Changes in composition, biosynthesis, and physical state of membrane lipids occurring upon aging of Mycoplasma hominis cultures.

During the progression of Mycoplasma hominis cultures from the early logarithmic phase to the stationary phase of growth, the total phospholipid content of the cell membranes decreased. Measurement of the amount of the various phospholipids during the growth cycle showed that a decrease in the phosphatidylglycerol (PG) content, accompanied by an increase in the phosphatidic acid content, occurred upon aging of the culture. Pulse labeling experiments revealed that the PG, once formed, is relatively stable, undergoing no detectable turnover in growing cultures of M. hominis. No changes in the fatty acid composition of the membrane phospholipids were observed on aging of the culture, with palmitic acid predominating throughout the growth cycle. The preferential incorporation of palmitate into the phospholipid fraction is apparently caused by the higher activity of the membrane-bound acyl-coenzyme A (CoA):alpha-glycerophosphate transacylase with palmityl-CoA rather than with oleyl-CoA as substrate. The activity of the soluble acyl-CoA synthetase was the same whether palmitate or oleate served as substate. M. hominis membrane preparations contained a PG-synthetase system catalyzing the incorporation of L-alpha-glycerol-3-phosphate into PG. The activity of the PG synthetase system was markedly dependent on the age of the culture, being highest in cells from the early exponential phase of growth while declining sharply thereafter, and thus probably responsible, in part, for the decrease in PG content upon aging of the cells. Electron paramagnetic resonance spectra of a spin-labeled fatty acid incorporated in M. hominis membranes revealed a marked decrease in the freedom of motion of the spin label on aging of the culture. It is proposed that this decrease is due primarily to the decrease in the lipid-to-protein ratio of the membranes and has a marked effect on the activity of membrane-associated enzymes and transport systems.     

Fusion of Spiroplasma floricola cells with small unilamellar vesicles is dependent on the age of the culture.

Small unilamellar vesicles were labeled with the fluorescent probe octadecylrhodamine B chloride and mixed with intact Spiroplasma floricola cells. The increase in fluorescence observed was interpreted as a result of the dilution of the probe in the unlabeled S. floricola membranes because of lipid mixing upon fusion. The progression of S. floricola cultures to the stationary phase of growth was accompanied by a sharp decrease in the ability of the cells to fuse with small unilamellar vesicles. Low fusogenic activity was also detected in cells from cultures that were aged in a growth medium maintained at pH 7.5 throughout the growth cycle. Chemical analysis of the cell membrane preparations isolated from cells harvested at the various phases of growth revealed that the phospholipid content and composition and the cholesterol/phospholipid molar ratio were changed very little upon aging of the cultures. Likewise, no changes in the fatty acid composition of membrane lipids were detected, with palmitic and oleic acids predominating throughout the cycle. Nonetheless, upon aging of S. floricola cultures, a pronounced increase in the levels of both cholesteryl esters, incorporated from the growth medium, and organic peroxides was observed. A decrease in both fluorescence anisotropy of diphenylhexatriene and merocyanine 540 binding to membranes of aged cells was also detected. The possible influence of these changes on the fusogenic activity of the cells is discussed.     

Modification of CaCo-2 cell membrane fatty acid composition by eicosapentaenoic acid and palmitic acid: effect on cholesterol metabolism

