The influence of dietary lipids on the composition and membrane fluidity of rat hepatocyte plasma membrane

Weanling male Wistar rats were fed for five weeks on standard rat chow (23 g fat/kg diet) or one of four synthetic diets with butterfat, coconut oil, corn oil, or fish oil as the main lipid source (100 g fat/kg diet). In all diets, 10% of the fat was provided as corn oil to prevent essential fatty acid deficiency. Significant differences were observed in the saturated, monounsaturated, and polyunsaturated fatty acid composition, and in the ratio of cholesterol to phospholipid, in the hepatocyte membranes. The fluidity of hepatocyte plasma membranes was assessed using the fluorescence recovery after photobleaching technique and steady-state fluorescence anisotropy of diphenylhexatriene. No significant differences were found in the fluidity of plasma membranes between animals on the different fat diets, despite diet-induced changes in their fatty acid composition. However, the proportion of lipid free to diffuse in the plasma membrane varied with diet, being significantly greater (P<0.05) in animals fed chow (63.7%), coconut oil (61.5%), and butterfat (57.6%) diets than in those fed the corn oil (47.3%) diet. Animals fed fish oil showed an intermediate (50.0%) proportion of lipid free to diffuse. The data support the hypothesis that dietary lipids can change both the chemical composition and lateral organization (lipid domain structure) of rat hepatocyte plasma membranes.     

Red blood cell tocopherol and liver tocopherol in hyperlipemic rats as compared with plasma tocopherol

In rats with hyperlipemia induced by Triton WR-1339, changes in tocopherol concentrations in plasma and RBC were compared with those in the liver and its subcellular fractions, microsomes and mitochondria. After daily injection with Triton, plssma total lipids at 3 days and 7 days, respectively, showed elevation 6.5 times and 15 times as high as those in the control rats, and triglycerides showed the most predominant elevation. With the hyperlipemia, the concentrations of tocopherol in RBC and the subcellular fractions decreased, as plasma lipids and plasma tocopherol increased, while no change occurred in tocopherol concentrations in liver homogenates. The changes in the ratio of tocopherol to total lipids in plasma coincided with changes in tocopherol concentrations in the RBC and subcellular fractions.     

Role of membrane lipids in the immunological killing of tumor cells: I. Target cell lipids

The metabolic and physical properties of tumor cells that are associated with their ability to resist or escape from immune attack have been investigated. The susceptibility of P815 murine-mastocytoma cells to immune killing can be modulated. Culturing the cells with adriamicin or with hydrocortisone increases or decreases, respectively, the sensitivity of the cells to killing by antibody (Ab) plus complement (C); in addition, culturing the cells with mitomycin C or hydrocortisone increases or decreases, respectively, the sensitivity of the cells to killing by cytotoxic T lymphocytes (CTL). The susceptibility of the cells to Ab-C killing correlates with the ability of the cells to synthesize complex cellular lipids, but not DNA, RNA, protein, or carbohydrate. Further, tumor cells rendered sensitive to Ab-C killing by adriamycin are decreased in total lipid content and in their cholesterol/phospholipid mole ratio; hydrocortisone-treated resistant cells showed the opposite effects. The ability of tumor cells to resist CTL killing did not correlate with their total cellular lipid synthesis, but did correlate with the synthesis and composition of specific cellular phospholipids. In addition, tumor cells increased in sensitivity to Ab-C killing exhibited an increase in cell surface membrane fluidity, whereas cells increased in suceptibility to CTL attack showed an increase in their net negative cell surface charge density. These data show certain unique chemical and physical properties of tumor cells to be of fundamental importance for their ability to resist either humoral or cell-mediated immunologic attack; modulation of one or another of these cellular properties results in a change in the cells' susceptibility to immune killing by antibody plus C or by cytotoxic T lymphocytes. Presented at the 73rd Annual Meeting of the American Oil Chemists' Society in Toronto, Canada, May 1982.     

