Microdetermination of lipid classes after thin-layer chromatography

Quantitative monitoring of galactolipid hydrolysis by pancreatic lipase-related protein 2 using thin layer chromatography and thymol-sulfuric acid derivatization

Galactolipids are the most abundant lipids on earth where they are mainly found in photosynthetic membranes of plant, algae, and cyanobacteria. Pancreatic lipase-related protein 2 (PLRP2) is an enzyme with galactolipase activity allowing mammals, especially herbivores, to digest this important source of fatty acids. We present a method for the quantitative analysis of galactolipids and galactosylated products resulting from their digestion by guinea pig PLRP2 (GPLRP2), using thin-layer-chromatography (TLC), thymol-sulfuric acid as derivatization reagent and scanning densitometry for detection. Thymol-sulfuric acid reagent has been used for the colorimetric detection of carbohydrates. It is shown here that the derivatization of galactosyl group from galactolipids by this reagent is not affected by the bound acyl glycerol, acyl chains length and number of galactose residues in the polar head. This allowed quantifying simultaneously the initial substrate and all galactosylated products generated upon the hydrolysis of monogalactosyl di-octanoylglycerol (C8-MGDG) by GPLRP2 using a single calibration with C8-MGDG as reference standard. The reaction products, monogalactosyl monooctanoyl glycerol (C8-MGMG) and monogalactosyl glycerol (MGG), were identified and quantified, MGG being recovered from the aqueous phase and analyzed by a separate TLC analysis. This method is therefore suitable to quantify the products resulting from the release of both fatty acids present in MGDG and thereby shows that PLRP2 can contribute to the complete digestion of galactolipids and further intestinal absorption of their fatty acids.

Seasonal dynamic of morpho-physiological properties and the lipid composition of Plantago media (Plantaginaceae) in the Middle Volga region

The changes in morpho-physiological properties and lipid composition have been studied in the leaves of the plant Plantago media collected from two different places in the Middle Volga region during the summer of 2010. The plants gathered from the first plot (P1 plants) grew on plain ground in the midst of typical meadow-steppe perennial plants. The plants of the second group (P2 plants) grew on a flat slope of the South-West exposition, in the grass community. The leaves of the plants Р1 had lower specific area densities but larger areas and masses; they accumulated more levels lipid peroxide products. The changes in lipid compositions depended on the growth phase and habitats. Correlations between morpho-physiological parameters and certain lipids have been established. The amounts of galactolipids (GL) have been shown to correlate with the leaf areas. When the leaf areas were reduced, a ratio between phosphatidylcholines (PC) and phosphatidylethanolamines (PE) decreased. The result of our study showed that gradual changes of morphometrical parameters were accompanied by the alterations in biomass structure and modifications in lipids and fatty acids (FA).

Membrane-forming lipids of wild halophytes growing under the conditions of Prieltonie of South Russia

The composition of membrane-forming lipids has been examined for 10 wild halophyte species growing in southern Russian on alkaline soil. The plants belong to seven taxa of family rank: by their life form, which are semi-shrubs, herbaceous annuals, and perennial plants; their salt tolerance, which are classified as the euhalophytes, crynohalophytes, and glycohalophytes; and by their sensitivity to water, classifications of mesoxerophytes and xeromesophytes. Parallels have been found between the lipid composition and the ecological status of the plants. It has also been revealed that the similarity in the glyco- and phospholipid composition of different plant groups relates to the water factor and the type of salt accumulation, respectively. The fatty acid compositions of the examined plants is determined at the species level.

