Correction of abnormal lipid fluidity and composition of rat ileal microvillus membranes in chronic streptozotocin-induced diabetes by insulin therapy

Diabetes was induced in rats by administration of streptozotocin. After 90-120 days, one group of chronic diabetic animals was treated with insulin for chronic diabetic animals was treated with insulin for 10 days. The lipid fluidity and composition of microvillus membranes prepared from ileal enterocytes of control, diabetic, and insulin-treated diabetic animals were determined. Lipid fluidity, as assessed by steady-state fluorescence polarization techniques using the probes 1,6-diphenyl-1,3,5-hexatriene, DL-2-(9-anthroyl)stearic acid and DL-12-(9-anthroyl)stearic acid, was decreased in membranes of diabetic animals compared to membranes of control and insulin-treated diabetic membranes. The differences in fluidity resulted from an increased cholesterol content and cholesterol/phospholipid molar ratio in membranes of diabetic animals. The activities of sucrase and alkaline phosphatase were also found to be higher in membranes of diabetic animals. Insulin treatment, however, failed to significantly influence the enzymatic activities of these membranes. These studies, therefore, demonstrate that alterations in the lipid fluidity, lipid composition, and certain enzymatic activities exist in microvillus membranes of enterocytes prepared from chronic streptozotocin-induced diabetic rats. Administration of insulin for 10 days to these animals restored membrane fluidity and lipid composition but not enzymatic activities to control membrane levels.     

Lipid fluidity and composition of intestinal microvillus membranes isolated from rats of different ages

The lipid composition and fluidity of microvillus (luminal) membranes isolated from the small intestines of Fisher 344 rats aged 6, 17, and 117 weeks were compared. Lipid fluidity, as assessed by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene, was significantly greater in rats aged 6 weeks as compared to 17 or 117 weeks. A lipid thermotropic transition was observed at 17.5 +/- 1.3 degrees C in the membranes of the youngest group, approx. 5-6 degrees C lower than that of the older animals. The differences in lipid composition which account for the higher fluidity of the youngest preparations include a decreased cholesterol/phospholipid molar ratio in both the proximal and distal halves of the small intestine and, in the proximal half alone, increases in the lipid/protein ratio and double bond index. The foregoing reduction in cholesterol/phospholipid ratio derives mainly from a higher content of total phospholipid, and the increment in double bond index results from an increase in arachidonic acid residues. The results demonstrate an age-dependent decrease in fluidity of intestinal microvillus membranes in the early post-weaning period in the rat. This pattern was unlike that of the microvillus membrane p-nitrophenylphosphatase, whose specific activity declined progressively in the older age groups.     

Variations in dietary triacylglycerol saturation alter the lipid composition and fluidity of rat intestinal plasma membranes

Rats were maintained on nutritionally complete diets enriched in unsaturated (corn oil) or saturated (butter fat) triacylglycerols. After 6 weeks, significant differences in the lipid composition and fluidity of a number of intestinal membranes were observed. The corn oil diet (enriched mainly in linoleic acid) increased the overall unsaturation of the acyl chains and enhanced the lipid fluidity, as assessed by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene, of enterocyte microvillus and basolateral membranes and of colonocyte basolateral membranes. Concomitantly, the cholesterol content and the cholesterol/phospholipid molar ratio were increased in the microvillus but not in the basolateral membranes. The increased cholesterol in ileal microvillus membranes can result from enhanced cellular biosynthesis, since ileal slices from rats fed the unsaturated diet incorporated [14C]octanoate more rapidly into digitonin-precipitable sterol. Increased fluidity of the enterocyte microvillus and basolateral membranes, respectively, enhanced the enzyme specific activities of p-nitrophenylphosphatase and (Na+ + K+)-dependent adenosine triphosphatase. The results indicate that the lipid composition, fluidity and enzyme activities of intestinal plasma membranes can be altered by dietary means. Moreover, rat enterocytes possess regulatory mechanisms which modulate the cholesterol content of the microvillus membranes so as to mitigate changes in lipid fluidity.     

