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 the erythrocyte membrane from healthy dogs and labrador retrievers with hereditary muscular dystrophy

Erythrocyte membranes and their liposomes were prepared from clinically normal dogs and Labrador retrievers with hereditary muscular dystrophy. The static and dynamic components of fluidity of each membrane were then assessed by steady-state fluorescence polarization techniques using limiting hindered fluorescence anisotropy and order parameter values of 1,6-diphenyl-1,3,5-hexatriene (DPH) and fluorescence anisotropy values ofdl-2-(9-anthroyl)-stearic acid anddl-12-(9-anthroyl)-stearic acid, respectively. Membrane lipids were extracted and analyzed by thin-layer chromatography and gas chromatography. The results of these studies demonstrated that the lipid fluidity of erythrocyte membranes, and their liposomes, prepared from dystrophic dogs were found to possess significantly lower static and dynamic components of fluidity than control counterparts. Analysis of the composition of membranes from dystrophic dogs revealed a higher ratio of saturated fatty acyl chain/unsaturated chains (w/w) and lower double-bond index. Alterations in the fatty acid composition such as decrease in levels of linoleic (18:2) and arachidonic (20:4) acids and increase in palmitic (16:0) and stearic (18:0) acids were also observed in the membranes of dystrophic animals. These associated fatty acyl alterations could explain, at least in part, the differences in membrane fluidity between dystrophic and control dogs.     

Rat proximal small intestinal Golgi membranes: lipid composition and fluidity

The present studies were conducted to examine and characterize the lipid composition and physical state of the membrane lipids of rat proximal small intestinal Golgi membranes. Golgi membranes were purified from isolated enterocytes; lipids were extracted from these membranes and analyzed by thin-layer and gas-liquid chromatography. The 'static' and 'dynamic' components of fluidity of Golgi membranes and their liposomes were assessed by steady-state fluorescence polarization techniques utilizing r infinity and S values of 1,6-diphenyl-1,3,5-hexatriene and r values of DL-2-(9-anthroyl)- and DL-12-(9-anthroyl)stearic acid, respectively. Additional studies were also performed on these membranes, using benzyl and methyl alcohol, to examine the relationship between alterations in lipid fluidity and glycosphingolipid glycosyltransferase activities. The results of these studies demonstrated that: (1) the principal phospholipids and neutral lipids of intestinal Golgi membranes, respectively, were phosphatidylcholine, phosphatidylethanolamine and sphingomyelin, and unesterified cholesterol and fatty acids; (2) the major fatty acids of Golgi membranes were palmitic (16:0), stearic (18:0), linoleic (18:2), arachidonic (20:4) and oleic (18:1) acids; (3) fluorescence polarization studies using diphenylhexatriene detected a thermotropic transition at 24-26 degrees C in Golgi membranes and liposomes prepared from lipid extracts of these membranes; (4) benzyl alcohol (25 and 50 mM) but not methyl alcohol (50 mM) significantly increased the fluidity of these membranes; and (5) at these same concentrations, benzyl alcohol was also found to increase significantly the specific activity of UDP-galactosyllactosylceramide galactosyltransferase but not CMP-acetylneuraminic acid: lactosylceramide sialyltransferase. Methyl alcohol was not found to influence either enzyme's activity in these membranes.     

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.     

Ontogeny of proximal colon basolateral membrane lipid composition and fluidity in the rabbit.

Basolateral membranes from rabbit proximal colon were prepared from isolated colonocytes throughout postnatal maturation, using a modification of published techniques. In suckling (14-20 day) and post-weaning/mature (35-49 day) animals, membranes were purified approx. 10-fold, based upon the enrichment of ouabain-sensitive, sodium-potassium dependent adenosine triphosphatase activity. Membrane lipid analyses demonstrated age-dependent increases in total cholesterol and the cholesterol/phospholipid molar ratio, as well as decreases in phosphatidylethanolamine content and the fatty acid unsaturation index. Fluidity of basolateral membranes and membrane liposomes, determined from fluorescence anisotropy measurements using the lipid probes 1,6-diphenyl-1,3,5-hexatriene and DL-12-(9-anthroyl)stearic acid, demonstrated significant, ontogenic decreases in fluidity; and, additional studies showed that fluidity changes occurred early in the weaning period (by day 24 postnatally). Arrhenius plots of liposome anisotropies suggested a bilayer lipid thermotropic transition temperature of 22 degrees C in sucklings 26 degrees C in mature rabbits. These findings demonstrate that ontogeny of colonic basolateral membranes is associated with significant modulations in lipid composition and fluidity.     