Membrane fatty acid composition of CaCo-2 cells was modified by incubating the cells for 8 days in medium containing 100 microM eicosapentaenoic acid or palmitic acid. The effect of membrane fatty acid changes on cholesterol metabolism was then studied. Cells incubated with eicosapentaenoic acid had significant changes in membrane fatty acid composition with an accumulation of 20:5 and 22:5 and a reduction in monoenoic fatty acids compared to cells grown in palmitic acid. Intracellular cholesteryl esters could not be detected in CaCo-2 cells grown in the presence of the n-3 polyunsaturated fatty acid. In contrast, cells incubated with the saturated fatty acid contained 2 micrograms/mg protein of cholesteryl esters. Cells grown in eicosapentaenoic acid, however, accumulated significantly more triglycerides compared to cells modified with palmitic acid. The rate of oleic acid incorporation into triglycerides was significantly increased in cells incubated with eicosapentaenoic acid. CaCo-2 cells modified by eicosapentaenoic acid had lower rates of HMG-CoA reductase and ACAT activities compared to cells modified with palmitic acid. The incorporation of the two fatty acids into cellular lipids also differed. Palmitic acid was predominantly incorporated into cellular triglycerides, whereas eicosapentaenoic acid was preferentially incorporated into phospholipids with 60% of it in the phosphatidylethanolamine fraction. The data indicate that membrane fatty acid composition is significantly altered by growing CaCo-2 cells in eicosapentaenoic acid. These modifications in membrane fatty acid saturation are accompanied by a decrease in the rates of cholesterol synthesis and cholesterol esterification.     

Changes of fatty acids and sterols in apple buds during bud break induced by a plant bioregulator, thidiazuron

The effects of N-phenyl-N'-l,2,3,-thidiazol-5-ylurea (thidiazuron; Dropp; SN 49537) on fatty acids of membrane lipids and sterol content in apple ( Malus domestica Borkh cv. Golden Delicious) buds associated with bud break and bud development were determined. The predominant fatty acids in the membrane lipids of apple buds were palmitic acid (C16:0), linoleic acid (C18:2) and linolenic acid (C18:3). β -Sitosterol and sitosteryl ester were the predominant sterols. An accumulation of unsaturated polar membrane fatty acids started after thidiazuron treatment. A decrease in the percentage of the sitosterol was accompanied by an increase in campesterol and stigmasterol at the beginning of rapid growth. An increase in the ratio of campesterol and stigmasterol to sitosterol and a decrease in the ratio of free sterols to membrane lipids upon breaking of dormancy also occurred in apple buds induced by thidiazuron.     

Increased rates of lipid exchange between Mycoplasma capricolum membranes and vesicles in relation to the propensity of forming nonbilayer lipid structures

We have studied the effects of modification of the endogenous phosphatidylglycerol (PG) and diphosphatidylglycerol (DPG) content of the plasma membrane of Mycoplasma capricolum on the kinetics of spontaneous [14C]cholesterol and 14C-labeled phospholipid exchange between M. capricolum membranes and lipid vesicles. The PG/DPG molar ratio of M. capricolum membranes changed when cells were grown in media supplemented with 0.5 mM CaCl2 and/or egg phosphatidylcholine (PC) (10-20 micrograms/ml), increasing from 3.9 to 6.3 on supplementation with Ca2+; this ratio decreased to 1.1 in media supplemented with PC and to 1.8 in media containing both PC and Ca2+. The ratio of palmitate to oleate in both PG and DPG decreased when cells were grown with PC or with PC and Ca2+. Bilayer disruptions were seen in freeze-fracture electron micrographs of trypsin-treated M. capricolum membranes from cells grown with both Ca2+ and PC, and numerous lipidic particles and other bilayer disruptions were observed in trypsin-treated M. capricolum membranes and their lipid extracts. The rates of spontaneous exchange of 14C-labeled cholesterol and PC from membranes isolated from cells grown with PC and Ca2+ to acceptor lipid vesicles were exchanged by approximately 30%, and the rate of the rapidly exchangeable cholesterol pool in intact cells was enhanced by 64%. The enhancements in cholesterol and PC exchange rates are considered to result from structural defects expected in the M. capricolum membranes obtained from cells grown with Ca2+ supplementation. Our findings parallel previous examples of functional modifications of membranes induced by bilayer instability arising from a pretransitional state leading to the onset of a nonlamellar phase.     

Thermal regulation of the fatty acid composition of lipopolysaccharides and phospholipids of Proteus mirabilis.

