The functioning of the lipids and lipoproteins of sarcotubular membranes in calcium transport

In the intact muscle cell, an internal tubular membrane system called the sarcoplasmic reticulum (SR) plays an important role in the contraction-relaxation cycle by controlling the Ca⁺⁺ of the myoplasm; release of Ca⁺⁺ from the SR to myoplasm initiates contractile activity and sequestring Ca⁺⁺ in the SR by means of a transport system causes muscle to relax. Fragments of the SR with a vesicular structure can be isolated from muscle homogenate and these vesicles are able to vigorously transport Ca⁺⁺ from incubation media into the intravesicular space thus enabling study of Ca⁺⁺ transport under precisely defined in vitro conditions. A highly purified fraction of SR vesicles called SF₁ were prepared from rat muscle by means of density gradient centrifugation procedures. The role of SR lipid in Ca⁺⁺ transport was studied. SF₁ was treated in vitro with either phospholipase A or C or D or polyene antibiotics. The effect of essential fatty acid deficiency, induced in vivo, was also investigated. It was concluded that the only structural feature of SF₁-lipid involved in Ca⁺⁺ transport and the associated adenosine triphosphatase is the phosphoryl moiety of the phospholipids. Evidence was obtained which inplicated histidine residues of the SF₁ protein in this transport function. To study the role of SF₁ protein in this process in depth, the membranes were solubilized by a sodium dodecylsulfate system and made free of their lipid components. More than 95% of this protein is soluble in dilute salt solution; of this, more than 90% is composed of a protein fraction which can be isolated by gel filtration (called protein fraction-2). Protein fraction-2 contains large molecular aggregates of small polypeptide subunits of identical or nearly identical molecular weight. They contain solely N-terminal glycine and probably only C-terminal alanine. The significance of such a high percentage of similar polypeptide subunits in SR is discussed. One of five papers to be published from the Symposium “Lipid Transport” presented at the AOCS Meeting, New Orleans, April 1970.     

Effect of dietary fat on the fluidity of platelet membranes

Dietary fat type was reflected in the phospholipid fatty acid composition of the plasma membrane of rabbit platelets and apparently controlled the fluidity of these membranes. Rabbits were maintained for 6 months on diets that varied in stearic and polyunsaturated fatty acids and thus had different potentials for thrombosis. Microviscosities at 37 C, calculated from the anisotropy of fluorescence from the probe 1,6-diphenyl-1,3,5-hexatriene, were 3.5, 3.4, 2.8 and 2.2. poise for platelet membranes isolated from rabbits whose only source of dietary fat was cocoa butter, milkfat, coconut oil, or corn oil, respectively. The relative fluidities of the membrane isolates were correlated with the polyunsaturated fatty acid contents of the membrane phospholipids.     

Effect of dietary polyunsaturated pork on plasma lipids and sterol excretion in man

Pork, enriched in linoleic acid content, was compared with conventional pork in the diet of three human subjects with respect to the plasma cholesterol concentration and the excretion in feces of neutral sterols and bile acids. Since the fatty acids in pork glyceride have an unusual positional distribution, the redistribution that might occur during the absorption and disposition of a fat meal was also studied. The plasma cholesterol was lower with polyunsaturated pork, the difference, 14 mg/100 ml plasma, being of the order expected from the change in polyunsaturated to saturated fatty acid ratio. On average, the excretion of neutral sterols was 57% greater with polyunsaturated than with conventional pork in all three subjects, and in this respect the results resembled the findings with polyunsaturated ruminant fats. During the absorption of pork fat, the high proportion of palmitate in the 2 position of lard triglyceride served as a useful marker, since human triglyceride carries mainly unsaturated fatty acids in that position. There were stepwise changes in the fatty acid composition at the 2 position of triglyceride as the fat was absorbed, transported through, and cleared from plasma, the palmitate being gradually replaced by oleate and linoleate. By contrast, the total fatty acid profile in the triglyceride changed relatively little, implying selective reacylation with palmitate at the 1 and/or 3 position. During the clearing of dietary triglyceride, the porcine triglyceride was thus converted to the form occurring in humans.     

