyunsaturated (C20:4, C22:4, C22:6) acyl groups at the sn-2 position of the glycerol backbone. Using rat brain particulate fractions, we observed a calcium-dependent increase in both NArPEs and anandamide formation after incubation at 37 degrees C for 30 min. Furthermore, a targeted lipidomic analysis showed that Ca(2+) specifically stimulated the formation of PUFA-containing NArPE species. These results reveal a previously unrecognized preference of brain N-acyl transferase activity for polyunsaturated NArPE and provide new insights on the physiological regulation of anandamide biosynthesis.     

The acylation of lysophosphoradylglycerocholines in guinea-pig heart mitochondria.

The importance of the deacylation-reacylation pathway for attaining the desired fatty acid composition in microsomal phospholipids has been well established. It is not clear, however, whether this mechanism is of equal importance in mitochondria. The absence of acyltransferase activity in mammalian heart mitochondria has been reported in a number of studies. In the present study we report the presence of acyltransferase activities for lysophosphoradylglycerocholines in guinea-pig heart mitochondria. This enzyme showed properties that were considerably different from those of the microsomal enzymes. Of all the acyl-CoAs tested (C18:0, C18:1, C18:2 and C20:4) the mitochondrial enzyme utilized only linoleoyl-CoA as fatty acyl donor and utilized both 1-acyl-sn-glycero-3-phosphocholine and 1-alkenyl-sn-glycero-3-phosphocholine as fatty acyl acceptors. The presence of significant quantities of fatty acids other than linoleate at the C-2 position of mitochondrial acylglycerophosphocholines, coupled with the specificity of the enzyme for linoleoyl-CoA, suggest that, in addition to reacylation, other mechanisms play a significant role in producing the molecular composition of these phospholipids found in the mitochondria.     

Fatty acid composition of total lipids and phospholipids of membrane preparations of transport ATPases

The fatty acid composition of total lipids and phospholipids of duck salt gland Na,K-ATPase (outer plasma membrane) and of rabbit skeletal muscle Ca-ATPase (intracellular membrane) was investigated. The bulk of Na,K-ATPase fatty acids is represented by palmitic (16:0), oleic (18:1), stearic (18:0) and arachidonic (20:4) acids. The duck salt gland is characterized by rather a high content of unsaturated fatty acids, especially of arachidonic acid. The unsaturation index of total-lipid fatty acids increases during purification of these preparations in the following order: homogenate greater than microsomal fraction greater than purified enzyme. The fatty acid composition of Na,K-ATPase total lipids and phospholipids reveals certain differences. Phospholipids contain more stearic and liholeic (18:2) acids than total lipids, but the level of arachidonic acid in them is twice as low. Besides, phospholipids were found to contain polyunsaturated docosohexaenic (22:6) acid. The bulk of fatty acids of rabbit skeletal muscle Ca-ATPase total lipids and phospholipids is represented by 16:0, 18:0, 18:1 and 18:2 acids. The content of polyunsaturated fatty acids in this preparation is much lower than in duck salt gland Na,K-ATPase. The fatty acid composition of total lipids and phospholipids in rabbit skeletal muscle Ca-ATPase differ insignificantly. The differences in the fatty acid composition of membrane preparations under study is conditioned mainly by the fractional composition of their lipids.     

Occurrence of N-acylethanolamine phospholipids in fish brain and spinal cord

N-Acylethanolamine phospholipids were identified in the central nervous system of the fresh water fish, pike (Esox lucius) and carp (Cyprinus carpio), at levels ranging from 0.1 to 0.9% of total phospholipid. The N-acylethanolamine phospholipids of carp brain were isolated and characterized by chemical, biochemical and spectroscopic methods. Two major species, 1,2-diacyl-sn-glycero-3-phospho(N-acyl)ethanolamines (approx. 30%) and 1-O-(1'-alkenyl)-2-acyl-sn-glycero-3-phospho(N-acyl)ethanolamines (approx. 70%) were identified. The N-acyl groups of each species consisted primarily of 16:0 (approx. 60%) but also contained 16:1, 18:0 and 18:1 (approx. 10% each) and a number of trace constituents. The N-acylethanolamine phospholipids had O-acyl and O-alkenyl group compositions similar but not identical to those of the ethanolamine phospholipids of the same tissue. N-Acylethanolamine phospholipids were present in all subcellular fractions of carp brain, except mitochondria.     