Boreal freshwater fish diet modifies the plasma lipids and prostanoids and membrane fatty acids in man

The effect of fish diet on 43 healthy male students was studied. They ate a fish-containing meal for 15 weeks on an average of 3.7 times per week. Twenty-one of them voluntarily restricted their lipid intake while the rest ate normally. Controls continued their usual eating habits (19 students). The meals consisted of Finnish freshwater fish (87%) (vendace, pike, perch and rainbow trout) and brackish water fish (13%) (Baltic herring) that provided about 1 g of ω-3 polyunsaturated fatty acids per day (0.25 g eicosapentaenoic acid and 0.55 g docosahexaenoic acid). During the diet, ω-3 fatty acids increased in erythrocyte ghosts and platelets at the expense of ω-6 fatty acids. The concentration of serum cholesterol diminished in those fish consumers who lowered their lipid intake. Apolipo-protein A₁ and B were lowered in both fish-consuming groups. Triglyceride levels also showed a tendency to decrease. The formation of thromboxane B₂ during incubation of whole blood decreased in both fish-consuming groups. The decrease of plasma 6-keto-PGF_1α was not statistically significant, if compared with the controls. The results obtained indicate that a moderate intake of fish-containing meals has some beneficial effects on the plasma lipid and prostanoid metabolism, when coronary heart disease risk factors are considered.     

Role of membrane lipids in the immunological killing of tumor cells: II. Effector cell lipids

Peritoneal macrophages (MØ) from mice become cytotoxic after incubation in lymphokine (LK)-rich supernatants of antigen-stimulated spleen cell cultures. Tumoricidal activity is evident with MØ treated with LK for 4 hr, becomes maximal after 8–12 hr incubation and decreases to control levels by 24–36 hr. To gain insight into LK-induced functional changes, the lipid composition of MØ cultured with LK for 0–36 hr was analyzed by high pressure liquid chromatography. LK induced marked changes in MØ lipid composition: cellular content of cholesterol (CHOL) and polyunsaturated fatty acids increased 2- to 3-fold after 8 hr when the cells showed maximal tumoricidal activity. Cellular lipid and fatty acid content returned to control levels by 24 hr when the MØ had lost tumoricidal activity. These changes were not observed with equal numbers of MØ cultured in control supernatants. To analyze further the role of CHOL and unsaturated fatty acids in MØ tumor cytotoxicity, MØ were enriched in CHOL or linolenic acid (18∶3) and tested for their ability to kill 1023 tumor cells. Within 1 hr of culture, MØ showed a 3- to 4-fold increase in CHOL or 18∶3 content. 18∶3-enriched cells were markedly tumoricidal, whereas controls cultured in delipidized medium alone or enriched with saturated fatty acid were not cytotoxic. CHOL-enriched MØ were not tumoricidal; indeed, these cells were inhibited in their killing after treatment with LK compared to MØ cultured in delipidized medium with LK alone. These results suggest that UFA aids, whereas CHOL negates, expression of MØ tumor cytotoxicity.     

Fish oil fatty acid esters of phytosterols alter plasma lipids but not red blood cell fragility in hamsters

In an attempt to combine the hypocholesterolemic properties of plant sterols with the hypotriglyceridemic action of fish oil FA, plant sterols have recently been esterified to fish oil n−3 PUFA. The objective of this study was to determine the effects of plant sterols esterified to n−3 PUFA on plasma lipid levels and erythrocyte fragility. For 5 wk, male Golden Syrian hamsters were fed diets varying in cholesterol and plant sterol content: (i) Noncholesterol (semipurified diet with no added cholesterol or plant sterols) (ii), Cholesterol (0.25% cholesterol) (iii), Sterols (0.25% cholesterol plus 1% nonesterified plant sterols), or (iv) Fish oil esters of plant sterols (0.25% cholesterol plus 1.76% EPA and DHA sterol esters, providing 1% plant sterols). The addition of fish oil esters of plant sterols to the cholesterol diet decreased (P=0.001) plasma total cholesterol levels by 20%, but nonesterified plant sterols did not have such a beneficial impact. In addition, non-HDL cholesterol concentrations were 29% lower in hamsters fed fish oil esters of plant sterols than in hamsters fed nonesterified plant sterols (P<0.0001). Despite higher (P<0.0001) plant sterol levels in whole erythrocytes of hamsters fed nonesterified plant sterols and fish oil esters of plant sterols compared with hamsters fed no plant sterols, no difference was observed in erythrocyte fragility. The present results show that EPA and DHA esters of plant sterols have a hypocholesterolemic effect in hamsters, and that these new esters of plant sterols exert no detrimental effect on erythrocyte fragility.     

