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PubMed1987

Effects of cholesterol sulfate on lipid metabolism in cultured human keratinocytes and fibroblasts.

Effects of cholesterol sulfate on acetate incorporation into lipid fractions were examined in normal human fibroblast and keratinocyte cultures. Inhibition of sterologenesis in normal fibroblast cultures by cholesterol sulfate was less profound than that produced by either lipoprotein-containing serum or 25-hydroxycholesterol. Cholesterol sulfate also inhibited sterologenesis in low density lipoprotein receptor-deficient fibroblasts and inhibited both sterologenesis and 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in keratinocytes. Cholesterol sulfate increased incorporation of acetate into fatty acid-containing lipids in preconfluent cultures of both cell types in lipoprotein-depleted media. Similar effects were not observed either in response to lipoprotein-containing serum or 25-hydroxycholesterol. Cholesterol sulfate had no effect on oleic acid incorporation into diglycerides, triglycerides, or phospholipid fractions; neither did it inhibit acid lipase activity; nor did it inhibit fatty acid oxidation, indicating that cholesterol sulfate does not inhibit catabolism of acyl lipids. Because cholesterol sulfate had similar effects on fatty acid metabolism in steroid sulfatase-deficient fibroblasts lines, desulfation to cholesterol is not a prerequisite. Cholesterol sulfate did not significantly affect incorporation of oleic acid into sterol esters in fibroblast cultures, but in contrast, inhibited sterol esterification in keratinocyte cultures. These data suggest a novel role for cholesterol sulfate as a modulator of cellular lipid biosynthesis.

Acetates↗
PubMed1989

Effect of dietary palm oils on mammary carcinogenesis in female rats induced by 7,12-dimethylbenz(a)anthracene.

Female Sprague-Dawley rats, 50 days of age, were treated with a single dose of 5 mg of 7,12-dimethylbenz(a)anthracene intragastrically. 3 days after carcinogen treatment, the rats were put on semisynthetic diets containing 20% by weight of corn oil (CO), soybean oil (SBO), crude palm oil (CPO), refined, bleached, deodorized palm oil (RBD PO) and metabisulfite-treated palm oil (MCPO) for 5 months. During the course of experiments, rats fed on different dietary fats had similar rate of growth. Rats fed 20% CO or SBO diet have higher tumor incidence than rats fed on palm oil (PO) diets; however differences of mean tumor latency periods among the groups were not statistically significant. At autopsy, rats fed on high CO or SBO diets had significantly more tumors than rats fed on the three PO diets. Our results showed that high PO diets did not promote chemically induced mammary tumorigenesis in female rats when compared to high CO or SBO diets. CO and SBO differ greatly from the palm oils in their contents of tocopherols, tocotrienols, and carotenes. But further experiments would be required to determine whether the observed differences in tumor incidence and tumor numbers were due to the differences in these minor components or due to the unique triglyceride structure of the palm oils. Analysis of the fatty acid profiles of plasma total lipids of tumor-bearing rats and of the tumor total lipids showed that, with the exception of arachidonic acid, the fatty acid profiles reflect the nature of the dietary fats. At autopsy, there were no differences in the plasma total cholesterol contents among rats fed on different dietary fats, but rats fed on palm oil diets had a significantly higher plasma triglyceride level than that of rats fed CO or SBO diets. As for the tumor lipids, there were no significant differences in the triglyceride, diglyceride, and phospholipid levels when the CO or SBO groups were compared to the palm oil groups.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1989

Phospholipid-stimulated protein kinase in plants.

In membrane fractions from zucchini (Cucurbita pepo L.) hypocotyls, catalytic properties of a platelet-activating factor (PAF)-activated protein kinase were investigated. In the presence of [ethylenebis(oxyethylenenitrilo)]tetraacetic acid, phosphorylation of a 55-kDa membrane polypeptide and, to a lesser extent, several others, including a 120-kDa polypeptide, was stimulated by PAF. The phosphorylation of the 55-kDa polypeptide was used for quantification of the PAF-stimulated protein kinase. Stimulation of protein phosphorylation by PAF increased in a concentration range from 10-200 micrograms/ml (= 19-380 microM) PAF up to 10-fold above the control. Addition of Ca2+ ions in the micromolar range in the presence and in the absence of PAF increased the phosphorylation of the 55- and the 120-kDa polypeptide. Other phospholipids and lipids tested including phorbol ester, diglyceride, mono- and triglyceride, and oleic acid were ineffective. The same lipid specificity was previously observed for the activation of ATP-dependent H+ transport in microsomes (Scherer, G.F.E., Martiny-Baron, G., and Stoffel, B. (1988) Planta 175, 241-253). Lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE) were able to stimulate the phosphorylation of the same polypeptides as PAF and H+ transport but both to a lesser extent (PAF greater than LPC greater than LPE). In the presence of EGTA, PAF-stimulated phosphorylation of a 55- and a 57-kDa polypeptide was predominantly associated with vacuolar membranes and those of 42, 61, 63, and 120 kDa were predominantly associated with plasma membranes. Stimulation of ATP-dependent H+ transport by PAF was found in tonoplast vesicles whereas plasma membrane vesicles had only little transport activity and, therefore, an effect of PAF on plasma membrane H+ transport could not be measured. Stimulation of ATP hydrolysis by PAF was observed both in tonoplast- and plasma membrane-containing fractions.