The fatty acid composition of the lipid A moiety of the lipopolysaccharide and phospholipid fractions of Proteus mirabilis changed significantly on varying the growth temperature. A decrease in the growth temperature from 43 degrees C to 15 degrees C resulted in a decrease in the palmitic acid content of the lipopolysaccharide from 19.4% of total fatty acids at 43 degrees C to 1.4% at 15 degrees C, and by the appearance of an unsaturated fatty acid residue, hexadecenoic acid. Changes in the 3-hydroxy-myristic acid content of the lipid A were minimal. The decrease in the growth temperature also resulted in a decrease in the saturated fatty acid content of the phospholipid fraction, which was accompanied by an increase in their fluidity, as measured by the freedom of motion of spin-labeled fatty acids incorporated into dispersions made of the phospholipids. Nevertheless, the fluidity obtained with membrane phospholipids extracted from the cells grown at various temperatures were essentially the same when fluidity was determined at the growth temperature, supporting the hypothesis that variations in the fatty acid composition of membrane phospholipids serve to produce membranes having a constant fluidity at different temperatures of growth.     

Thermally induced heterogeneity in microsomal membranes of fatty acid-supplemented Tetrahymena: lipid composition, fluidity and enzyme activity

Thermally induced phase separation was observed to occur in microsomal membranes of the ciliate Tetrahymena pyriformis, using the technique of freeze-fracture electron microscopy. In the present study, we attempted to fractionate the phase-separated membranes which were produced by chilling cells by sucrose density gradient centrifugation. When Tetrahymena was grown in the presence of palmitic acid, cells rapidly incorporated the fatty acid into their phospholipids. The resulting endoplasmic reticulum containing a high level of palmitic acid was more susceptible to thermotropic phase separation. Despite the profound alterations in the fatty acid composition, the cells retained normal growth rate, appearance and cell motility. Smooth microsomes isolated from palmitic acid-supplemented Tetrahymena cells were sonicated and then fractionated into three major subfractions. Fraction-I with lower buoyant density was rich in phospholipids and saturated fatty acids, while Fraction-III with higher density was rather rich in proteins and contained more unsaturated fatty acids in the phospholipids. A significant change was also observed in the polar head composition of phospholipids in these fractions. ESR analysis demonstrated that the extracted lipids from Fraction-III were more fluid than those from Fraction-I. In addition, the motion of the spin probe in the native membranes was more restricted than in extracted lipids. These results indicate that the lipid phase separation causes "squeezing out" of the membrane proteins from the less fluid to the fluid areas. Furthermore, we examined the temperature dependence of the activities of glucose-6-phosphatase and palmitoyl CoA desaturase.     

The effect of variations in growth temperature, fatty acid composition and cholesterol content on the lipid polar head-group composition of Acholeplasma laidlawii B membranes

We have systematically investigated the effect of variations in growth temperature, fatty acid composition and cholesterol content on the membrane lipid polar headgroup composition of Acholeplasma laidlawii B. Two important lipid compositional parameters have been determined from such an analysis. The first parameter studied was the ratio of the two major neutral glycolipids of this organism, monoglucosyldiacylglycerol (MGDG) and diglucosyldiacylglycerol (DGDG). As the former lipid prefers to exist in a reversed hexagonal phase at higher temperatures, with unsaturated fatty acyl chains or in the presence of cholesterol, the ratio of these two lipids reflects the phase state preference of the total A. laidlawii membrane lipids. Although we find that the MGDG/DGDG ratio is reduced in response to an increase in fatty acid unsaturation, increases in growth temperature or cholesterol content reduce this ratio only in cells enriched in a saturated but not an unsaturated fatty acid. The second parameter studied was the ratio of these neutral glycolipids to the only phosphatide in the A. laidlawii membrane, phosphatidylglycerol (PG); this parameter reflects the relative balance of uncharged and charged lipids in the membrane of this organism. We find that the MGDG + DGDG/PG ratio is lowest in cells enriched in the saturated fatty acid even though these cells already have the highest lipid bilayer surface charge density. Moreover, this ratio is not consistently related to growth temperature or changes in cholesterol levels, as expected. We therefore conclude that A. laidlawii strain B, apparently unlike strain A, does not possess coherent regulatory mechanisms for maintaining either the phase preference or the surface charge density of its membrane lipid constant in response to variations in growth temperature, fatty acid composition or cholesterol content.     