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.     

myo-Inositol trispyrophosphate: a novel allosteric effector of hemoglobin with high permeation selectivity across the red blood cell plasma membrane

myo‐Inositol trispyrophosphate (ITPP), a novel membrane‐permeant allosteric effector of hemoglobin (Hb), enhances the regulated oxygen release capacity of red blood cells, thus counteracting the effects of hypoxia in diseases such as cancer and cardiovascular ailments. ITPP‐induced shifting of the oxygen–hemoglobin equilibrium curve in red blood cells (RBCs) was inhibited by DIDS and NAP‐taurine, indicating that band 3 protein, an anion transporter mainly localized on the RBC membrane, allows ITPP entry into RBCs. The maximum intracellular concentration of ITPP, determined by ion chromatography, was 5.5×10^?3 M , whereas a drop in concentration to the limit of detection was observed in NAP‐taurine‐treated RBCs. The dissociation constant of ITPP binding to RBC ghosts was found to be 1.72×10^?5 M . All data obtained indicate that ITPP uptake is mediated by band 3 protein and is thus highly tissue‐selective towards RBCs, a feature of major importance for its potential therapeutic use.     

Skeletal muscle membrane lipids and insulin resistance

Skeletal muscle plays a major role in insulin-stimulated glucose disposal. This paper reviews the range of evidence in humans and experimental animals demonstrating close associations between insulin action and two major aspects of muscle morphology: fatty acid composition of the major structural lipid (phospholipid) in muscle cell membranes and relative proportions of major muscle fiber types. Workin vitro andin vivo in both rats and humans has shown that incorporation of more unsaturated fatty acids into muscle membrane phospholipid is associated with improved insulin action. As the corollary, a higher proportion of saturated fats is linked to impairment of insulin action (insulin resistance). Studiesin vitro suggest a causal relationship. Among polyunsaturated fatty acids (PUFA) there is some, but not conclusive, evidence that ω-3 (n−3) PUFA may play a particular role in improving insulin action; certainly a high n−6/n−3 ratio appears deleterious. In relation to fiber type, the more highly oxidative, insulin-sensitive type 1 and type 2a fibers have a higher percentage of unsaturated fatty acids, particularly n−3, in their membrane phospholipid, compared to the insulin-resistant, glycolytic, type 2b fibers. These variables, however, can be separated and may act in synergy to modulate insulin action. It remains to establish whether lifestyle (e.g., dietary fatty acid profile and physical activity), genetic predisposition, or a combination are the prime determinants of muscle morphology (particularly membrane lipid profile) and hence insulin action.     

Cholesterol metabolism during cell growth: Which role for the plasma membrane?

Parenchyma proliferation is accompanied by a peculiar modification of the cholesterol metabolism involving both the growing tissue and the plasma compartment. The increase of cholesterol synthesis and uptake has been largely described in the literature and mainly ascribed to the increased requirement of cholesterol for new membrane biogenesis. The dramatic reduction of cholesterol efflux, which probably contributes to the increase of cholesterol esterification and accumulation, has also been largely described, although, further to acting as a prompt pool for membrane biogenesis requirements, its significance and possible influence on cholesterol homeostasis during growth has been almost completely neglected. In this short review, the most widely known modifications and new insights into the cholesterol metabolism during the growth of normal and tumoral cells will be discussed. Particular attention will be paid to the most widely known modifications of cholesterol storage and efflux. The possible implication of proteins in membrane cholesterol translocation causing cholesterol to be directed towards the ER for esterification by ACAT rather than being released by the appropriate external acceptor, i.e. HDL, during proliferation will be discussed.     