Effect of dietary palm oil and its fractions on rat plasma and high density lipoprotein lipids

Male Sprague Dawley rats were fed semipurified diets containing 20% fat for 15 weeks. The dietary fats were corn oil, soybean oil, palm oil, palm olein and palm stearin. No differences in the body and organ weights of rats fed the various diets were evident. Plasma cholesterol levels of rats fed soybean oil were significantly lower than those of rats fed corn oil, palm oil, palm olein or palm stearin. Significant differences between the plasma cholesterol content of rats fed corn oil and rats fed the three palm oils were not evident. HDL cholesterol was raised in rats fed the three palm oil diets compared to the rats fed either corn oil or soybean oil. The cholesterol-phospholipid molar ratio of rat platelets was not influenced by the dietary fat type. The formation of 6-keto-PGF_1α was significantly enhanced in palm oil-fed rats compared to all other dietary treatments. Fatty acid compositional changes in the plasma cholesterol esters and plasma triglycerides were diet regulated with significant differences between rats fed the polyunsaturated corn and soybean oil compared to the three palm oils.     

Effect of dietary lipids on the lipid composition and phospholipid deacylating enzyme activities of rat heart

Rats were fed lard-enriched (17%) or corn oil-enriched (17%) diets and were compared with rats fed a low fat (4.5%) diet. Cardiac protein, DNA, phospholipid (PL) and fatty acid (FA) compositions were analyzed. Neutral phospholipase A, lysophospholipase and creatine kinase activities in the membrane and cytosolic compartments were also investigated. No significant modification of cardiac protein, DNA nor PL was observed among the three groups. Some alterations appeared in the FA composition. A lard-enriched diet induced a significant increase of 22∶5n−3 and 22∶6n−3 in heart phosphatidylcholine (PC) and phosphatidylethanolamine (PE), whereas a linoleic acid-rich diet induced a specific increase of 22∶4n−6 and 22∶5n−6 in these two major PL. Compared to rats fed the low fat diet, membrane-associated phospholipase A activity, measured by endogenous hydrolysis of membrane PC and PE, showed a significant increase (+45%) for both PL in rats fed corn oil. However, the activity of membrane-associated phospholipases, measured with exogenous [1-¹⁴C]dioleoyl PC, was not different among the three groups of rats. Cytoplasmic activity was decreased in rats fed corn oil, and lysophospholipase and creatine phosphate kinase activities were not significantly affected by diet. FA modification of the long chain n−6 FA induced by corn oil may be responsible for the observed increase in phospholipase activity. Physiological implications are suggested in terms of membrane degradation and prostaglandin production. Presented in part at the International Symposium on Lipid Metabolism in the Normoxic and Ischemic Heart, Rotterdam, The Netherlands, September 1986.     

Effect of early postnatal dietary sterculate on the fatty acid composition of rat liver and brain lipids

Pregnant rats were fed a high carbohydrate diet containing either 1% trilinolein or 1% trilinolein with 0.2% methyl sterculate from 18 day gestation to 21 day postpartum. The pups were weaned at 21 days and continued on the same diet for an additional 10 days. The microsomal stearyl CoA desaturase activities of the liver were effectively inhibited. Liver triglycerides showed increases in the saturated fatty acids concentrations at the expense of the corresponding monoenes. The concentration ofcis 6–7 octadecenoic acid was elevated. In liver phospholipids, the concentration of stearic acid was increased without a corresponding decrease in the oleic acid content. A drastic decrease in the nervonic acid (24∶1, n−9) concentration of liver sphingomyelin was observed. The lipids of the brain did not contain sterculic acid, and brain desaturase activity was unaffected. There was no significant change in the concentration of monoenoic acids from 16∶1 to 22∶1. However, nervonic acid was decreased by 32%. These results suggest that brain nervonic acid may be derived from a precursor other than oleic acid.     