Age-related changes in petal membranes from attached and detached rose flowers

Changes in petal membrane properties during aging were studied in cut and in attached rose flowers (Rosa hybrida L., cv Mercedes). Both cut and attached flowers exhibited a growth phase characterized by an increase in fresh weight and an accumulation of membrane components. The growth phase, which was more pronounced in the attached than in the cut flowers, was followed by a senescence phase, characterized by a decrease in fresh weight and a decline in membrane components. In cut flowers, both the growth and the senescence phases were accompanied by a decrease in membrane fluidity and in the ratio of unsaturated to saturated fatty acids, but the ratio of sterol to phospholipid increased. In attached flowers, while both the membrane fluidity and the sterol-to-phospholipid ratio remained unchanged during the growth phase, the senescence phase was accompanied (as in cut flowers) by a decrease in membrane fluidity and an increase in the sterol-to-phospholipid ratio. Unlike in cut flowers, however, the age-related changes in the ratio of unsaturation of fatty acids were not correlated with those of fluidity. Changes in the saturation of phospholipid acyl chains are commonly thought to influence membrane fluidity. Our observations question this view and suggest instead that the ratio of sterol to phospholipid may play the major role in maintaining membrane lipid fluidity.     

Composition and enzyme activities of Spiroplasma citri membranes.

Spiroplasma citri was cultured in three different media that supplied cholesterol and fatty acids from: (i) horse serum, (ii) pleuropneumonia-like organism (PPLO) serum fraction, or (iii) bovine serum albumin-fatty acid-cholesterol. The ability of PPLO serum fraction to support growth varied by lot number. Neither PPLO serum fraction nor the bovine serum albumin medium supported growth as well as the horse serum medium. Analysis of cholesterol, lipid phosphorus, and membrane protein showed the horse serum- and PPLO-grown cells to be indistinguishable, but the bovine serum albumin-grown cells were deficient in lipid phosphorus. The three cultures did not show markedly different fatty acid compositions, but, in all cases, the cultures preferentially incorporated palmitic acid and discriminated against linoleic acid. Cultures grown for different times from logarithmic growth through a degenerative phase showed relatively constant ratios of cholesterol/protein and lipid phosphorus/protein. Fatty acid composition was also relatively constant at the different stages. Adenosine triphosphatase and p-nitrophenyl phosphatase were mainly associated with the membrane, whereas reduced nicotinamide adenine dinucleotide oxidase was either readily removed or not associated with the membrane. The reduced nicotinamide adenine dinucleotide oxidase was inactivated at temperatures above 35 degrees C.     

Rhodopseudomonas acidophila strain 10050 contains photosynthetic LH2 antenna complexes that are not enriched with phosphatidylglycerol,and the phospholipids have a fatty acyl composition that is unusual for purple non-sulfur bacteria

The phospholipid composition of Rhodopseudomonas acidophila strain 10050 grown aerobically or anaerobically in the light was determined. The major phospholipids present in the aerobic cells were phosphatidylethanolamine (PE; 54%), phosphatidylglycerol (PG; 24%) and cardiolipin (diphosphatidylglycerol, DPG) (14%), together with phosphatidylcholine (PC; 5%). On moving the cells to anaerobic photosynthetic growth in the light PE remained the major phospholipid (37-49%), but there was a major change in the proportion of PC, which increased to 31-33%, and corresponding reductions in the contents of PG to 11-16% and DPG to 4-5%. The fatty acid composition of the phospholipids was unusual, compared with other purple non-sulfur photosynthetic bacteria, in that it contained 16:0 (29%), 17:1 (20%) and 19:1 (9%) plus several mainly unsaturated 2-OH fatty acids (9% total) as major components, when grown aerobically in the dark. In contrast when grown photosynthetically under anaerobic conditions there was <2% 17:1 or 19:1 present, while the amounts of 16:1 and 18:1 increased, and 16:0 decreased. The phospholipid composition of the purified light-harvesting complex 2 (LH2) complex was PE (43%), PC (42%) and DPG (15%). Unexpectedly, there was no PG associated with the purified LH2. These findings contrast with previous studies on several other photosynthetic bacteria, which had shown an increase in PG upon photosynthetic growth [Biochem. J. 181 (1979) 339]. The prior hypothesis that phosphatidylglycerol has some specific role to play in the function of light-harvesting complexes cannot be true for Rps. acidophila. It is suggested that specific integral membrane proteins may strongly influence the phospholipid content of the host membranes into which they are inserted.     