Intake of different eicosapentaenoic acid-containing lipids and fatty acid pattern of plasma lipids in the rats

The ethyl ester of eicosapentaenoic acid (EPA) is the only pure EPA-containing lipid available in bulk for oral administration. However, there is doubt as to whether EPA ethyl ester can efficiently increase the plasma levels of EPA in comparison with the ability of other kinds of EPA-containing lipids to do so. Therefore, two other kinds of EPA-containing lipids were prepared to study the efficiency of oral administration of those lipids for increasing the EPA content in plasma phospholipids and cholesteryl esters. EPA-containing lipids which were investigated were [A], 1,2,3-trieicosapentaenoyl-glycerol, [B] 2-eicosapentaenoyl-phosphatidylcholine and [C] ethyl ester of EPA. An adjusted amount of lipids [A], [B] and [C] was administered to rats through a gastric tube for 4 days (the first experiment) or for 10 days (the second experiment), and the fatty acid composition of plasma phospholipids and cholesteryl esters was determined. In the first experiment, there were no significant differences in the efficiency for increasing EPA levels in either phospholipids or cholesteryl esters among the lipids. In the second experiment, the EPA levels of both plasma phospholipids and cholesteryl esters of rats administered ethyl ester of EPA were significantly higher than those of rats administered 2-eicosapentaenoyl-phosphatidylcholine. The EPA levels of the rats administered 1,2,3-trieicosapentaenoylglycerol were between the levels of the two groups mentioned above, but the differences in the EPA levels were not significant. Although an ethyl ester-type molecule is not a naturally occurring lipid, ethyl ester of EPA is equal to 1,2,3-trieicosapentaenoyl-glycerol and appears to be superior to 2-eicosapentaenoyl-phosphatidylcholine as to the efficiency for increasing EPA levels in total plasma phospholipids and plasma cholesteryl esters.     

Genetic variability of human plasma and erythrocyte lipids

Genetic variation of fasting plasma lipids, lipoproteins and erythrocyte membrane lipids was studied in 67 sets of like-sexed twins and 3 sets of triplets. All of the plasma lipids were more variable in dizygotic twins than monozygotic twins with the exception of phosphatidyl ethanolamine, but only cholesteryl esters, lecithin, phosphatidyl inositol and β-lipoprotein showed significant genetic variation. In contrast, no significant genetic variability was found in any of the erythrocyte membrane lipids and erythrocyte phosphatidyl ethanolamine had significantly greater variation in monozygotic twins. Two sets of twins had an extra lipoprotein band (slow α1); in one family the variant appeared to be segregating as a dominant trait. Presented in part at the ISF-AOCS World Congress, Chicago, September 1970.     

The effects of dietary phospholipids enriched with phosphatidylethanolamine on bile and red cell membrane lipids in humans

The role of phospholipids in biliary cholesterol solubilization and crystallization has only recently begun to be appreciated. Phospholipid vesicles are believed to be the metastable carrier from which cholesterol nucleates. Cholesterol crystallization is influenced by the phospholipid species in bile. Feeding rats and hamsters with diets enriched in phospholipids or their precursors, especially ethanolamine, resulted in reduced cholesterol saturation of bile. Although whole phospholipids are normal dietary constituents, the effects and safety of phospholipid components have not been tested in humans. In the present study, we have evaluated the effects of a dietary phospholipid mixture, enriched with phosphatidylethanolamine, on human bile and red blood cell membrane lipid composition. Five ambulatory volunteers having a chronic indwelling T-tube, with an intact enterohepatic circulation, were investigated. Thirty-six grams of phospholipids (54% phosphatidylethanolamine, 54% linoleyl acyl chains) were added to their daily diet for fourteen days. Biliary nucleation time, cholesterol carriers, as well as plasma, red blood cell membrane, and bile lipid compositions, were monitored. Following phospholipid supplementation, the proportion of linoleyl chains (18:2) in biliary phospholipids increased significantly from 31.1±1.2 to 37.7±5.3%, while that of oleyl chains (18:1) decreased from 11.4±1.6 to 9.6±1.1%. These changes were accompanied by an increase of linoleate and its metabolite, arachidonate, in red cell membranes. Phospholipid feeding did not cause any side effects, and no significant changes in biliary nucleation time, cholesterol, phospholipid, or bile salt concentrations, or in the distribution of cholesterol within micelles or vesicles. We conclude that phospholipid feeding is safe, and can be effective as a vehicle for lecithin fatty acyl chain modulation of bile and lipid membranes. These findings may provide a basis for a controlled modulation of biliary phospholipids to increase cholesterol solubility in bile.     