Cellular responses of microcolonial rock fungi to long-term desiccation and subsequent rehydration

Melanised rock-inhabiting fungi are astonishingly resistant to environmental stresses. Also known as micro-colonial fungi (MCF), they are ubiquitous and even colonise bare rocks in deserts. To survive in nutrient poor and extremely stressful conditions, MCF have reduced morphogenetic complexity to a minimum, and rely on a broad spectrum of stress protection mechanisms. Although visual signs of carotenoid presence are masked by heavily melanised black cell-walls, we were able to isolate and characterise a variety of carotenoids (ss-carotene, zeta-carotene, phytoene, torularhodin and torulene) in the rock-inhabiting, relatively fast-growing strain A95. The desiccation/rehydration stress response was used to measure the ability of A95 to adapt to slow or fast changes in external conditions. Revival of MCF after prolonged desiccation and rehydration was documented by biochemical (analyses of lipids and protective pigments), cultivation, and microscopic methods. Survival of MCF is enhanced when desiccation is rapid and mycostasis is instant rather than following prolonged periods of low metabolic activity.

Hormonal and stressor-associated changes in porcine adrenocortical cholesterol ester hydrolase activity

Cholesterol ester hydrolase (CEH) activity was characterized in the porcine adrenal gland and experiments conducted to determine the nature of its hormonal regulation. CEH activity was studied in the 14,000 gmax pellet (F4) and in the 192,000 gmax supernatant (F6). Characteristics associated with pH optima, product formation with time, linearity with increasing protein concentration, and equilibration of exogenous cholesterol esters added in acetone with endogenous cholesterol esters were determined. Scatchard analyses of saturation data demonstrated two-site models, which indicated the presence of lower velocity lower Km enzymes (catalytic sites) (L-VKm) and higher velocity higher Km enzymes (catalytic sites) (H-VKm) in both subcellular fractions. Neither ACTH (0.4 micrograms/kg body weight) nor 30-min restraint affected CEH activities at 0.5, 2, and 5 h after injection or initiation of restraint. However, 1 h after a longer restraint period (45 min), F4 H-VKm CEH activity increased concomitantly with decreased F6 L-VKm (P = 0.003). More modest increases in F4 H-VKm (P = 0.03) were still apparent 1 h after the last of nine daily 45-min restraints. Bromocriptine (CB154, a dopamine agonist) administration for 6 days (9.6 mg/daily) reduced plasma prolactin (PRL) by 53% (P < 0.05), but had no effect on CEH activities. ACTH treatment to CB154-induced hypoprolactinemic barrows dramatically reduced F4 (63%) and F6 (49%) L-VKm CEH activity (P = 0.03). These data are the first concerned with regulation of adrenal CEH activity in swine, and are the first to evaluate in vivo treatments on in vitro CEH activity in any species evolutionarily higher than rodents. In vivo regulation of porcine adrenal CEH activity appears complex. Stressor-associated hormonal perturbations apparently must surpass a certain threshold of duration and/or magnitude before they alter CEH activity. Differing Km and Vmax of CEH within and between the two subcellular fractions studied and the differential responses to restraint stressor suggest that as many as four different enzymes with CEH activity are involved. Additionally, the combined effect of ACTH and CB154-induced hypoprolactinemia argues for an interrelated modulatory function of ACTH and PRL (or dopamine) on specific porcine adrenal CEH activities.

Analysis of brain and myelin lipids by high-performance thin layer chromatography and densitometry

We have developed a simple method involving high-performance thin layer chromatographic separation of total brain and myelin lipids. Only two solvent systems consisting of chloroform: methanol:acetic acid and water at different concentrations were needed. The plate was then stained with three sequential procedures to visualize phospholipids, cholesterol and galactolipids. Densitometric procedure at each step of staining was utilized to obtain quantitative analysis of brain and myelin samples.

Analysis of lipids by one-dimensional thin-layer chromatography

A high-efficiency silica gel, (type HLF) thin-layer chromatography plate (HETLC), linear high-performance thin-layer chromatography plate (HPTLC) and densitometry method has been devised in order to resolve the major lipid classes obtained from rat brain tissues. This methodology, which has largely overcome prior problems, enhances the opportunity for assessing the glycerophospholipid and glycolipid compositions of tissues. DEAE-Sephadex column chromatography was used to separate the crude lipids extract into neutral and acidic lipid fractions. The lipid fractions were then spotted on separate HPTLC and HETLC plates and chromatographed in one dimension using one solvent system. Quantitation was by in situ densitometry with the absolute quantity of the lipid classes determined from co-chromatographed standards. Sensitivity was increased by using cupric sulfate reagent, which was found to be more sensitive than the conventional cupric acetate reagent. This method is applicable to a broader separation of lipid classes and has improved sensitivity.