Regional differences in the lipid composition and fluidity of rat colonic brush-border membranes

The lipid composition and fluidity of brush-border membranes prepared from rat proximal and distal colonocytes were determined. Fluidity, as assessed by steady-state fluorescence polarization techniques using the fluorophores 1,6-diphenyl-1,3,5-hexatriene, DL-2(9-anthroyl)stearic acid and DL-12(9-anthroyl)stearic acid, was decreased in distal compared to proximal plasma membranes. This pattern was similar to that previously described for both antipodal plasma membranes in rat enterocytes of the small intestine. The decrease in fluidity of the distal as compared to the proximal membranes resulted from an increase in cholesterol content, cholesterol/phospholipid molar ratio and degree of saturation of the fatty acid residues in the distal membranes. The specific activities of total alkaline phosphatase and cysteine-sensitive alkaline phosphatase, enzymes previously shown to be functionally dependent on the physical state of the colonic brush-border membrane's lipid, were also significantly lower in distal as compared to proximal clonic plasma membranes. These studies, therefore, demonstrate that differences in the lipid fluidity, lipid composition and certain enzymatic activities exist in brush-border membranes prepared from rat proximal and distal colonocytes. The regional variation in rat colonic luminal membrane lipid fluidity and composition may, at least partially, be responsible for differences in these enzymatic activities as well as in sodium and water absorption along the length of this organ.     

Effects of ethinyl estradiol on intestinal membrane structure and function in the rabbit

Structural and functional properties of the small intestinal microvillus membrane were evaluated in the rabbit after administration of ethinyl estradiol, a synthetic estrogen with a demonstrated propensity to alter hepatic membrane lipid fluidity, and promote cholestasis. In the jejunum, no estrogen-induced changes in microvillus membrane total lipid, cholesterol or phospholipid content were observed. However, the ileal microvillus membrane in estradiol-treated animals demonstrates significant reductions vs. controls (per mg protein) in total lipid (0.55 milligrams vs. 0.89 milligrams) [corrected] and phospholipid (206.7 micrograms vs. 304.91 micrograms) (p less than 0.001) content, as well as modifications in specific phospholipid species. The increase in the ileal microvillus membrane cholesterol: phospholipid molar ratio (0.65 vs. 0.51, p less than 0.05) was associated with a significant decrease in membrane lipid fluidity reflected by an increase in fluorescence anisotropy measurements utilizing diphenyl hexatriene as the fluorophore (r at 25 degrees C = 0.306 vs. 0.282, p less than 0.05). Thermotropic lipid phase transitions, assessed by Arrhenius plots of both fluorescence data and ileal microvillus membrane p-nitrophenylphosphatase activity demonstrate that phase changes occur between and 24 and 28 degrees C in both treated and untreated groups. Within the temperature range studied (40-10 degrees C) no differences from control were observed in microvillus membrane alkaline phosphatase activity following estrogen treatment. These data therefore indicate that ethinyl estradiol-induced effects on microvillus membrane lipid composition and physical properties occur predominantly in the ileum and appear to be related, in part, to specific alterations in the availability of phospholipid following estrogen treatment.     

Two pools of cholesterol in acetylcholine receptor-rich membranes from Torpedo

The acetylcholine receptor (AChR)-containing electroplax membranes from Torpedo californica have a relatively high cholesterol content. Reconstitution studies suggest that this cholesterol may be important in preserving or modulating the function of the acetylcholine receptor-channel complex. We have manipulated cholesterol levels in intact Torpedo AChR-rich membrane fragments using small, unilamellar phosphatidylcholine liposomes. Conditions have been established that allow further subfractionation of sucrose gradient purified Torpedo electroplax membranes into AChR-rich and ATPase-rich populations and that, at the same time, achieve cholesterol depletion without phospholipid back exchange or fusion. The incubation of membranes with excess liposomes could only achieve about a 50% reduction in the molar ratio of cholesterol to phospholipid. In no case was the number of cholesterol molecules per AChR oligomer reduced below 36. The remaining cholesterol could not be depleted either by longer incubations or by multiple, sequential depletions. Cholesterol depletion was accompanied by a significant increase in bulk membrane fluidity as measured by electron spin resonance spectroscopy, but the equilibrium binding parameters of acetylcholine to its receptor were unaltered. This suggests strongly that there exist two pools of cholesterol in the AChR-rich Torpedo electroplax membrane: an easily depleted fraction that influences bulk fluidity, and a tightly-bound fraction perhaps surrounding the AChR oligomer.     