Liver microsomal membrane fluidity and lipid characteristics in vitamin A-deficient rats.

Rat liver microsomes (microsomal fraction) were isolated from vitamin A-deficient and -sufficient rats and analysed for membrane lipid characteristics. Membrane fluidity was found to be significantly decreased in microsomes from the vitamin A-deficient rats, but not in liposomes prepared from lipid extracts. Microsomes from vitamin A-deficient animals showed a significant decrease in C18:2, omega 6 and an increase in C22:5, omega 6 fatty acids.     

Relationship between vitamin D status and deposition of bound calcium in skeletal muscle of the rat

Summary— The effects of vitamin D on the intramuscular distribution of total and bound calcium, phosphate and on available cytosolic calcium, were investigated in skeletal muscle. Total calcium and phosphorus were measured on ashed subcellular fractions of muscles from vitamin D-repleted and vitamin D-deprived rats. The variations in available calcium were followed by determining the activities of calcium-sensitive enzymes in isolated cytosol. Bound-calcium was revealed ultra-microscopically by pyroantimonate. In vitamin D-repleted muscles, the pyroantimonate method revealed specific areas of intense bound-calcium deposition: the myofibrils, where they formed pronounced lines parallel to the Z-bands. In vitamin D-deficient muscles, the calcium-pyroantimonate deposits appeared clearly reduced. This loss was accompanied by a marked reduction in total calcium and phosphorus in all the subcellular fractions, as compared to vitamin D-repleted muscles. Unexpectedly, the activity of the Ca²⁺-activated isocitrate-dehydrogenase was increased in the cytosol, while that of the Ca²⁺-inhibited pyruvate-kinase decreased. Prolonged vitamin D-administration to vitamin D-repleted rats led to an intensification of calcium-pyroantimonate deposits and a general increase in total calcium and phosphorus, but no change in the cytosolic Ca²⁺-sensitive enzyme activities. Cessation of vitamin D-administration to vitamin D-repleted rats produced a regression of calcium-pyroantimonate deposits, a general decrease of total calcium and phosphate levels, and stimulation of the Ca²⁺-activated isocitrate-dehydrogenase accompanied by lowering of the Ca²⁺-inhibited pyruvate-kinase. The results clearly indicate a correlation between vitamin D-repletion and the total and bound calcium content of skeletal muscle. In addition, they demonstrate an apparent contradiction between the decrease of total and bound calcium, and the activities of cytosolic Ca²⁺ sensitive enzymes during vitamin D-deprivation, which can only be explained by an increase in available calcium. It is suggested that vitamin D stimulates intramuscular mechanisms tending to lower available calcium by inactivating the cation via the formation of calcium chelates.     

Dietary triacylglycerol modulates sodium-dependent D-glucose transport, fluidity and fatty acid composition of rat small intestinal brush-border membrane

Rats were maintained on nutritionally complete diets enriched in unsaturated (menhaden fish oil) or saturated (butter fat) triacylglycerols. After 4 weeks, the animals were killed, proximal small intestinal brush-border membranes were prepared, and examined and compared with respect to their lipid composition, molecular species of phosphatidylcholine, lipid fluidity and sodium-dependent D-glucose transport. Membranes prepared from the two dietary groups were found to possess similar ratios of cholesterol/phospholipid (mol/mol), sphingomyelin/phosphatidylcholine (mol/mol), and protein/lipid (w/w). In contrast to these findings, however, striking differences were noted in the total fatty acid compositions of these membranes. Plasma membranes prepared from animals fed the fish oil diet possessed higher percentages of saturated fatty acids as well as (n - 3) unsaturated fatty acids and lower percentages of monounsaturated and (n - 6) unsaturated fatty acids than those prepared from animals fed the butter fat diet. Analysis of the molecular species of phosphatidylcholine by HPLC, moreover, revealed that membranes from rats fed fish oil had higher levels of 16:0-20:5, 16:0-22:6 and 18:0-20:5 and lower levels of 18:0-18:2 and 16:0-18:1 than their butter fat counterparts. As assessed by steady-state fluorescence polarization, differential polarized phase fluorometric and excimer/monomer fluorescence intensity techniques using various fluorophores, the lipid fluidity of membranes from rats fed fish oil was also found to be significantly lower compared to membranes from rats fed butter fat. Finally, comparison of the kinetic parameters of Na+-dependent D-glucose transport revealed that fish oil-membrane vesicles had a higher maximum velocity (Vmax) than butter fat membrane vesicles but a similar Km for glucose.     