Effect of dietary α-linolenic acid on n−3 fatty acids of rainbow trout lipids

The effects of α-linolenic acid enriched diets on the lipid composition of rainbow trout (Oncorhynchus mykiss) muscle and liver were determined. Diets containing 0, 4, 10 or 20% (wt/wt) linseed oil were fed to 280 trout for up to 64 days. Linolenic acid levels in total lipid, neutral lipid and phospholipid of liver and muscle increased with duration of intake. The linolenic acid content of total lipid in muscle increased from 10 mg to 355 mg/100 g flesh. There was no significant increase in the elongated desaturated products, i.e., eicosapentaenoic or docosahexaenoic acids, in either tissue during the feeding period.     

Interaction between dietary proteins and lipids in the regulation of serum and liver lipids in the rabbit. Effect of fish protein

Purified diets varying in dietary protein, namely casein (CA), soy protein (SP), fish protein (FP), and lipid origin (corn oil (CN), coconut oil (CO)) were fed to rabbits to evaluate the effects of protein and fat source, as well as protein-lipid interactions, on serum total, lipoprotein and hepatic lipid levels. Dietary proteins and lipids exerted a separate effect on serum total cholesterol (C), very low-density lipoprotein cholesterol (VLDL-C), and low-density lipoprotein cholesterol to high density lipoprotein cholesterol (LDL-C/HDL-C) ratio. Hence, CA increased serum cholesterol compared to SP, while coconut oil enhanced serum and VLDL-C, and decreased LDL-C/HDL-C compared to corn oil. Dietary proteins interacted with dietary lipids to modulate HDL-C levels. Thus, FP maintained a high level of HDL-C regardless of lipid origin, compared to CA and SP whose HDL-C levels were decreased by corn oil, compared to coconut oil. A dietary protein-lipid interaction was also observed in the regulation of liver cholesterol levels. Coconut oil, compared to corn oil, decreased liver cholesterol in rabbits fed FP, whereas hepatic cholesterol concentration was unaltered by dietary lipid source in CA- and SP-fed rabbits. These results demonstrate that dietary proteins act synergistically with dietary lipids to regulate cholesterol metabolism in the rabbit. This work was presented in part at the 74th Annual FASEB meeting held in Washington, D.C., April 1–5, 1990.     

Influence of dietary fiber on lipids and aortic composition of vervet monkeys

A semipurified, cholesterol-free diet containing 40% carbohydrate can produce aortic sudanophilia or aortic atherosclerosis in vervet monkeys (Ceroopithecus aethiops pygerethrus) depending on the particular carbohydrate fed. Four groups of vervet monkeys (three males and three females per group) were fed semipurified diets containing lactose. Two of the groups were also fed 15% cellulose (C) or 15% cellulose plus 0.1% cholesterol (CC); the two other groups were fed 15% pectin (P) or 15% pectin plus 0.1% cholesterol (PC). The average serum total cholesterol and low density lipoprotein cholesterol levels over the entire feeding period (mg/dl±SEM) were, for C, 156±14 and 95±5; for P, 173±15 and 112±8; for CC, 187±27 and 122±21; and for PC, 155±11 and 108±7. Cholesterol levels at autopsy (mg/dl±SEM) were, for C, 103±6; for P, 108±16; for CC, 92±9; and for PC, 106±7. Aortic sudanophilia (percentage of area) was, for C, 5.9±2.7; for P, 13.5±9.4; for CC, 5.3±2.1; and for PC, 21.6±10.3. Dietary pectin led to more severe sudanophilia (increased by 129% in the absence of cholesterol and by 308% in its presence) than did cellulose. Analysis of aortic glycosaminoglycans (GAG) revealed that dermatan sulfate levels fell in both cholesterol-fed groups, and chondroitin sulfate fell in aortas of group CC. Heparan sulfate levels were unaffected by cholesterol feeding. Hexuronic acid, galactosamine and hexosamine levels were elevated in the pectin-fed monkeys, but levels were unaffected by dietary cholesterol. Pectin may contribute galactosamine and glucuronic acid towards aortic GAG.     