Unsaturated fatty acid requirement inEscherichia coli: Mechanism of palmitate-induced inhibition of growth of strain WN1

Summary The minimum requirement for unsaturated fatty acids was investigated inE. coli using a mutant impaired in the synthesis of vaccenic acid. Exogenously supplied palmitic acid was incorporated by this mutant which led to a reduction in the proportion of cellular unsaturated fatty acids. Growth was impaired as the level of saturated fatty acids approached 76% at 37°C and 60% at 30°C. The basis of this growth inhibition was investigated. Most transport systems and enzymes examined remained active in palmitate-grown cells although the specific activities of glutamate uptake and succinic dehydrogenase were depressed 50%. Fluorescent probes of membrane organization indicated that fluidity decreased with palmitate incorportation. Temperature scans with parinaric acid indicated that rigid lipid domains exist in palmitategrown cells at their respective growth temperature. Freeze-fracture electron microscopy confirmed the presence of phase separations (particle-free areas) in palmitate-grown cells held at their growth temperature prior to quenching. The extent of this separation into particle-free and particle-enriched domains was equivalent to that induced by a shift to 0°C in control cells. The incorporation of palmitate increased nucleotide leakage over threefold. The cytoplasmic enzyme -galactosidase was released into the surrounding medium as the concentration of unsaturated fatty acid approached the minimum for a particular growth temperature. Lysis was observed as a decrease in turbidity when cells which had been grown with palmitate were shifted to a lower growth temperature. From these results we propose that leakage and partial lysis are the major factors contributing to the apparent decrease in growth rate caused by the excessive incorporation of palmitate. Further, we propose that membrane integrity may determine the minimum requirement for unsaturated fatty acids inE. coli rather than a specific effect on membrane transport and/or membrane-bound enzymes.     

Characterization of the stimulatory effects of PGF2alpha on the release of arachidonic acid

Fibroblasts derived from a rat carrageenin granuloma were cultured in the presence of radioactive arachidonic acid, palmitic acid and linoleic acid. More than 90% of each labeled fatty acid was incorporated into a phospholipid fraction by the cells in 18 hrs. Arachidonic acid was evenly incorporated into phosphatidylcholine and phosphatidylethanolamine, while both palmitic acid and linoleic acid were almost entirely incorporated into phosphatidylcholine. The position of phosphatidylcholine where the fatty acids were incorporated was different for each fatty acid. The ratio of the amount of fatty acid incorporated into the 2-position to the amount incorporated into the 1-position of phosphatidylcholine for each fatty acid was greater than 90% for arachidonic acid, 2:1 for palmitic acid and 5:1 for linoleic acid. In the case of phosphatidylethanolamine, most arachidonic acid (greater than 90%) was incorporated into the 2-position. PGF2alpha caused the stimulation of arachidonic acid release but not of palmitic acid and linoleic acid from pre-labeled fibroblasts. The serum in the medium was completely replaceable by bovine serum albumin. The effect of PGF2Alpha increased with an increasing concentration of bovine serum albumin, suggesting that serum only acts as a "trap" for released arachidonic acid. The effect of PGF2Alpha was greater than bradykinin, and no synergistic effect was seen, although an additive effect was observed. The effect of PGF2Alpha depended on the concentration of calcium ions under magnesium-supplemented conditions.     