Response of rat heart membranes and associated ion-transporting ATPases to dietary lipid

The effects of different dietary fat intake on the lipid composition and enzyme behaviour of sarcolemmal (Na+ + K+)ATPase and sarcoplasmic reticulum Ca2+-ATPase from rat heart were investigated. Rat diets were supplemented with either sunflower seed oil (unsatd./satd. 5.6) or sheep kidney fat (unsatd./satd. 0.8). Significant changes in the phospholipid fatty acid composition were observed in both membranes after 9 weeks dietary lipid treatment. For both membranes, the total saturated/unsaturated fatty acid levels were unaffected by the dietary lipid treatment, however the proportions of the major unsaturated fatty acids were altered. Animals fed the sunflower seed oil diet exhibited an increase in n-6 fatty acids, including linoleic (18:2(n-6] and arachidonic (20:4(n-6] while the sheep kidney fat dietary rats were higher in n-3 fatty acids, principally docosahexaenoic (22:6), with the net result being a higher n-6/n-3 ratio in the sunflower seed oil group compared to sheep kidney fat dietary animals. Fluorescence polarization indicated that the fluidity of sarcoplasmic reticular membrane was greater than that of sarcolemmal membrane, with a dietary lipid-induced decrease in fluidity being observed in the sarcoplasmic reticular membrane from sheep kidney fat dietary animals. Despite these significant changes in membrane composition and physical properties, neither the specific activity nor the temperature-activity relationship (Arrhenius profile) of the associated ATPases were altered. These results suggest that with regard to the parameters measured in this study, the two ion-transporting ATPases are not modulated by changes which occur in the membrane lipid composition as a result of the diet.     

Effects of fatty acids on the growth of Caco-2 cells

Epidemiological studies suggest that polyunsaturated fatty acids may protect against colorectal neoplasia. In order to explore this observation, cell proliferation and viability, lipid composition, membrane fluidity, and lipid peroxidation were measured in Caco-2 cells after 48h incubation with various fatty acids. Saturated and monounsaturated fatty acids incorporated less well in the membranes than polyunsaturated fatty acids (PUFAs). All of the PUFAs tested had an inhibitory effect on cell proliferation/viability whereas the saturated and monounsaturated fatty acids did not. Addition of palmitic acid had no significant effect on membrane fluidity whereas unsaturated fatty acids increased membrane fluidity in a dose-dependent manner. PUFAs strongly increased tumor cell lipid peroxidation in a dose-dependent manner. Saturated and monounsaturated fatty acids increased lipid peroxidation in this cell line only at high concentration. Preincubation of Caco-2 cells with vitamin E prevented the inhibition of proliferation/viability, the elevation of the MDA concentration and the increased membrane fluidity induced by PUFAs. Our data indicate that PUFAs are potent inhibitors of the growth of colon cancer cells in vitro.     