Isolation from neutrophil membranes of a complex containing active NADPH oxidase and cytochrome b-245

The lipid composition and fluidity of basolateral membranes prepared from the mucosa of the proximal, middle and distal thirds of the rat small intestine were determined. Fluidity, as assessed by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene and a series of anthroyloxy fatty acid derivatives, is decreased in the distal third as compared to the proximal segments. This pattern is similar to that described previously for microvillus membranes. The decrease in fluidity of the distal as compared to the proximal membranes results from an increase in cholesterol content, cholesterol/phospholipid molar ratio and degree of saturation of the fatty acid residues. In the middle and distal thirds of the gut, the degree of saturation of the fatty acid residues is higher in microvillus as compared to basolateral membranes, accounting in part for the characteristically lower fluidity of the luminal membranes. The specific activity of the basolateral membrane (Na+ + K+)-dependent adenosine triphosphatase is significantly lower in the distal as compared to the proximal and middle thirds of the intestinal mucosa. Studies of the binding of [3H]ouabain indicate that this pattern results from fewer enzyme sites in the distal membranes.     

Lipid composition of the isolated rat intestinal microvillus membrane

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

Interactions of cholesterol hemisuccinate with phospholipids and (Ca2+-Mg2+)-ATPase

Cholesterol hemisuccinate has been shown to equilibrate readily with liposomes and with the (Ca2+-Mg2+)-ATPase from sarcoplasmic reticulum and has been used to modify the sterol content of these membranes. Cholesterol hemisuccinate incorporates into dioleoylphosphatidylcholine (DOPC) up to a molar ratio of 3:1 sterol to DOPC. Effects on lipid order as detected by electron spin resonance and fluorescence polarization are comparable to those of cholesterol. Binding constants have been determined, and the uncharged form of the sterol binds more strongly than the anionic form. Binding to DOPC and to the lipid component of the ATPase system is comparable. From use of the fluorescence quenching properties of 1,2-bis(9,10- dibromooleoyl )phosphatidylcholine and dibromocholesterol hemisuccinate, two classes of binding sites on the ATPase have been deduced. At the lipid/protein interface, the binding constant for cholesterol hemisuccinate is considerably less than that for DOPC. At the second set of sites ( nonannular sites), binding occurs with Kd = 0.55 in molar ratio units. The effect of cholesterol hemisuccinate on the activity of the ATPase depends on the phospholipid present in the system: ATPase reconstituted with DOPC is inhibited whereas ATPase reconstituted with dimyristoleoylphosphatidylcholine is activated. We conclude that changes in membrane fluidity are not important in determining ATPase activity in these systems.     

Lipid composition and fluidity of rat enterocyte basolateral membranes regional differences

The lipid composition and fluidity of basolateral membranes prepared from the mucosa of the proximal, middle and distal thirds of the rat small intestine were determined. Fluidity, as assessed by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene and a series of anthroyloxy fatty acid derivatives, is decreased in the distal third as compared to the proximal segments. This pattern is similar to that described previously for microvillus membranes. The decrease in fluidity of the distal as compared to the proximal membranes results from an increase in cholesterol content, cholesterol/phospholipid molar ratio and degree of saturation of the fatty acid residues. In the middle and distal thirds of the gut, the degree of saturation of the fatty acid residues is higher in microvillus as compared to basolateral membranes, accounting in part for the characteristically lower fluidity of the luminal membranes. The specific activity of the basolateral membrane (Na⁺ + K⁺)-dependent adenosine triphosphatase is significantly lower in the distal as compared to the proximal and middle thirds of the intestinal mucosa. Studies of the binding of [³H]ouabain indicate that this pattern results from fewer enzyme sites in the distal membranes.     