Chronic regulation by thyrotropin of arachidonic acid incorporation in cholesteryl esters of cultured thyroid cells

During short term incubations, radioactive arachidonic acid and palmitic acid were incorporated in the cholesteryl ester fraction of the lipids of cultured thyroid cells. Three times more arachidonic than palmitic acid was incorporated and the incorporation of both was dependent upon the culture conditions: the presence of 1 mU/ml thyrotropin in the culture medium during four days almost completely inhibited the subsequent incorporation of the two fatty acids in the cholesteryl ester fraction whereas the total cholesterol and cholesteryl ester content of the cells was not affected.     

Effect of 7 beta-hydroxycholesterol on growth and membrane composition of Mycoplasma capricolum

7 beta-OH cholesterol in a cholesterol rich growth medium (5-10 micrograms/ml) extended the lag period and slowed down the growth rate of Mycoplasma capricolum cells. In a cholesterol poor medium (0.5 micrograms/ml) inadequate to support growth, 7 beta-OH cholesterol exerts a synergistic effect on growth. The 7 beta-OH cholesterol was incorporated unchanged from the growth medium and could be recovered exclusively in the membrane fraction. The incorporation of the 7 beta-OH cholesterol has no effect on the total phospholipid content but the DPG to PG ratio was markedly decreased. Exchange studies with lipid vesicles revealed that whereas most of the cholesterol underwent exchange, only about 20% of the 7 beta-OH cholesterol was exchanged.     

Lipid composition and lipid metabolism of Spiroplasma citri.

In a horse serum-based medium containing a full complement of fatty acids, cells of Spiroplasma citri were seen to preferentially incorporate palmitic acid. In the same medium, which had a steryl ester-to-sterol ratio of 3.64, a steryl ester-to-sterol ratio of 0.23 was seen in the cells, cholesterol being preferentially incorporated over cholesteryl ester. Like most other mycoplasmas, S. citri was shown to be unable to synthesize fatty acids or esterify cholesterol. The neutral lipids of S. citri grown in a medium containing horse serum consisted of free cholesterol, cholesteryl ester, free fatty acids, triglycerides and diglycerides. All polar lipids were phospholipids, with no glycolipids detected. These phospholipids, which are characteristic of many mycoplasmas, are phosphatidyl glycerol, diphosphatidyl glycerol, and their lyso derivatives. Sphingomyelin was also incorporated when cells were grown on horse serum. A sterol requirement for the growth of S. citri was confirmed using a serum-free medium supplemented with bovine serum albumin, palmitic acid, and various concentrations of sterols dissolved in Tween 80. The addition of palmitic acid stimulated growth but was not essential for growth. S citri was shown to grow best on cholesterol and beta-sitosterol and was able to grow on stigmasterol and ergosterol to a lesser degree. No growth was obtained using mevalonate, deoxycholate, or taurodeoxycholate as an alternative to sterol. S. citri was also able to grow when palmitic acid was replaced with oleic acid, linoleic acid, or linolenic acid. Alterations in the lipid composition of the growth medium and hence in the lipid composition of S. citri induced changes in the characteristic helical morphology of the cells, concurrent with loss of cell viability. Culture, age, and pH were also factors in determining cell morphology and viability.     

Kinetic profile of the cellular lipid composition in an oleaginous Yarrowia lipolytica capable of producing a cocoa-butter substitute from industrial fats

Cell growth, lipid accumulation and cellular lipid composition of Yarrowia lipolytica growing on mixtures of industrial fats containing stearic, oleic, linoleic and palmitic acid have been studied. During growth, the strain incorporated oleic and linoleic acids more rapidly than the saturated fatty acids. Relatively high lipid accumulation (up to 0.44 g of lipids per g of dry matter) was observed when stearic acid was included in the culture medium. In contrast, substrates rich in oleic acid did not favor cellular lipid accumulation. The accumulated lipids, mainly composed of triacylglycerols (45-55% w/w), demonstrated a different total fatty acid composition compared with that of the substrate; in all cases, the microorganism showed the unusual capacity to increase its cellular stearic acid level, even if this fatty acid was not found in high concentrations in the substrate. This permitted the synthesis of interesting lipid profiles with high percentages of stearic acid and non-negligible percentages of palmitic and oleic acid, with a composition resembling that of cocoa-butter.     