Regulation of β-adrenoceptor properties and the lipid milieu in heart muscle membranes during stress

The purpose of this study was to examine changes in fatty acyl chain composition of major cardiac phospholipids in relation to down-regulation of -adrenoceptors during various forms of stress or chronic adrenergic stimulation. Analysis of the fatty acid profile of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in sarcolemma or cardiac muscle membranes showed partial replacement of 18:2n-6 by 20:4n-6 in PC and replacement of both 18:2n-6 and 20:4n-6 by 22:6n-3 in PE during daily administration of epinephrine or norepinephrine for 7 or 15 days, respectively These changes in membrane PC and PE coincided with down-regulation or the decrease in Bmax of -adrenoceptors during adrenergic stimulation. Cardiac membrane response to other forms of stress or chronic adrenergic stimulation such as neonatal stress, restriction stress or restricted food intake was expressed in the same way, that is replacement of 18:2n-6 by 20:4n-6 in PC and replacement of 18:2n-6 and 20:4n-6 by 22:6n-3 in PE.Conclusion: Adaptation to stress includes a decrease in the density of binding sites or down-regulation of -adrenoceptors in sarcolemma synchronized with specific alterations in the fatty acyl chain composition within the membrane bilayer. The changes in the lipid milieu of the membrane may facilitate conformational changes in the transmembrane segment of the receptor forming the ligand binding sites of the -adrenoceptor.     

Fatty acid profiles of brain phospholipid subclasses of rats fed n - 3 polyunsaturated fatty acids of marine or vegetable origin. A two generation study.

The effects of dietary n - 3 polyunsaturated fatty acids (PUFA) on fatty acid profiles of rat brain phospholipid subclasses as well as on heart phosphatidylethanolamine through two generations were examined: Three groups of rats were fed 20 weight% fat diets in which approx. 30% of the fatty acids were polyunsaturated, either 17% linoleic acid + 13% C20(-) + C22 polyunsaturates from fish oil or 17% linoleic + 13% alpha-linolenic acid from linseed oil or 30% linoleic acid. The rats of the two generations were killed as adults at 18 weeks of age. The results demonstrated that fish oil was a better source than alpha-linolenic acid for incorporation of n - 3 PUFA into the examined phospholipids. This was seen both in brain and heart tissue and in both generations of rats. In the brain phosphatidylethanolamine (PE) and phosphatidylserine (PS) similar fatty acid profiles were found in 1st and 2nd generation, but fish oil was more efficient than 18:3(n - 3) in increasing the levels of 22:6(n - 3), 20:5(n - 3), 22:5(n - 3) and reducing 20:4(n - 6) and 22:5(n - 6). Fatty acid profiles of phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2) were affected by dietary fats. In PIP and PIP2 of 2nd generation rats 20:4(n - 6) was reduced from 36 to 29% following fish oil intake, whereas alpha-linolenic acid had no effects. The cholesterol/phospholipid ratio was not affected in the brain, neither was the degree of unsaturation of the phospholipids. In heart PE the highest levels of 20:5(n - 3)(2%) and 22:6(n - 3) (36%) were observed following fish oil intake. However, in rats fed alpha-linolenic acid a considerable increase in the level of 22:6(n - 3) was observed from the 1st (21%) to the 2nd generation (26%).     

Comparative utilization of n-3 polyunsaturated fatty acids by cultured human Y-79 retinoblastoma cells

The Y-79 retinoblastoma cell, a cultured human line derived from the retina, was utilized as a model for investigating the metabolism of n-3 polyunsaturated fatty acids in neural tissue. When cultures were incubated with 5 microM linolenic (18:3), eicosapentaenoic (20:5) or docosahexaenoic (22:6) acids, a low concentration probably representative of physiologic levels, the amount incorporated was 20:5 congruent to 18.3 greater than 22:6. Regardless of which fatty acid was provided, 65-75% of the total uptake accumulated in phosphatidylethanolamine and ethanolamine plasmalogen, suggesting that these phospholipids play an important role in n-3 polyunsaturated fatty acid metabolism. A small amount of 22:6 was converted to 20:5, which was recovered in phosphatidylinositol and phosphatidylserine. Therefore, one metabolic function of 22:6 may be to serve as an intracellular storage pool for the formation of 20:5 through retroconversion. When any of the n-3 polyunsaturates was available, the main fatty acid that accumulated in the cell phospholipids was 22:6. The extent to which 22:6 accumulated, however, depended on the particular n-3 polyunsaturated fatty acid that was available. This suggests that the 22:6 content of a neural cell, and any cellular function dependent on 22:6 content, may be regulated by changes in the type of n-3 polyunsaturate available to the nervous system.     