Abnormal plasma lipids of patients withRetinitis pigmentosa

Retinitis pigmentosa (RP) is a hereditary retinal degeneration of unknown etiology, resulting in progressive night blindness, loss of peripheral vision, abnormal retinal pigmentation and reduced electroretinographic response. Docosahexaenoic acid (22∶6ω3) is found in high concentration in the rod outer segment membranes of the retina. Previous reports of low 22∶6ω3 in blood lipids or phospholipids in RP patients prompted us to evaluate the complete fatty acid (FA) profiles of plasma phospholipids (PL), cholesteryl esters, triglycerides (TG) and nonesterified fatty acids (NEFA) in ten patients with RP. In the PL fraction, we found significantly depressed levels of 22∶6ω3, 22∶5ω3, total ω3, 22∶5ω6, 22∶4ω6 and total ω6 polyunsaturated FA (PUFA), and elevated total saturated acids. Plasma TG showed normal levels of PUFA, normal total saturated FA and total monounsaturated FA. The NEFA fraction showed significant elevation in total saturated FA with depressed total ω6 PUFA. Evidence is accumulating that RP is associated with abnormal PUFA and lipid metabolism. Based in part on a paper presented at the Third International Congress on Essential Fatty Acids and Eicosanoids, Adelaide, Australia, March 1992.     

Effect of eicosatetraynoic acid on liver and plasma lipids

Groups of rats were fed a fat-free diet supplemented with 0.5% safflower oil (control) or the control diet containing 0.5% of 5,8,11,14-eicosatetraynoic acid (TYA). Blood was collected weekly and plasma lipids analyzed. After 4 weeks, the animals were killed and the liver lipids were analyzed in detail. The acetylenic fatty acid perturbed plasma neutral lipid and phospholipid class concentrations and reduced growth rates. Liver triglyceride concentrations were reduced dramatically in the TYA fed animals, suggesting interference with complex lipid synthesis. Plasma and liver triglycerides were shifted to higher molecular weight species suggesting that TYA affected fatty acid metabolism. The phospholipids showed an accumulation of 18∶2 and a fall in 20∶4 percentages indicating an inhibition in the conversion of linoleate to arachidonate. All major lipid classes exhibited an increase in 18∶1 levels. Analysis of the octadecenoate positional isomers indicated the proportion of oleate increased substantually in all lipid classes whereas vaccenate proportions had fallen dramatically. All of the data collectively suggest that TYA inhibits the elongation of unsaturated fatty acids. A group of rats bearing hepatoma 7288CTC were also fed the TYA diet. Host liver lipids were affected by TYA similar to normal TYA fed animals, but the effects on hepatoma lipids were marginal.     

An automated shotgun lipidomics platform for high throughput,comprehensive, and quantitative analysis of blood plasma intact lipids

Blood plasma has gained protagonism in lipidomics studies due to its availability, uncomplicated collection and preparation, and informative readout of physiological status. At the same time, it is also technically challenging to analyze due to its complex lipid composition affected by many factors, which can hamper the throughput and/or lipidomics coverage. To tackle these issues, we developed a comprehensive, high throughput, and quantitative mass spectrometry‐based shotgun lipidomics platform for blood plasma lipid analyses. The main hallmarks of this technology are (i) it is comprehensive, covering 22 quantifiable different lipid classes encompassing more than 200 lipid species; (ii) it is amenable to high‐throughput, with less than 5 min acquisition time allowing the complete analysis of 200 plasma samples per day; (iii) it achieves absolute quantification, by inclusion of internal standards for every lipid class measured; (iv) it is highly reproducible, achieving an average coefficient of variation of <10% (intra‐day), approx. 10% (inter‐day), and approx. 15% (inter‐site) for most lipid species; (v) it is easily transferable allowing the direct comparison of data acquired in different sites. Moreover, we thoroughly assessed the influence of blood stabilization with different anticoagulants and freeze‐thaw cycles to exclude artifacts generated by sample preparation. Practical applications: This shotgun lipidomics platform can be implemented in different laboratories without compromising reproducibility, allowing multi‐site studies and inter‐laboratory comparisons. This possibility combined with the high‐throughput, broad lipidomic coverage and absolute quantification are important aspects for clinical applications and biomarker research. This MS‐based automated shotgun lipidomics platform for comprehensive analysis of the blood plasma lipidome (covering 22 lipid classes) achieves high inter‐day and inter‐site reproducibility and accuracy and enables unprecedented large scale lipidomics studies.     