Modulation of sarcoplasmic reticulum Ca2+-pump activity by membrane fluidity

Intramolecular excimerization of 1,3-di-1-pyrenylpropane [Py(3)Py] was used to assess the fluidity of sarcoplasmic reticulum membranes (SR); on the basis of the spectral data, the probe incorporates completely inside the membrane probably somewhere close to the polar head groups of phospholipid molecules, however not in the very hydrophobic core. The excimerization rate is very sensitive to lipid phase transitions, as revealed by thermal profiles of dimyristoyl-phosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) bilayers. Cholesterol abolishes pretransitions and broadens the thermal profiles of the main transitions which vanish completely at 50 mol % sterol. Excimer formation in liposomes of SR total lipid extracts does not show any sharp transitions, as in the case of DMPC and DPPC. However, the plots display discontinuities at about 20 degrees C which are broadened by cholesterol and not observed at 50 mol % sterol. Also cholesterol has been incorporated in native SR membranes by an exchange technique allowing progressive enrichment without changing the phospholipid/protein molar ratio. As in liposomes, discontinuities of excimer formation at 20 degrees C are broadened by cholesterol enrichment. The full activity of uncoupled Ca2+-ATPase is only affected by cholesterol above a molar ratio to phospholipid of 0.4. However, a significant decrease in activity (about 20%) is only noticed at a ratio of 0.6 (the highest technically achieved); at this ratio, about 28 lipid molecules per Ca2+-ATPase are expected to be relatively free from cholesterol interaction. The vesicle structure is still intact at this high ratio, as judged from the absence of basal activity (not Ca2+ stimulated).(ABSTRACT TRUNCATED AT 250 WORDS)     

Characteristics and physiological role of surfactant-like particles secreted by entrocytes

Intestinal epithelium secretes novel unilamellar membranes having characteristics similar to lung surfactants and thus has been named Surfactant-like particles (SLP). The chemical analysis of the membranes revealed cholesterol/phospholipid molar ratio of 0.68-0.78, which is much distinct from that of the underlying microvillus membranes (1.34-1.49). The membrane contains 4-6 proteins with a molar weight of 30-120 kDa and is enriched with alkaline phosphatase, contains low amounts of disaccharidases but no Na+, K(+)-ATPase activity. The secretion of SLP is stimulated by fat feeding. Chronic ethanol ingestion also induces the formation of SLP in rat intestine. A number of physiological functions have been attributed to SLP, which include: (i) as a protective lubricant in intestinal lumen, (ii) a role in triacylglycerol transport, (iii) as a vehicle for the transport of luminal proteins into blood, (iv) as a stratum for the adhesion of microorganisms in intestinal lumen, and (v) a role in trans-signalling mechanism across the basolateral surface of enterocytes.     

Isolation and characterization of brush-border membrane from trout intestine. Regional differences

The isolation of brush-border membranes from trout enterocytes is described for both middle and posterior intestine. Both procedures are based on differential centrifugations combined with calcium precipitation. Classical marker enzymes are quantified and indicate a valuable purification of the membranes (13-18-fold). No difference appears when comparing the relative amounts of phospholipids, cholesterol and proteins in microvillus membranes isolated from either middle or posterior intestine. In contrast, the membranes isolated from middle intestine are more unsaturated than those from the posterior one, and their sphingomyelin/phosphatidylcholine ratio is lower. These differences are reflected by fluorescence anisotropy studies with diphenylhexatriene as lipid fluorophore which indicate a higher fluidity of the microvillus membranes from the middle intestine as compared with those from the posterior intestine. These results point out the importance of the fatty acyl chains and that of the relative amounts of phosphatidylcholine and sphingomyelin in controlling the fluidity of biological membranes in relation with their transport properties.     