Lipid composition of fresh and frozen-stored krill

Lipid classes in seven krill (Euphausia superba D.) samples, fresh and after various periods of storage at 251 K were compared. Fresh krill lipid composition differed from that determined in frozen samples, depending on storage duration, season of harvest, and developmental stage (as determined on a few samples only). Phospholipids proved most susceptible to changes, as opposed to triglycerides, which were most resistant; diglycerides and cholesterol esters were also destroyed. The freezing process per se affected the lipid composition only slightly; however, after 30 days storage the amount of free fatty acids almost doubled. After 6 months storage at 251 K, 70% of phospholipids were decomposed and the amount of free fatty acids increased by a factor of 6 to 20. Monoglycerides, absent from fresh krill, appeared after several months of frozen storage. Juvenile krill were more susceptible to lipolytic changes. Females bearing mature eggs contained stable phospholipids; it was only triglycerides that were hydrolysed. It seems probable that discrepancies encountered in the literature data on krill lipid composition are the result of frozen krill being analysed.

Inhibition of cholesterol synthesis by ketoconazole

To determine if ketoconazole influences cholesterol metabolism in humans, plasma lipid levels were studied in seven men with advanced prostate cancer who were being treated with high-dose ketoconazole. Additionally, the effects of ketoconazole on cholesterol synthesis in cultured normal human fibroblasts were studied. High-dose ketoconazole therapy caused a 27 percent reduction in total serum cholesterol values without affecting serum triglyceride levels. The reduction in serum cholesterol levels was maintained for five months in six of seven patients. The fall in total cholesterol levels was due to a 38 percent reduction in low-density lipoprotein cholesterol levels without associated changes in high-density lipoprotein cholesterol levels. Serum lanosterol levels increased 46 percent during ketoconazole treatment. Studies in cultured normal human fibroblasts showed that ketoconazole inhibited cholesterol synthesis by blocking the conversion of lanosterol to cholesterol. These results establish that ketoconazole is a potent inhibitor of cholesterol production in vivo and in vitro.

Effects of dexamethasone and insulin on the synthesis of triacylglycerols and phosphatidylcholine and the secretion of very-low-density lipoproteins and lysophosphatidylcholine by monolayer cultures of rat hepatocytes

Rat hepatocytes in monolayer culture were preincubated for 19 h with 1 microM-dexamethasone, and the incubation was continued for a further 23 h with [14C]oleate, [3H]glycerol and 1 microM-dexamethasone. Dexamethasone increased the secretion of triacylglycerol into the medium in particles that had the properties of very-low-density lipoproteins. The increased secretion was matched by a decrease in the triacylglycerol and phosphatidylcholine that remained in the hepatocytes. Preincubating the hepatocytes for the total 42 h period with 36 nM-insulin decreased the amount of triacylglycerol in the medium and in the cells after the final incubation for 23 h with radioactive substrates. However, insulin had no significant effect on the triacylglycerol content of the cell and medium when it was present only in the final 23 h incubation. Insulin antagonized the effects of dexamethasone in stimulating the secretion of triacylglycerol from the hepatocytes, especially when it was present throughout the total 42 h period. The labelling of lysophosphatidylcholine in the medium when hepatocytes were incubated with [14C]oleate and [3H]glycerol was greater than that of phosphatidylcholine. The appearance of this lipid in the medium, unlike that of triacylglycerol and phosphatidylcholine, was not stimulated by dexamethasone, or inhibited by colchicine. However, the presence of lysophosphatidylcholine in the medium was decreased when the hepatocytes were incubated with both dexamethasone and insulin. These findings are discussed in relation to the control of the synthesis of glycerolipids and the secretion of very-low-density lipoproteins and lysophosphatidylcholine by the liver, particularly in relation to the interactions of glucocorticoids and insulin.