Changing Fatty Acid Content of Growth Cone Lipids Prior to Synaptogenesis

The developing mouse was used to assess biochemical changes in membrane lipids during the period when nerve growth cones become synapses. Growth cone particles and synaptosomes were simultaneously obtained from common brain homogenates. Incorporation of the essential fatty acid, docosahexaenoic acid (22:6 omega-3), was correlated with the developmental changes in endogenous fatty acid content of growth cones and synaptosomes. Analysis of endogenous lipid content indicated that, at all ages studied, the growth cones contained more arachidonoyl acyl chains (20:4 omega-6) than did synaptosomes. Before the onset of synaptogenesis, levels of arachidonoyl chains increased and levels of 22:6, oleoyl and linoleoyl chains decreased in synaptosomes. Although stearoyl and palmitoyl (16:0) remained stable in synaptosomes, 16:0 decreased in growth cones. With the exception of 16:0 and 20:4, endogenous fatty acyl content of growth cones and synaptosomes became similar by postnatal day 10, which coincides with the onset of synaptogenesis. When 5-day-old mouse pups were injected intraperitoneally with [3H]22:6, the incorporation into growth cone and synaptosome phospholipids was greatest in phosphatidylethanolamine, followed by phosphatidylserine and phosphatidylcholine. Nominal labeling was present in phosphatidic acid and phosphatidylinositol. Labeling in neutral lipids was less than that of phospholipids, with triacylglycerol incorporating most of the neutral lipid label, followed by diacylglycerol and free 22:6. Only the growth cone fraction contained detectable amounts of 22:6-labeled cholesterol esters. The distribution of 22:6 label in plasma 72 h after injection indicated that approximately 60% of the label was in phospholipids with approximately 40% in neutral lipids and less than 5% in free fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hydrolysis of N-acylated glycerophospholipids by phospholipases A2 and D: a method of identification and analysis

We have previously identified N-acylethanolamine phospholipids in infarcted dog heart and in normal fish brain by chemical and enzymatic degradation. We now report that hydrolysis with phospholipase D from Streptomyces chromofuscus removes N-acylethanolamine from N-acylethanolamine phospholipids and lyso N-acylethanolamine phospholipids, or N-acylserine from lyso N-acylserine phospholipids. At acidic pH, a phosphatase present in the phospholipase D preparation further hydrolyzes the resulting phosphatidic acid (PA) or lyso-PA to diacyl- or monoacylglycerol. Because N-acylserine phospholipids are a poor substrate for the phospholipase D, pretreatment with phospholipase A2 (Trimeresurus flavoviridis venom) is used to remove the 2-O-acyl group. Thus, both types of N-acylated phospholipids can be analyzed by consecutive phospholipase A2 and phospholipase D treatment. Reaction products, i.e., free fatty acids, monoacylglycerols and N-acylethanolamine or N-acylserine, are separable by thin-layer chromatography. Both N-acyl components can be further characterized by conversion to the t-butyldimethylsilyl derivatives. The method was used to identify and analyze the N-acylserine phospholipids of bovine brain.     

Liver and heart mitochondria obtained from Adelie penguin (Pygoscelis adeliae) offers high resistance to lipid peroxidation

Lipid peroxidation is generally thought to be a major mechanism of cell injury in aerobic organisms subjected to oxidative stress. All cellular membranes are especially vulnerable to oxidation due to their high concentration of polyunsaturated fatty acids. However, birds have special adaptations for preventing membrane damage caused by reactive oxygen species. This study examines fatty acid profiles and susceptibility to lipid peroxidation in liver and heart mitochondria obtained from Adelie penguin (Pygoscelis adeliae). The saturated fatty acids in these organelles represent approximately 40-50% of total fatty acids whereas the polyunsaturated fatty acid composition was highly distinctive, characterized by almost equal amounts of 18:2 n-6; 20:4 n-6 and 22:6 n-3 in liver mitochondria, and a higher proportion of 18:2 n-6 compared to 20:4 n-6 and 22:6 n-3 in heart mitochondria. The concentration of total unsaturated fatty acids of liver and heart mitochondria was approximately 50% and 60%, respectively, with a prevalence of oleic acid C18:1 n9. The rate C20:4 n6/C18:2 n6 and the unsaturation index was similar in liver and heart mitochondria; 104.33 +/- 6.73 and 100.09 +/- 3.07, respectively. Light emission originating from these organelles showed no statistically significant differences and the polyunsaturated fatty acid profiles did not change during the lipid peroxidation process.     