Changes in oleic acid oxidation and incorporation into lipids of differentiating L6 myoblasts cultured in normal or fatty acid-supplemented growth medium.

L6 myoblasts accumulate large stores of neutral lipid (predominantly triacylglycerol) when cultured in fatty acid-supplemented growth medium. No accumulation of neutral lipid was evident in myotubes (differentiated myoblasts) when treated similarly. Triacylglycerol accumulation was rapid and dependent on exogenous fatty acid concentration. Triacylglycerol content in myoblasts cultured in fatty acid-supplemented growth medium was approx. 3-fold higher than that in myotubes treated similarly and 2-3-fold higher than that in myoblasts cultured in normal growth medium. Incorporation studies using [I-14C]oleic acid showed that myoblasts and myotubes take up exogenous fatty acid at similar rates. However, cells cultured in fatty acid-supplemented growth medium remove more exogenous fatty acid than do cells cultured in normal growth medium. Over 90% of the incorporated label was found in phospholipid and triacylglycerol fractions in all situations studied. Myoblasts incorporated a more significant proportion (P less than 0.001) of label into triacylglycerol compared with that of myotubes. No differences in fatty acid oxidation rates were detected when differentiating L6 cells cultured in normal growth medium were compared with those cultured in fatty acid-supplemented growth medium. However, fatty acid oxidation rates were observed to increase 3-5-fold upon myoblast differentiation. We conclude that there is a marked change in the pattern of lipid metabolism when myoblasts (primarily triacylglycerol-synthesizing cells) differentiate into myotubes (primarily phospholipid-synthesizing cells). Understanding these changes, which coincide with normal muscle development, may be important, since a defect in this natural switch could explain the observed accumulation of lipid in muscle characteristic of some of the muscular dystrophies and other lipid-storage myopathies.     

Ethynylestradiol alters lipid composition and phosphatidylethanolamine metabolism in red blood cells

Treatment of female rats with ethinylestradiol at a dose of 60 micrograms/rat, daily for 21 days, produced marked changes in red blood cell lipids. Cholesterol was decreased by 22% and total phospholipids were increased by 13%, resulting in a 31% decrease in the cholesterol to phospholipid ratio. The mass distribution of phosphatidylcholine and phosphatidylethanolamine relative to total phospholipids was unchanged. Whereas control red cells incorporated preferentially fatty acids in phosphatidylcholine, ethinylestradiol stimulated their incorporation specifically in phosphatidylethanolamine, where increases occurred with palmitic acid (+75%), oleic acid (+68%) and arachidonic acid (+31%). Incorporation in phosphatidylcholine was unaffected with any of the 3 fatty acids. The stimulation of fatty acid incorporation in phosphatidylethanolamine is likely to reflect an estrogen-dependent increase in turnover rate of fatty acids in this phospholipid. Such alterations in lipid composition and fatty acid incorporation in red cell phospholipids may have significant effects on membrane function.     

Diphosphatidylglycerol in experimental acute alveolar injury in the dog

Acute alveolar injury closely resembling that seen in humans was induced in dogs by subcutaneous injection of N-nitroso-N-methylurethane. Necrosis of alveolar epithelial cells was observed during early injury. Proliferation of immature epithelial cells which began during early injury and became massive after peak injury was followed by their differentiation to mature type II cells during recovery. Quantities of diphosphatidylglycerol (DPG) and of phosphatidylglycerol (PG) in alveolar lavage and in post-lavage lung tissue were measured. An increase in tissue DPG coincided with a sharp decrease in tissue and lavage PG during early injury. DPG was not detectable in the lavage. During late recovery, tissue DPG increased threefold over controls. This increase was accompanied by persistence of a 50% decrease in tissue PG and 83% decrease in lavage PG. Biosynthesis of DPG and PG in isolated lung mitochondria demonstrated that DPG was formed from PG in the presence of CDP-diglyceride. These findings suggest that the low level of PG in the surfactant complex during acute alveolar injury is due to increased turnover of PG to DPG in the lung.