The effects of monensin on secretion of very-low-density lipoprotein and metabolism of asialofetuin by cultured rat hepatocytes

Primary cultures of rat hepatocytes were used to study secretion of very-low-density lipoproteins and metabolism of asialofetuin. The ionophore monensin inhibited both secretion of very-low-density lipoproteins and binding and degradation of asialofetuin in a concentration-dependent manner. Secretion as well as receptor binding were markedly decreased after 15 min treatment with monensin. The inhibitory effect of the ionophore was fully reversible, and no effect on protein synthesis was observed at concentrations up to 50 microM. The secretion of apoproteins (B-small, B-large and E) and that of albumin were inhibited to the same extent as was triacylglycerol secretion. Secretion of very-low-density lipoproteins was more sensitive to low concentrations of monensin than was the metabolism of asialofetuin. Maximum inhibition of very-low-density-lipoprotein secretion was obtained at 5-10 microM-monensin, whereas 25 microM was required to obtain maximum inhibition of binding and degradation of asialofetuin. The number of surface receptors for asialofetuin decreased to about half when the cells were exposed to 25 microM-monensin. It is possible that monensin inhibits endo- and exo-cytosis via a similar mechanism, e.g. by disturbing proton gradients. Since secretion of very-low-density lipoproteins was more sensitive to low concentrations of monensin, it is likely that monensin independently inhibits endocytic and secretory functions in cultured hepatocytes.

Mobilization of stored triglycerides from macrophages as free fatty acids

Because many or most lipid-laden foam cells in atheromas and in xanthomas derive from macrophages, it is important to understand how they accumulate lipids and how they can divest themselves of lipids. The mobilization of stored triglycerides from macrophages was studied in cell cultures. Mouse resident peritoneal macrophages and J774 macrophages increased their triglyceride content six- to tenfold during a 24-hour incubation with free fatty acids complexed to albumin. Subsequent incubation in fresh medium containing free fatty acid-poor albumin was accompanied by a fall in cell triglyceride content (50% in 20 hours) and a corresponding increase in medium-free fatty acid. Release of free fatty acid was linear as a function of time, provided fresh medium was added hourly. When medium was not changed, release rates fell off rapidly, probably due to re-uptake of released free fatty acid. Chloroquine did not affect the rate of free fatty acid release. The results suggest that macrophages-foam cells can reduce their triglyceride stores via the action of a nonlysosomal (presumably cytoplasmic) neutral triglyceride lipase.

Lipoprotein synthesis and secretion by cultured rat hepatocytes. Parallel inhibition of secretion of VLDL, HDL and albumin by monensin

The biosynthesis and secretion of very-low-density lipoproteins (VLDL) and high-density lipoproteins (HDL) by cultured normal rat hepatocytes was investigated with particular emphasis on its modification by monensin. This acidic ionophore coordinately inhibited the rates of secretion of the several VLDL apolipoproteins and the VLDL lipids, suggesting an effect late in the process of biosynthesis and secretion, probably at the stage of exiting from the Golgi apparatus. The secretion of immunoreactive albumin into the medium was comparably inhibited, implying that the pathway and mechanisms involved in albumin secretion may be closely similar to those for VLDL synthesis and secretion. Secretion of phospholipids and of apolipoproteins E and A-I in the HDL fraction increased progressively with time over 18 h in control incubations but was strongly inhibited by monensin. During extended incubation with monensin at high concentrations (10 microM), there was a net release to the medium of a number of hepatocyte proteins, including some that comigrated with apolipoprotein A-I and apolipoprotein C, making it appear that monensin increased the secretion of these apolipoproteins. However, using labeled amino acids, it was shown by autoradiography and by immunoprecipitation that secretion of newly-synthesized, radioactive apolipoprotein A-I and apolipoprotein C was actually inhibited by monensin. These results are compatible with the conclusion that HDL synthesis and secretion may occur by mechanisms closely related to those for synthesis and secretion of albumin and VLDL.