Neuroprotective effect of N-acylethanolamines in chronic morphine dependence. II. Effect on the rat brain fatty acid composition

The effect of N-acylethanolamines mixture (NAE) with saturated and unsaturated acyl chains on the fatty acid composition of the rat brain under chronic morphine dependence was investigated. Long-term administration of NAE reduced morphine-induced decrease of mono- and polyunsaturated fatty acids in the rat brain crude lipid extract. Furthermore, NAE restored the acyl chain spectrum, especially the content of docosahexaenoic acid in essential phospholipids--phosphatidylcholine and phosphatidylethanolamine. Pharmacological activity of NAE depended on a dose.     

Effects of postdecapitative ischemia and hypoxia on the phosphoglyceride acyl groups of rat brain membranes

Rats subjected to mild hypoxic and postdecapitative ischemic treatments indicated a decrease (8–16%) in the proportion of polyunsaturated acyl groups of diacyl glycerophosphocholines (diacyl-GPC), diacyl glycerophosphoethanolamines (diacyl-GPE), and alkenylacyl glycerophosphoethanolamines (alkenylacyl-GPE) in brain synaptosomes. In general, the acyl group changes due to mild hypoxic treatment were less obvious than those due to the ischemic treatment. The decrease in polyunsaturated acyl groups was marked by an increase in the saturated (16:0 and 18:0) and monoenoic (18:1) acyl groups. Among the polyunsaturated acyl groups, arachidonate (20:4) indicated the greatest decrease in response to ischemic and hypoxic treatments. The decrease in polyunsaturated fatty acids of diacyl glycerophosphocholines was largest in the first minute of ischemic treatment and the first 30 min of hypoxic treatment. After the initial decrease, there was a slight recovery. The biphasic type of change was thought to be due to active reacylation of the lyso phospholipids. This biphasic change, however, was not observed with ethanolamine phosphoglycerides which indicated a steady decrease in the polyunsaturated acyl group content with time of ischemic treatment. The increased hydrolysis of polyunsaturated acyl groups in brain membrane phosphoglycerides due to the ischemic and hypoxic treatments seemed to correlate well with the implication of phospholipase A₂ involvement in eliciting the increase in free fatty acids during brain stimulation.     

Composition of Lipids in Elasmobranch Electric Organ and Acetylcholine Receptor Membranes

The composition of phospholipids from electric organ and from membranes enriched in acetylcholine receptors (AChRs) is analyzed in three elasmobranch fish (Torpedo marmorata, Torpedo californica, and Discopyge tschudii). Irrespective of their purity, AChR-containing membranes are similar to electric organ in lipid and fatty acid composition. The following characteristics are common to the three species: (a) Choline, ethanolamine, and serine glycerophospholipids account for 80-90% of the phospholipids. (b) Their major fatty acid constituents are monoenes, saturates, and long-chain (n-3) polyenes (especially docosahexaenoate). (c) A large proportion of the ethanolamine glycerophospholipids (30-50%) is made up by plasmenylethanolamine, which contains fewer polyenes than phosphatidylethanolamine per mole of lipid. (d) Polyphosphoinositides represent 20-30% of the inositides of electric organ. (e) Phosphatidylinositol and phosphatidate have large proportions of 20- and 22-carbon polyenes. (f) Diphosphatidylglycerol and triacylglycerols are rich in oleate but also contain long-chain polyenes. (g) Sphingomyelin has monoenes and saturates ranging from 14 to 26 carbons. Species-related variations are observed (a) in the ratios between some phospholipid classes and subclasses and (b) in the relative abundance of the major polyunsaturated acyl chains of phospholipids. Despite these differences, the average unsaturation and length of fatty acids in major phospholipid classes are similar for the three species.