Galactose effects on enterocyte differentiation in the mouse jejunum

The present work investigates the ability of galactose to affect enterocyte differentiation during normal development in vivo. Energy intake has also been varied to take account of the fact that galactose is poorly metabolized in mice. Brush-border lactase, alpha-glucosidase, dipeptidylpeptidase-IV, aminopeptidase N, alkaline phosphatase and microvillus length were measured as markers of enterocyte differentiation in mice fed diets containing galactose (G diet), corn oil (E diet) or galactose + corn oil (G + E diet). Maintaining mice on a G instead of E diet reduced brush-border lactase activity and enterocyte migration rates; alpha-glucosidase, dipeptidylpeptidase-IV, aminopeptidase N and microvillus length expression increased and alkaline phosphatase activity remained unchanged. Feeding the G + E diet restored enterocyte migration rates, lactase, aminopeptidase N and dipeptidylpeptidase-IV activities to values found in mice fed the E diet. Galactose stimulation of alpha-glucosidase and microvillus length expression was, however, fully maintained in mice fed the G + E diet. Present results show that enterocyte differentiation is affected independently by varying dietary galactose and energy levels; that galactose effects always increase and energy effects usually decrease expression of enterocyte components and that energy stimulation of lactase activity is exceptional.     

Fluidity and lipid composition of oat and rye shoot plasma membrane: effect of sterol perturbation by xenobiotics

Oat and rye plants were treated with either tetcyclacis (an experimental plant growth regulator), nuarimol (a fungicide) or gamma-ketotriazole (an experimental herbicide). These treatments reduced shoot growth and changed the lipid composition of the shoot plasma membranes. In oat, both tetcyclacis and nuarimol treatments increased plasma membrane cholesterol and increased the phosphatidylethanolamine/phosphatidylcholine (PE/PC) ratio, whereas gamma-ketotriazole treatment reduced cholesterol and the PE/PC ratio. In rye, all treatments reduced the PE/PC ratio. Generally, the sterol/phospholipid ratio was less in oat than in rye but the cholesterol/phospholipid ratio was greater. With all treatments in oat and rye, increases were observed in unsaturation of the phospholipid acyl chains. The fluidity of membranes was measured by steady-state fluorescence polarisation of the probe diphenylhexatriene; oat membranes were more fluid than rye. Membrane fluidity was greater in plasma membranes from plants treated with the xenobiotics than the controls. The results are discussed in the context of the effect of plasma membrane lipid composition on membrane fluidity, and it is concluded that there appears to be no overall simple relationship between membrane lipid composition and fluidity that holds for all treatments in both species.     

Structural alterations of the inner mitochondrial membrane in ischemic liver cell injury

Mitoplasts were prepared from 3-h ischemic livers in an attempt to define the structural alterations in the inner membrane that may account for the functional deficiencies of ischemic mitochondria. Mitoplasts from both control and ischemic livers had similar specific activities of cytochrome oxidase and succinate-cytochrome c reductase. With both preparations, the specific activity of rotenone-insensitive NADH-cytochrome c reductase was 10-fold lower than in the mitochondria from which they were prepared. Ischemic mitoplasts had no respiratory control with ADP, and had a slightly reduced phospholipid to protein ratio and an increased cholesterol to protein ratio. As a result, the cholesterol to phospholipid molar ratio was increased from the control of 0.04 to 0.08. There were also differences in the content of individual phospholipid species. Phosphatidylcholine increased by 15%, while cardiolipin decreased by 60%. There were increases in sphingomyelin and in the lysophospholipids of phosphatidylcholine, ethanolamine, and cardiolipin. Pretreatment with chlorpromazine did not prevent these changes. Linoleic acid was decreased by 35% in ischemic phospholipids, and the content of free fatty acids was increased 4-fold. Electron spin resonance spectroscopy of mitoplasts spin labeled with either 5- or 12-doxyl stearic acid revealed an increased molecular order (decreased fluidity) of ischemic inner mitochondrial membranes consistent with the increased cholesterol to phospholipid ratio. The data indicate activation of a phospholipase A in ischemic mitochondria with the resulting accumulation of products of lipid hydrolysis. This conclusion further emphasizes the close similarity between the structural and functional consequences of ischemia in the intact animal and the effect on isolated mitochondria of the activation of the endogenous phospholipase A. In both cases the major functional alterations are attributable to changes in the permeability of the inner mitochondrial membrane induced by the accumulation of lysophospholipids.     