Effect of dietary components on the pathobiology of colonic epithelium: Possible relationship with colon tumorigenesis

The concept that diet plays an important role in the initiation and/or development of various types of tumors in man and experimental animals is well documented. The etiology of colon cancer is complex and multifactorial in nature, and these is little information on the dietary components that may act as initiators during colon tumorigenesis. We have evaluated various dietary heterocyclic mutagenic amines present in a typical “Western” diet for their nuclear damaging effect (presumably a genotoxic response) on the colonic epithelium of C57BL/6J mice in vivo. Among the mutagenic amines studied, 2-amino-3,4-dimethylimidazo(4,5-f)quinoline and 2-amino-3-methylimidazo(4,5-f)quinoline were very potent inducers of nuclear aberrations. These observations provide us with clues that our daily diet may contain colon-specific genotoxic components. Promotional effects of dietary fat and/or bile acids on colon tumorigenesis have been well studied. Dietary levels of calcium (0.1, 0.5 or 1.0% by weight) appear to modify the toxicity of orally administered fat or cholic acid (assessed by quantifying cell proliferation). The colons of animals consuming 0.1% or 0.5% calcium diet were more susceptible to the toxicity, whereas the colons of those consuming a 1.0% calcium diet appeared more like control colons. These studies demonstrate a profound effect of dietary constituents on the pathobiology of the colonic epithelium which may have a marked influence on the colon tumorigenesis.     

Precipitation of calcium carbonate on reverse osmosis membranes

The precipitation of calcium carbonate from aqueous solutions was investigated in a laboratory reverse osmosis cell. Solutions of sodium chloride and calcium bicarbonate, resembling hard brackish water, were desalted in the batch test cell using cellulose acetate membranes at a pressure of 40 bar. Desalting of hard water resulted in a significant reduction of the water flux due to the precipitation of calcium carbonate on the membrane. Precipitation is caused by the high permeability of carbon dioxide through the membrane, resulting in a higher pH of the brine. The experimental results are related to the chemical equilibrium of calcium bicarbonate, the mass transfer of the various species through the membrane, and the crystallization kinetics of calcium carbonate.     

Effect of dietary lipids on fatty acid composition of body lipid in rainbow trout (Salmo gairdneri)

Three isocaloric diets were prepared. Diet 1 (Control) contained 22% herring oil. In diets 2 and 3, a third and a half of the herring oil was replaced, respectively, by an animal fat (lard) which contained a high percentage of saturated fatty acids. Each diet was fed to duplicate groups of rainbow trout for 14 wk. The results of the feeding trial indicated that the concentration of the saturated fatty acids in trout body lipid did not increase despite the high concentration of these fatty acids in Diets 2 and 3. Fish growth, feed efficiency, mortality and the level of fatty acid deposited in fish body lipid and phospholipids are discussed. Technical Paper No. 4440, Oregon Agricultural Experiment Station, Oregon State University, Corvallis, OR 97331.     

Effect of dietary calcium during pregnancy and lactation on zinc levels in blood and bone, in rats

The effect of dietary calcium (Ca) level on maternal zinc (Zn) nutritional status was studied. Female Wistar rats, weighing 250-350 g, were fed during pregnancy and lactation with an experimental diet containing/100 g different levels of calcium: 0.2 g (low calcium: LCa), 0.6 g (normal calcium: NCa) or 0.9 (high calcium: HCa). Maternal blood samples were drawn from the tail at delivery and at the end of lactation. Laboratory determinations were: Zn in whole blood (WB) at delivery and weaning; Zn (ZnF) and Ca (CaF) in the ashed femur at weaning. The results (mean +/- SEM) were: ZnWB (microgram/ml) at delivery and weaning: LCa: 8.73 +/- 1.05; 12.8 +/- 2.02; NCa: 3.49 +/- 0.19; 3.73 +/- 0.37; HCa: 3.21 +/- 0.19; 3.85 +/- 0.27. CaF (mg/100 mg): LCa: 19.2 +/- 0.8; NCa: 21.4 +/- 0.6; HCa: 20.4 +/- 1.1. ZnF (microgram/100 mg): LCa: 30.2 +/- 0.9; NCa: 24.1 +/- 0.3; HCa: 24.1 +/- 0.9. ZnWB was significantly higher in LCa (p < 0.0001) regarding NCa and Hca. ZnF showed an increase and CaF a decrease in LCa regarding NCa and HCa (p < 0.0001). There were no significant differences in ZnWB, ZnF and CaF between NCa and HCa These results show that: there was no detrimental effect when dietary Ca content was increased by 50% above the normal requirements of the rat.; low dietary Ca during pregnancy and lactation produced an increase of Zn utilization, reflected in maternal blood Zn and in ZnF content.     