Inhibition by chloroquine of the secretion of very low density lipoproteins by cultured rat hepatocytes

Cultured rat hepatocytes were incubated in medium containing 1.0 mM oleic acid. The incorporation of [3H]glycerol into cell-associated and medium triacylglycerols was measured after 2 h incubation. More than 95% of the secreted [3H]triacylglycerols were recovered in the very low density lipoprotein (VLDL) fraction (d less than 1.006). Chloroquine and other lysosomotropic amines promoted a marked decrease in [3H]triacylglycerol secretion from the hepatocytes while the synthesis was unaffected. At 50-200 microM final concentration, chloroquine inhibited secretion of triacylglycerols by 70-90% of the control. Similar results were obtained when the mass of secreted triacylglycerols was measured. Chloroquine caused decreased secretion of [3H]triacylglycerols after 15-30 min incubation and the inhibitory effect was completely reversible within 1-2 h after washout of chloroquine. The reduced triacylglycerol secretion was not due to increased reuptake of secreted lipoproteins or decreased protein synthesis caused by chloroquine. Electron microscopy of chloroquine-treated cells showed that the inhibition of VLDL secretion occurs at or prior to the level of the Golgi apparatus. These results suggest that chloroquine interferes with crucial steps in the secretory process and/or that lysosomal function could be essential for secretion of VLDL.

Uptake and degradation of human chylomicrons by macrophages in culture. Role of lipoprotein lipase

Because macrophages secrete lipoprotein lipase (LPL), we sought to determine if LPL activity would influence the metabolism of chylomicrons by macrophages. In initial studies, we showed that normal chylomicrons were a substrate for the macrophage's LPL activity. Uptake of normal chylomicrons occurred in a saturable fashion and was effectively competed for by human chylomicrons, very low density lipoproteins (VLDL), and rabbit beta-VLDL, but not by acetyl-low density lipoprotein (LDL), and only modestly by native LDL. When apoprotein C-II-deficient chylomicrons were incubated with macrophages, no hydrolysis of triglyceride occurred, yet saturable uptake of chylomicron protein and lipid occurred, demonstrating that LPL activity is not a prerequisite for saturable uptake. However, addition of apo C-II led to marked hydrolysis and enhanced uptake of protein and lipid moieties. When albumin was present in the medium, there was approximately equal enhancement of cellular content of triglyceride and cholesteryl ester, despite the fact that chylomicrons are triglyceride-rich. This was due to uptake of a triglyceride-depleted particle produced by LPL, as well as a preferential re-release of triglyceride. These studies suggest potential pathways by which triglyceride-rich lipoproteins could contribute to accumulation of cholesteryl esters in macrophages, even while only small amounts of triglyceride accumulate.

Effects of insulin and glucose on very low density lipoprotein triglyceride secretion by cultured rat hepatocytes