Effect oftrans fatty acids on plasma lipids,platelet function and systolic blood pressure in stroke-prone spontaneously hypertensive rats

To investigate the effect oftrans fatty acids on plasma lipid levels and systolic blood pressure, hydrogenated corn oil was fed to SHRSP (stroke-prone spontaneously hypertensive rats) and WKY (Wistar-Kyoto) rats for 30 days. Significantly lower systolic blood pressure and plasma total cholesterol were observed in SHRSP rats fedtrans fatty acids when compared with rats fedcis fatty acids from olive oil. In addition, higher HDL cholesterol and lower VLDL plus chylomicron cholesterol levels were found in SHRSP rats fedtrans fatty acids. Although no significant changes of systolic blood pressure and plasma total cholesterol levels were observed in WKY rats aftertrans fatty acids treatment, WKY rats fedtrans fatty acids had lower plasma LDL cholesterol and higher HDL cholesterol levels. In addition, platelet aggregation induced by collagen was decreased in WKY rats fedtrans fatty acids. It is interesting thattrans fatty acids increased the activity of plasma lecithin:cholesterol acyltransferase (LCAT) in both SHRSP and WKY rats. The observed influence oftrans fatty acids on plasma lipid levels, systolic blood pressure and platelet aggregation suggests thattrans fatty acids might prevent thrombotic disorders in SHRSP rats.     

Plasma membrane lipids of bovine adrenal chromaffin cells

The lipid composition of plasma membranes isolated from bovine adrenal chromaffin cells has been determined. Choline and ethanolamine phosphatides were predominant; the level of lyso compounds was very low. The amount of cholesterol and the cholesterol/phospholipid molar ratio was low compared to those of the other subcellular fractions of chromaffin cells. A complex pattern of neutral glycolipids was observed in contrast to that of gangliosides.     

On the orientation of lipids in chloroplast and cell membranes

The widespread recognition of the corpuscular nature of membrane ultrastructure demands re-evaluation of established concepts of their molecular organization. Many aspects of membrane physiology, composition, and metabolism provide support for the proposal that most membranes consist of two-dimensional polymers of lipoprotein subunits. Such a model allows the activity, specificity, and adaptability attributed to biological membranes. Evidence which supports this corpuscular model for membranes and some inadequacies of the bimolecular lipid leaflet model are pointed out. The lamellae of plant chloroplasts are membranes which clearly consist of subunits (quantasomes). Their four surfactant lipids and pigments comprise 50% of the lipoprotein subunits. In each of these surfactant lipids there is found a limited and specific group of fatty ester components. This phenomenon suggests that the hydrocarbon chain of the fatty esters may specifically complement certain hydrophobic amino acid sequences in the membrane protein. The protein, then, would determine the sites where the lipid will be most firmly bound. It is proposed that the lipids of membrane subunits are bound by hydrophobic association of the hydrocarbon chains regions within the interior of the protein. The resulting two-dimensional lipoprotein aggregate would possess the strongly anionic charged groups of the phospholipids on its surface. Metabolically-driven alterations in conformation of such a flexible lipoprotein ion exchange membrane allows a consistent interpretation of biological membrane transport phenomena.     

Human platelet lipids and their relationship to blood coagulation

There is now reasonable agreement on the sequence of physiological and biochemical events leading to fibrin formation, and phospholipids are an important part of this process. The phosphatides are ordinarily provided by platelets, and it appears that a lipoprotein complex is responsible for this activity. The anatomic site of this complex is not known, but evidence is presented that it may be a property of the platelet membrane. Methods for the study of platelet lipids including fatty acids and aldehydes are described, and include silicic acid column and paper chromatography, as well as thin-layer and gas-liquid chromatographic procedures. These are also being utilized in studies of subcellular platelet particles, where only limited amts of biological material are available for study. It is stressed that experimental results obtained from studies on isolated lipids should be interpreted with a certain degree of caution. It is unlikely that they are available as such in in vivo coagulation, and the drastic procedures used for their extraction and isolation may alter their basic physiological properties.