Lipid composition and fluidity in the jejunal brush-border membrane of spontaneously hypertensive rats. Effects on activities of membrane-bound proteins

The lipid composition and fluidity of jejunal brush-border membrane vesicles (BBMV) have been studied in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. The activities of both Na⁺-dependent D-glucose cotransport and Na⁺-H⁺ antiport have also been determined. A significant increase in the level of free cholesterol was observed in jejunal BBMV from SHR compared to WKY rats. Since phospholipid values did not change in either group of animals, a significant enhancement in the free cholesterol/phospholipid ratio was observed in SHR. A decrease in the levels of phosphatidylethanolamine together with an increase in the values of phosphatidylserine was observed in hypertensive rats. Although the content of phosphatidylcholine (PC) and sphingomyelin (SM) was not singificantly altered in SHR, the ratio PC/SM significantly increased in these animals when compared to WKY rats. The major fatty acids present in bursh-border membranes prepared from SHR and WKY rats were palmitic (160), stearic (180), oleic (181, n-9) and linoleic (182, n-6), and the fatty acid composition was not modified by the hypertension. A decreased fluorescence polarization, i.e., increased membrane fluidity, was observed in SHR, which was not correlated to the increased ratio of cholesterol/phospholipid found in the brush-border membrane isolated from these animals. These structural changes found in SHR were associated to an enhancement in both Na⁺-dependent D-glucose transport and Na⁺-H⁺ antiport activity in the jejunal BBMV of SHR.Abbreviations BBMV brush-border membrane vesicles - DPH 1,6-diphenyl-1,3,5-hexatriene - FC free cholesterol - PC phosphatidylcholine - PE phosphatidylethanolamine - PI phosphatidylinositol - PS phosphatidylserine - SM sphingomyelin - SHR spontaneously hypertensive rat - p steady-state fluoroscence polarization - r_s steady-state fluorescence anisotropy - WKY Wistar Kyoto     

Influence of dietary lipids on microsomal membranes from chick breast muscle

1. The effect of different dietary fat intake on the lipid composition and fluidity of microsomal membranes as well as in the enzymatic activity of the Ca2+-ATPase from chick breast muscle was investigated. 2. When a standard diet was supplemented with 10% sunflower seed oil, an increase in the relative amounts of unsaturated fatty acids and membrane fluidity and a decrease in the cholesterol content was observed. 3. The presence of 6% cholesterol in the diet does not modify the fatty acid composition and the fluidity of the membrane but increased, in a low extension, the cholesterol content. 4. The provision of the sunflower seed oil-rich diet supplemented with cholesterol just 48 hr before death promoted an increase in the relative amounts of unsaturated fatty acids and cholesterol content whereas the membrane fluidity decreased in a significant extent. 5. Despite that dietary lipids gave rise in some cases to changes in lipid composition and in the physical state of the microsomal membrane, neither the Ca2+ uptake capacity nor the ATPase activity were significantly affected.     

Alterations in lipid composition and fluidity of liver plasma membranes in copper-deficient rats

In view of the importance of membrane fluidity on cell functions, the influence of phospholipid acyl groups on membrane fluidity, and the changes in lipid metabolism induced by copper (Cu) deficiency, this study was designed to examine the influence of dietary Cu on the lipid composition and fluidity of liver plasma membranes. Male Sprague-Dawley rats were divided into two dietary treatments, namely Cu deficient and Cu adequate. After 8 weeks of treatment, liver plasma membranes were isolated by sucrose density gradient centrifugation. The lipid fluidity of plasma membranes, as assessed by the intramolecular eximer fluorescence of 1,3-di(1-pyrenyl) propane, was significantly depressed by Cu deficiency. In addition, Cu deficiency significantly reduced the content of arachidonic and palmitoleic acids but increased the docosatetraenoic and docosahexaenoic acids of membrane phospholipids. This alteration in unsaturated phospholipid fatty acid composition, especially the large reduction in arachidonic acid, may have contributed to the depressed membrane fluidity. Furthermore, Cu deficiency also markedly altered the fatty acid composition of the triacylglycerols associated with the plasma membranes. Thus, the lipid composition and fluidity of liver plasma membranes are responsive to the animal's Cu status.     