The effect of insulin on hepatic triglyceride synthesis and secretion is controversial. Previously, we have described a cell culture system of adult rat hepatocytes that synthesize and secrete very low density lipoprotein (VLDL) triglycerides with small and irreproducible effects of insulin on triglyceride metabolism. To study the primary effects of insulin on hepatic triglyceride metabolism a method was developed utilizing fibronectin-coated culture dishes that allowed adhesion, spreading, and maintenance of hepatocytes for 2-3 d in the absence of serum and insulin. This culture system allowed mass measurements of both cellular and secreted VLDL triglycerides for long time periods after the addition of physiological concentrations of insulin to hormone-free culture medium. In the absence of insulin and after an initial 4 h in culture, the medium was replenished and triglyceride mass was measured at the end of 18-h incubations. VLDL triglyceride accumulated in the culture medium at a linear rate over this time-course with increasing accumulation as the medium glucose concentration was raised from 2.5 to 25 mM glucose (1.77+/-0.24 to 3.09+/-0.76 mug triglyceride/mg cell protein per h). There was no apparent significant lipolysis or hepatocellular reuptake of secreted VLDL triglycerides. In the absence of insulin cellular triglyceride levels were unchanged between 3 and 24 h in culture while insulin (50-500 muU/ml) significantly increased cellular triglyceride content at all glucose concentrations tested (0-25 mM). The addition of insulin to the culture medium progressively reduced the rate of VLDL triglyceride secretion accompanied by an increase in cellular triglyceride at insulin concentrations > 50 muU/ml. Most or all of the observed increase in cell triglyceride content could in all experiments be accounted for by the insulin-induced inhibition of VLDL secretion. Incorporation of [2-(3)H]glycerol into cellular and VLDL triglycerides as a function of insulin concentration was also measured. Glycerol incorporation data at 20-22 h after plating of the cells closely paralleled the insulin-induced changes in cellular and VLDL triglyceride as determined by mass analysis. The observed effects of insulin occurred at concentrations close to the physiological range and suggest that the direct hepatic effect is to suppress VLDL secretion although the net effect in vivo will clearly reflect many additional accompanying changes.

Effects of adrenocorticotropin and cycloheximide on adrenal diglyceride kinase

We studied the effects of adrenocorticotropin (ACTH) and cycloheximide on adrenal enzymes involved in phosphatidate synthesis. Treatment of rats in vivo with ACTH induced a rapid increase in phosphatide synthesis from diglyceride and ATP in adrenal homogenates, and cycloheximide treatment prevented this increase if given before ACTH and rapidly reversed the increase if given after ACTH. The stimulatory effect of ACTH appeared to be largely due to an increase in diglyceride substrate, as kinase activity was not altered. The inhibitory effect of cycloheximide, on the other hand, appeared to be due to a decrease in diglyceride kinase activity. Neither ACTH nor cycloheximide treatment had any effect on the activity of glycerol-3'-phosphate acyltransferase or phosphatidate phosphatase. Our findings suggest that (a) ACTH increases the flow of phospholipid (and their levels) throughout the entire circular pathway, i.e., phosphatidate leads to CDP-diacylglycerol leads to inositides leads to diglycerides leads to phosphatidate, and (b) a labile protein may serve to allow entry into a recycling of diglyceride in this pathway. In addition, since cycloheximide blocked carbachol-induced increases in pancreatic and salivary glandular phosphatidate synthesis resulting from phosphatidylinositol hydrolysis and consequent diglyceride generation, the putative labile protein may have widespread importance.

Changes in lipid levels of three skeletal muscles following denervation

Nonpolar and polar lipids extracted from denervated rat gastrocnemius, plantaris, and soleus muscles were measured 7-9 days after unilateral sciatic nerve transection. The contralateral muscle (CCON) was used to obtain control lipid levels. After denervation changes in lipid concentrations were found in all three muscles. These alterations in lipid levels were generally in same direction but not to the same extent. The change in total nonpolar lipids (NL) was an increase in soleus greater than gastrocnemius greater than plantaris concentration. This change in lipid concentration was more apparent than real since the wet weight of muscle was decreased after denervation. Since polar lipid (PL) concentrations were not increased under these conditions of muscle weight loss, an actual decrease of polar lipids after denervation may be inferred. In contrast to the other two muscles, a marked difference was noted for polar lipids of denervated gastrocnemius muscle. An unidentified spot near the origin was detected. This area is the location of a nerve sprouting factor(s). The compound(s) was not detectable for the other two muscles. When the gastrocnemius from an unoperated animal rather than a CCON muscle was used as a benchmark, slight increases were found for total nonpolar, polar, and plasmalogen fractions following denervation. The changes for individual lipid fractions were less definable, except for the significant increase for the unknown polar compound near the origin. This spot was noted in extracts from CCON and DEN muscles but not in untouched control muscle. The CCON gastrocnemius muscle is therefore a poor control for determining effects of denervation on lipid levels and perhaps other biochemical parameters as well.