The role of sphingomyelin synthetase and sphingomyelinase in 1,2-dimethylhydrazine-induced lipid alterations of rat colonic plasma membranes

Recently, our laboratory, utilizing the 1,2-dimethylhydrazine model of colonic adenocarcinoma, demonstrated alterations in the 'dynamic component' of fluidity in brush-border membranes prepared from distal colonocytes of rats administered this agent for 5, 10 and 15 weeks, i.e., before the development of colon cancer. Furthermore, changes in the sphingomyelin content and sphingomyelin/phosphatidylcholine molar ratio of these membranes appeared, at least partially, to be responsible for these fluidity alterations. In an attempt to elucidate the mechanism(s) involved in these dimethylhydrazine-induced lipid changes, in the present studies the activities of sphingomyelin synthetase and magnesium-dependent neutral sphingomyelinase, enzymes involved in the synthesis and degradation of this phospholipid, respectively, were examined and compared in distal colonic brush-border membranes prepared from rats after 5, 10 or 15 weeks administration of dimethylhydrazine or diluent. The results of these studies demonstrate that alterations in both these enzymatic activities can be detected after administration of dimethylhydrazine and appear to, at least in part, be responsible for the changes in membrane sphingomyelin composition noted previously. These results as well as a discussion of their possible serve as the basis for the present report.     

Cholesterol attenuates and prevents bilayer damage and breakdown in lipoperoxidized model membranes. A spin labeling EPR study

The stabilizing effect of cholesterol on oxidized membranes has been studied in planar phospholipid bilayers and multilamellar 1-palmitoyl-2-linoleoyl-phosphatidylcholine vesicles also containing either 1-palmitoyl-2-glutaroyl-phosphatidylcholine or 1-palmitoyl-2-(13-hydroxy-9,11-octadecanedienoyl)-phosphatidylcholine oxidized phosphatidylcholine in variable ratio. Lipid peroxidation-dependent membrane alterations in the absence and in the presence of cholesterol were analyzed using Electron Paramagnetic Resonance spectroscopy of the model membranes spin labelled with either cholestane spin label (3-DC) or phosphatidylcholine spin label (5-DSPC). Cholesterol, added to lipid mixtures up to 40% final molar ratio, decreased the inner bilayer disorder as compared to cholesterol-free membranes and strongly reduced bilayer alterations brought about by the two oxidized phosphatidylcholine species. Furthermore, Sepharose 4B gel-chromatography and cryo electron microscopy of aqueous suspensions of the lipid mixtures clearly showed that cholesterol is able to counteract the micelle forming tendency of pure 1-palmitoyl-2-glutaroyl-phosphatidylcholine and to sustain multilamellar vesicles formation. It is concluded that membrane cholesterol may exert a beneficial and protective role against bilayer damage caused by oxidized phospholipids formation following reactive oxygen species attack to biomembranes.     

Effect of cholesterol on the branched-chain amino acid transport system of Streptococcus cremoris.

The effect of cholesterol on the activity of the branched-chain amino acid transport system of Streptococcus cremoris was studied in membrane vesicles of S. cremoris fused with liposomes made of egg yolk phosphatidylcholine, soybean phosphatidylethanolamine, and various amounts of cholesterol. Cholesterol reduced both counterflow and proton motive force-driven leucine transport. Kinetic analysis of proton motive force-driven leucine uptake revealed that the Vmax decreased with an increasing cholesterol/phospholipid ratio while the Kt remained unchanged. The leucine transport activity decreased with the membrane fluidity, as determined by steady-state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene incorporated into the fused membranes, suggesting that the membrane fluidity controls the activity of the branched-chain amino acid carrier.     

Changes in phospholipids from chick fibroblasts during embryo development

The content of cholesterol and total phospholipids was assayed in 8- and 16- day old chick embryo fibroblasts, harvested at subconfluence after a 48- and 96-hour primoculture, respectively. Cholesterol content did not change during embryo development, whereas the amount of total phospholipids decreased (28%) from the 8th to the 16th day of development, giving an increase of the cholesterol/phospholipid ratio. Studies of the fatty acid composition of the predominant membrane phospholipids indicated that there was no significant change in phosphatidylcholine, whereas phosphatidylethanolamine was depleted in the myristate, as the embryo grew older. These findings demonstrate that the lipid contents are modified during embryo development and suggest that the fluidity of chick embryo cell membranes decreased during development.