On the orientation of lipids in chloroplast and cell membranes

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

Origin of the high saturated fatty acid content of rat fecal lipids

The biohydrogenation of unsaturated fatty acids and the preferential absorption of unsaturated fatty acids over long chain saturated fatty acids from the gut have been investigated to find the origin of the high saturated fatty acid content of the facal lipids of rats fed soybean oil. Label from dietary (1-¹⁴C)-linoleic acid was recovered in the saturated and monounsaturated fatty acids of the fecal lipid. However, when (9,10-³H)-stearic acid and (1-¹⁴C)-linoleic acid were fed together, the isotope ratio (³H/¹⁴C) of the fecal lipid was 1.9 times that of the diet. It is concluded that both processes occur.     

A comparison of lipids from liver and hepatoma subcellular membranes

Subcellular fractions of nuclei, mitochondria, endoplasmic reticulum, plasma membrane and cytosol were prepared from liver and hepatoma 72288CTC. Marker enzyme activities, biochemical compositions and electron microscopy were used to establish purity. Hepatoma NADH: cytochrome C reductase and 5′-nucleotidase exhibited abnormal subcellular distributions. The lipids from the subcellular fractions were examined in detail. Mitochondria and plasma membranes were characterized by elevated percentages of diphosphatidylglycrerol and sphingomyelin, respectively, in both tissues. All hepatoma subcellular fractions contained dramatically elevated levels of sphingomyelin and cholesterol, two components that form preferential strong complexes in vitro. The fatty acid composition of hepatoma sphingomyelin differed markedlg from liver and, unlike liver, did not exhibit organelle specific compositions. Some hepatoma lipid classes contained reduced percentages of palmitate while others contained higher levels. Hepatoma phosphatidylcholine and phosphatidylethanolamine from organelles contained lower percentages of long chain polyunsaturated fatty acids than liver. Generally, unique fatty acid profiles exhibited by individual phospholipid classes of liver subcellular fractions were absent or much reduced in the hepatoma. The ratios of oleate to vaccenate were near one for most of the phospholipid classes of most liver fractions, but all hepatoma classes, with few exceptions, contained a much higher percentage of oleate in all subcellular fractions. The hypothesis is proposed that the origin of some acyl moieties for the biosynthesis of various hepatome lipid classes differs from liver sources. The possible changes in acyl pools, sources and compartments for complex lipid biosynthesis could result in change in the quantities of molecular species that could contribute to the abnormal properties of the hepatoma membranes.     

Effect of fructose on rat lipids

Young and mature albino rats were fed Purina chow with and without fructose in the drinking water, and the lipid contents in the serum and livers were determined. Fructose elevated the serum triglyceride and caused an accumulation after 24 hr of liver triglyceride in fed but not fasted mature rats. In young male rats, the liver triglyceride was increased initially but was not found after 10 days. Serum phospholipids were increased in young and mature rats; the content and specific activity of the high density (HD)-lipoproteins being increased in young rats. In vivo incorporation of labeled acetate into liver cholesterol was reduced. Results suggest that fructose or triglyceride metabolism, or both, in rats differ with age.     

Effect of androgens on serum lipids and lipoproteins

The effects of androgens on lipid transport and metabolism have been reviewed. These effects are probably independent of the androgenic and anabolic activities of the androgens, although the molecular mechanism of action is still not known. Presumably the lowering by androgens of the concentrations of serum lipids and lipoproteins could be the consequence possibly of a primary, inhibitory effect on the synthesis of apolipoprotein A. In addition the role of increased lipolytic activities in plasma and of effects on intermediatry metabolism has been considered. Special Fellowship Awardee (1F11 NSO2245-01) from the National Institute of Neurological Diseases and Stroke One of eight papers presented at the symposium “Recent Advances in Drugs Affecting Lipid Metabolism,” AOCS Meeting, Houston, May 1971.