New function for high density lipoproteins. Isolation and characterization of a bacterial lipopolysaccharide-high density lipoprotein complex formed in rabbit plasma

The addition of bacterial lipopolysaccharide (LPS) from Salmonella minnesota R595 to rabbit plasma results in a marked reduction of the hydrated buoyant density of the parent R595 LPS, from 1.38 to less than 1.2 g/cm3. Using immunopurified anti-R595 LPS antibody covalently linked to Sepharose 4B, we were able to separate the altered R595 LPS (d less than 1.2 g/cm3) from the remainder of the plasma proteins by elution of the bound material with 2.5 M KSCN. The KSCN eluate was shown to have a d less than 1.2 g/cm3 and to contain both R595 LPS as well as protein and lipid characteristic of high density lipoprotein (HDL). The major protein in the KSCN eluate is a single polypeptide chain with an apparent molecular weight of 26,000 in sodium dodecyl sulfate and an amino acid composition essentially identical to that of apoprotein AI, the major protein of rabbit HDL. The lipid composition of the KSCN eluate is similar to that of HDL, although marked differences in the cholesterol ester/cholesterol ration and the phosphatidyl choline/phosphatidyl ethanolamine ratio were observed when the KSCN eluate and rabbit HDL were compared. The formation of this R595 LPS-protein-lipid complex in plasma accounts for the marked reduction in buoyant density found when LPS is added to plasma.

Polyenoic acid metabolism in cultured human skin fibroblasts

The incorporation of [1-14C]linoleic acid, and [1-14C]linolenic acid into cellular lipids of cultured human skin fibroblasts was studied. Cultured cells took up both labeled fatty acids at nearly the same rate and incorporated them into a variety of lipid classes. At the end of 1 hr incubation with [1-14C]linoleic acid, radioactivity was found in the triacylglycerol (TG) and choline phosphoglyceride (CPG) pools preferentially. Incorporation into the TG fraction decreased rapidly, while the uptake into CPG, serine phosphoglyceride (SPG), and ethanolamine phosphoglyceride (EPG) fractions increased progressively with longer incubation times. Similar results were obtained with [1-14C]linolenic acid as precursor. At the end of 24 hr, desaturation and chain elongation of 18:3 n-3 was more extensive than conversion of 18:2 n-6 to higher polyenoic acids. During pulse-chase experiments with either fatty acid precursor, the incorporated radioactivity was progressively lost from cellular lipids, particularly from the TG and CPG fractions, but continued to increase in the SPG and EPG pools. The similar labeling pattern of cellular phospholipids with linoleic or linolenic acids, and data from pulse-chase studies suggest that a direct transfer of fatty acids from CPG to EPG is a likely pathway in fibroblast cultures. Incorporation into the EPG pool during the pulse-chase experiments paralleled extensive desaturation and elongation of linoleic acid to 20:4 n-6, and 22:4 n-6; and of linolenic acid into 22.5 n-3 and 22:6 n-3.

Spark Discharge: Application Multielement Spectrochemical Analysis

Spark discharge is shown to be a cyclic process of energy dissipation, with one spark in a time-connected train influenced by its relation to predecessor sparks. Spectroscopic instruments having temporal, spatial, and spectral resolution indicate that the light emission is highly ordered with cylindrical symmetry about the current-conducting spark channel. The favored spatial coincidence is between the channel and the most highly ionized and most excited species sampled from the cathode, with less ionized and less excited species emitting farther outward. Light absorption occurs to such an extent that there are full line reversals in excited states of magnesium ions, distant from the channel. Schlieren data indicate a toroidal structure in the postdischarge environment. Charge transfer, Penning ionization, and sensitized fluorescence are thought to be the chemical mechanisms responsible for the spectroscopic topography. Experiments in spectrochemical analysis based on the topography and designed for increased sensitivity, reduced matrix effects, and simpler spectra are discussed.