Changes in cerebral membrane lipid composition and fluidity during thioacetamide-induced hepatic encephalopathy

Lipids are an essential structural and functional component of cellular membranes. Changes in membrane lipid composition are known to affect the activities of many membrane-associated enzymes, endocytosis, exocytosis, membrane fusion and neurotransmitter uptake, and have been implicated in the pathophysiology of many neurodegenerative disorders. In the present study, we investigated changes in the lipid composition of membranes isolated from the cerebral cortex of rats treated with thioacetamide (TAA), a hepatotoxin that induces fulminant hepatic failure (FHF) and thereon hepatic encephalopathy (HE). HE refers to acute neuropsychiatric changes accompanying FHF. The estimation of membrane phospholipids, cholesterol and fatty acid content in cerebral cortex membranes from TAA-treated rats revealed a decrease in cholesterol, phosphatidylserine, sphingomyelin, a monounsaturated fatty acid, namely oleic acid, and the polyunsaturated fatty acids gamma-linolenic acid, decosa hexanoic acid and arachidonic acid compared with controls. Assessment of membrane fluidity with pyrene, 1,6-diphenyl-1,3,5-hexatriene and 1-[4-(trimethylammonio)phenyl]-6-phenyl-1,3,5-hexatriene revealed a decrease in the annular membrane fluidity, whereas the global fluidity was unaffected. The level of the thiobarbituric acid reactive species marker for lipid peroxidation also increased in membranes from TAA-treated rats, thereby indicating the prevalence of oxidative stress. Results from the present study demonstrate gross alterations in cerebral cortical membrane lipid composition and fluidity during TAA-induced HE, and their possible implications in the pathogenesis of this condition are also discussed.     

Evaluation of hydralazine and procainamide effects on fibroblast membrane fluidity

In this study the membrane fluidity of fibroblasts under different pharmacological treatment was investigated. Two drugs, hydralazine and procainamide, were used to treat the immortalized mouse NIH 3T3 and hamster B14 fibroblasts. Membrane lipid dynamics was measured by fluorescence spectroscopy and electron spin resonance techniques. Two kinds of fluorescent probes (TMA-DPH and 12-(9-anthroyloxy)-stearic acid (12-AS)) and two spin labels (5-doxylstearic acid (5-DS) and 12-doxylstearic acid (12-DS)) were used to monitor fluidity in the upper polar and in the hydrophobic core regions of the lipid bilayer. The drugs influenced the membrane hydrophobic core, of which hydralazine induced fluidization and procainamide increased the rigidity. The membrane fluidity at the surface of the lipid bilayer was not modified by the drugs which indicates that both drugs intercalated mainly into the inner core of the cell membrane.     

1,2-Dimethylhydrazine-induced premalignant alterations in the S-adenosylmethionine/S-adenosylhomocysteine ratio and membrane lipid lateral diffusion of the rat distal colon

Prior studies by our laboratory, utilizing the 1,2-dimethylhydrazine experimental model of colonic cancer, had shown that administration of this procarcinogen for 5 weeks was found to increase phospholipid methyltransferase activity and the fluidity of rat distal colonic brush-border membranes. The present studies were conducted to further explore these 'premalignant' colonic phenomena. Male albino rats of the Sherman strain were subcutaneously injected with dimethylhydrazine (20 mg/kg body weight per week) or diluent for 5 weeks. Animals from each group were killed, distal colonic tissue harvested and the levels of S-adenosylmethionine, S-adenosylhomocysteine and decarboxylated S-adenosylmethionine measured by high performance liquid chromatography. The activity of methionine adenosyltransferase was also examined in these tissues. Additionally, brush-border membranes were isolated from the distal colonocytes of control and treated-animals and examined and compared with respect to their phospholipid methylation activities as well as their lipid fluidity as assessed by the rotational mobilities of the probes 1,6-diphenyl-1,3,5-hexatriene and DL-12-(9-anthroyl)stearic acid and translational mobility of the fluorophore pyrenedecanoic acid. The results of these studies demonstrated: (1) phospholipid methyltransferase activity in rat colonic plasma membranes was increased concomitantly with increases in the cellular levels of S-adenosylmethionine and the S-adenosylmethionine/S-adenosylhomocysteine ratio in the distal colonic segment of treated-animals; and (2) the lateral diffusion of rat distal colonic brush-border membrane lipids, as assessed by the ratio of excimer/monomer fluorescence intensities of the fluorophore pyrenedecanoate, was also increased after dimethylhydrazine administration to these animals for 5 weeks.     

