Neutral lipids and phospholipids from cultured astroblasts

Incorporation into phospholipid classes and metabolism via desaturation and elongation of various 14C-labelled (n-3) and (n-6) polyunsaturated fatty acids in trout astrocytes in primary culture

The incorporation and metabolism of [1-14C]18:3(n-3), [1-14C]20:5(n-3), [1-14C]18:2(n-6), and [1-14C]20:4(n-6) were studied in primary cultures of trout brain astrocytes. There were no significant differences between the amounts of individual fatty acids incorporated into total lipid at 22 degrees C, with greater than 90% of all the fatty acids being incorporated into polar lipid classes. The distributions of 18:2(n-6), 18:3(n-3), and 20:5(n-3) in individual phospholipid classes at 22 degrees C were very similar, with 57-63 and 18-24% being incorporated into phosphatidylcholine and phosphatidylethanolamine, respectively. Approximately equal amounts of 20:4(n-6), approximately 30% of the total, were incorporated into each of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol. The metabolism of the (n-3) fatty acids to longer-chain and more unsaturated species was significantly greater than that of (n-6) acids, but delta 4-desaturase activity was very low. A culture temperature of 10 degrees C increased the incorporation of all the fatty acids into total lipid and that of C20 fatty acids into polar lipid. At 10 degrees C, the incorporation of C20 fatty acids into phosphatidylethanolamine and phosphatidylinositol was increased, and the incorporation into phosphatidylcholine and phosphatidylserine was decreased. The distribution of C18 fatty acids was unchanged at the lower temperature, as was the desaturation and elongation of all the polyunsaturated fatty acids incorporated.

Plasma membrane lipids of bovine adrenal chromaffin cells

The lipid composition of plasma membranes isolated from bovine adrenal chromaffin cells has been determined. Choline and ethanolamine phosphatides were predominant; the level of lyso compounds was very low. The amount of cholesterol and the cholesterol/phospholipid molar ratio was low compared to those of the other subcellular fractions of chromaffin cells. A complex pattern of neutral glycolipids was observed in contrast to that of gangliosides.

Brain myelin of genetically obese mice

Brain myelin was studied in genetically obese (ob/ob) mice and compared with that of normal (+/+) mice from the same strain. The brain from obese mice had a significantly lower amount of myelin, and marked changes in the fatty acid composition of myelin were observed. In contrast, the myelin cholesterol: phospholipid: galactolipid and the cerebroside: sulfatide molar ratios and also the phospholipid composition were normal. 2',3'-Cyclic nucleotide 3'-phosphohydrolase (CNP) and UDP-galactose ceramide galactosyltransferase (CGalT) enzymatic activities were normal, and 3'-phosphoadenosine 5'-phosphosulfate (PAPS): cerebroside sulfotransferase (CST) was only slightly decreased. Cholesterol esters were not present in the mutant. These results indicate that brain myelination is affected in obese mutant mice.

Phospholipid-induced changes of gamma-aminobutyric acid transport in cortex grey matter in culture

The function of membrane phospholipids (PL) in the regulation of gamma-aminobutyric acid (GABA) transport and GABA carrier binding has been investigated in organized cultures of rat cerebral cortex. The cellular lipid composition has been changed by growing the cells in a delipidated nutrient solution or by short-term exposure of the cells to PL emulsions. Introduction of PL into the cellular matrix was monitored by analysis of biologically active fluorescently labeled phosphatidylcholine (PC) or phosphatidylethanolamine (PE). Parinaroyl and dansyl derivatives were used. Conditions of maintenance as well as exogenously given PL affected the transport of GABA. Two transport systems were observed, one first-order system and one cooperative system. Saturated species of PC or PE reduced first-order GABA uptake with increase in chain length of the fatty acid residues. The effects of unsaturated PL were dependent upon the polar head. Unsaturated PC enhanced the capacity of the first-order transport of the amino acid. In comparison to cultures grown in lipid-free medium, introduction of diarachinoyl-PC into the cells increased the density of the first-order active transport sites by a factor of 8 and the affinity constant by a factor of 17. Diarachinoyl-PE reduced both kinetic parameters. GABA uptake via the cooperative system was enhanced by the unsaturated PE, not by PC. The role of endogenous PL and their asymmetric distribution was studied by application of phospholipase A2, C, and D. Stimulation of carrier activity was induced by hydrolysis of PL on the external leaflet. Inhibition occurred upon enzymatic degradation of external and cytoplasmic PL. Lipolysis also affected GABA receptor binding, suggesting that the effects observed represent the activity of both classes of binding sites, the carrier and the receptor. However the latter accounted for a small fraction of the binding. Transport of the amino acid was temperature sensitive. The temperature curve was shifted within two discontinuities, appearing in the Arrhenius plot as a function of membrane lipids. The results suggest a partitioning of the proteins between fluid and ordered lipid domains. Displacement of the protein may govern the rate constants and/or the effective protein concentration.

Structure and immunological localization of spleen sulfolipid

By using chemical and immunological techniques, the structure of the spleen sulfolipid was confirmed as being a sulfogalactosylceramide. This lipid was localized in the spleen granulocytes (polymorphonuclear leukocytes).

Membrane lipids in bromodeoxyuridine-differentiated astroglial cells in culture

Embryonic hamster astroblasts (NN strain) grown in continuous line were cultivated in the presence of bromodeoxyuridine (BrdU). A decrease in the growth rate of the cells and striking changes in their morphology were observed, the morphology of the cells resembling that of mature astrocytes. Membrane lipids of BrdU-differentiated and standard cells were compared. No modification of the lipid/protein ratio was observed. Phospholipids and cholesterol were increased in the same proportions in the cells, and no modification of the phospholipid distribution was observed. Ganglioside sialic acid remained at the same level, but the ganglioside distribution was highly modified. Complex gangliosides appeared (GM1 and GD1a), while the proportion of simple gangliosides (GM3 and GD3) decreased. However, neither GT1 nor GQ1 were detected in differentiated cells. The distribution of phosphoglyceride acyl groups was highly modified, the proportion of arachidonic and docosapentaenoic acids being 2 to 3 times higher in BrdU-treated cells than in proliferating ones. These results were compared to those obtained with another clonal line of glial cells (C6) which exhibited no morphological differentiation in the presence of BrdU; the lipids of these cells were not modified by such a treatment.

Essential fatty acid metabolism in cultured astroblasts

The fetal calf serum on which two astroblast cell lines were grown was shown to be deficient in essential fatty acids. The fatty acid profiles of lipids of these two cell lines showed very low amounts of polyunsaturated fatty acids. In order to know if this low level of unsaturation was due to the lack of essential fatty acids in serum, or to a lack of desaturase activities in the cells, we have investigated the modifications of the cell lipid fatty acid patterns when serum was enriched in essential fatty acids. Linoleic acid was incorporated in rather high amounts in the cell lipids, while linolenic acid was very poorly incorporated. These two essential fatty acids were converted into polyunsaturated fatty acids only when they were added alone to the serum. Both cell clones exhibited a lack in the delta 4 desaturase activity. No morphological changes of the cells occured after nine days of culture with modified serum.