Anti-lipoperoxidation action of food restriction

Chronic food restriction inhibited the age-related increase of malondialdehyde production and lipid hydroperoxides in liver mitochondrial and microsomal membranes of ad libitum fed Fischer 344 rats. The anti-lipoperoxidation action of food restriction could not be attributable to the changes in membrane lipid content nor vitamin E status. Restricting calories modified membrane fatty acid composition by increasing linoleic acid and decreasing docosapentaenoic acid content in both membranes. The significance of the fatty acid modification was discussed in terms of anti-lipoperoxidation and membrane fluidity.     

Influence of dietary partially hydrogenated fat high in trans fatty acids on lipid composition and function of intestinal brush border membrane in rats

The effect of dietary hydrogenated fat (Indian vanaspati) high in trans fatty acids (6 en%) on lipid composition, fluidity and function of rat intestinal brush border membrane was studied at 2 and 8 en% of linoleic acid. Three groups of weanling rats were fed rice-pulse based diet containing 10% fat over a ten week period: Group I (groundnut oil), Group II (vanaspati), Group III (vanaspati + safflower oil). The functionality of the brush border membrane was assessed by the activity of membrane bound enzymes and transport of D-glucose and L-leucine. The levels of total cholesterol and phospholipids were similar in all groups. The data on fatty acid composition of membrane phospholipids showed that, at 2 en% of linoleic acid in the diet, trans fatty acids lowered arachidonic acid and increased linoleic acid contents indicating altered polyunsaturated fatty acid metabolism. Alkaline phosphatase activity was increased while the activities of sucrase, gamma-glutamyl transpeptidase and transport of D-glucose and L-leucine were not altered by dietary trans fatty acids. However at higher intake of linoleic acid in the diet, trans fatty acids have no effect on polyunsaturated fatty acid composition and alkaline phosphatase activity of intestinal brush border membrane. These data suggest that feeding dietary fat high in trans fatty acids is associated with alteration in intestinal brush border membrane polyunsaturated fatty acid composition and alkaline phosphatase activity only when the dietary linoleic acid is low.     

Thyroid hormones control lipid composition and membrane fluidity of skeletal muscle sarcolemma.

Sarcolemma membrane lipid phase of skeletal muscles of hyperthyroid animals was compared to that of control (euthyroid) ones. Hyperthyroidism caused 15% decrease in cholesterol and 70% increase in the phospholipid content of the membrane. This was accompanied by the alterations in proportions between individual phospholipid classes, and was followed by changes in the composition of phospholipid fatty acids. The calculated fatty acid unsaturation index was higher for membrane lipid phase of hyperthyroid animals than of euthyroid ones. Thyroxine-induced alterations in the lipid composition of sarcolemma caused changes in the membrane fluidity and the activity of calmodulin-stimulated (Ca(2+)-Mg(2+)-ATPase. Measurements of the steady-state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene indicated that the lipid phase transition of membrane vesicles occurred at 25.9 degrees C and at 28.9 degrees C for preparations isolated from hyperthyroid and euthyroid rabbits, respectively. Arrhenius plot break-point temperature for CaM-stimulated (Ca(2+)-Mg(2+)-ATPase activity was lower in membrane preparations isolated from hyperthyroid (26.9 degrees C) than from euthyroid ones (30.0 degrees C). Thus, the increase of the membrane fluidity presumably caused that the enzyme was characterized by the lower activation energy value. This phenomenon may be viewed as a supplementary mechanism for activation of the enzyme by thyroid hormones to previously reported elevation of the amount of (Ca(2+)-Mg(2+)-ATPase protein exerted by hyperthyroidism (Famulski et al. (1988) Eur. J. Biochem., 171, 363-368; Famulski and Wrzosek (1988) in The Ion Pumps-Structure, Function and Regulation (Stein, W.D., ed.), pp. 355-360, Alan R. Liss, New York).     

In vitro effects of vitamin D3 on the phospholipids of isolated renal brush border membranes

A model system is described in which cholecalciferol (vitamin D3) is incorporated into phosphatidylcholine liposomes and then the liposomes are incubated in vitro with isolated renal brush border membrane vesicles. The incubation results in an alteration of the phospholipid composition, the fluidity, and the transport properties of the membrane. The findings provide evidence consistent with the hypothesis that vitamin D3 and metabolites modify membrane structure and function by "liponomic regulation."