Adenosine Triphosphatases↗
PubMed1989

Chemoattractant-induced cytoplasmic pH changes and cytoskeletal reorganization in human neutrophils. Relationship to the stimulated calcium transients and oxidative burst.

The relationships between the chemotactic factor-stimulated mobilization of calcium, activation of the NADPH-oxidase, changes in cytosolic pH, and in the level of polymerized actin in human neutrophils have been examined. The approach taken was to use intracellular calcium chelators, and pharmacologic modulators (both positive and negative) of the NADPH-oxidase to measure the aforementioned responses under conditions where the calcium transients were abrogated and/or the generation of superoxide anions was either inhibited or augmented. The decrease in cytosolic pH induced by chemoattractants was inhibited by the calcium chelator BAPTA and by the diglyceride kinase inhibitor 6-[2-(4-[(4-fluorophenyl)phenylmethylene]-1-piperidinylethyl ]-7-methyl-5H-thiazolo[3,2-alpha]pyriimidin-5-one (R59022) (this latter compound enhanced the oxidative response of the cells). Furthermore, a specific inhibitor of the NADPH-oxidase (diphenyleneiodonium) had no significant effect on the cytosolic acidification induced by FMLP or leukotriene B4. These results indicate that the initiation of the cytosolic acidification induced by chemotactic factors is a calcium-dependent event that is not directly linked to the activation of the NADPH-oxidase. In contrast, the stimulated polymerization of actin was insensitive to BAPTA, R59022, and diphenyleneiodonium. Thus, neither the calcium transients nor the oxidative burst play a signaling role in the initiation of actin polymerization elicited by chemoattractants. These data indicate that additional investigations are needed to uncover the biochemical basis of the signals initiated in human neutrophils by chemotactic factors that lead to the polymerization of actin and to the cytosolic acidification.

Actins↗
PubMed1989

Neutrophil cathepsin G increases calcium flux and inositol polyphosphate production in cultured endothelial cells.

Exposure of endothelial cells (ENDO) to human neutrophil cathepsin G (CG) increases albumin flux across the endothelial monolayer. Since calcium influences cell shape and barrier function of ENDO monolayers, the current study was designed to determine if CG acted through alterations in Ca2+ homeostasis in ENDO. The role of Ca2+ in the increased permeability of ENDO monolayers to albumin after exposure to CG was studied by using ENDO monolayers cultured on polycarbonate filters. Exposure of ENDO monolayers to CG in the presence of the Ca2+-antagonist lanthanum partially prevented the increase in albumin flux, but exposure in the presence of agents that block voltage-regulated calcium channels did not block the increase in albumin flux. To monitor the effect of CG on Ca2+-flux, ENDO were labeled with 45Ca2+ and changes in Ca2+ flux were monitored by the release of 45Ca2+. From 1 to 15 minutes after exposure of ENDO to CG, there was increased release of 45Ca2+ compared with control cells. Calcium channel blocking agents did not inhibit the increased release of 45Ca2+, but lanthanum partially blocked the increase. The increased release of Ca2+ appeared to be due, at least in part, to activation of phospholipase C because there was an increase both in inositol polyphosphate species and in diglycerides after incubation of ENDO with CG. These studies support the hypothesis that CG increases the flux of calcium in ENDO, that this increase in Ca2+ flux may result from activation of phospholipase C, and that this system may be involved in the decreased barrier properties of the ENDO after CG exposure.

Albumins↗
PubMedDate not supplied

[Anabolic effects of sodium selenite, vitamin E and retabolil in experimental hypotrophy induced by a pesticide].

Forty Chinchilla rabbits of both sexes were examined for changes in some parameters of protein, lipid and trace elements metabolism (total protein, protein fractions, urea, residual nitrogen in blood serum, lipids, total cholesterol, free cholesterol, diglycerides, phospholipids, triglycerides, free fatty acids and the trace elements selenium, iron, zinc and so forth in the liver) during the animals' poisoning with the defoliant magnesium chlorate. A study was made of the effect on these changes of the administration for 3 weeks of sodium selenite (15 micrograms/kg), vitamin E (25 mg/kg) and retabolil (2 mg/kg once a week). It has been established that the combined administration of these agents removes and prevents the changes in protein, lipid and trace elements (hypoproteinemia, dysproteinemia and impairment of the nitrous balance) and lipid metabolism because of the animals' poisoning with magnesium chlorate.

Anabolic Agents↗
PubMed1988

Exogenous oxidants initiate hydrolysis of endothelial cell inositol phospholipids.

Oxidants released from inflammatory cells contribute to the pathogenesis of acute inflammatory edema in many models. Chemically produced oxidants can reversibly alter the barrier properties of cultured endothelial and epithelial monolayers. This report examines the effects of nonlytic doses of H2O2 on endothelial cell lipids. H2O2 oxidized omega-6 fatty acids in the endothelial cells and initiated hydrolysis of endothelial cell phospholipids. When endothelial cells were exposed to peroxidized linoleic acid, it caused lysis of the cells at doses 1,000-fold lower than effective doses of H2O2. The phospholipid hydrolysis was directed primarily at the inositol phospholipids and consisted of both A and C type phospholipase activity. The phospholipase A hydrolysis resulted in increases in endothelial cell free fatty acids and lysophosphatidylinositol. The phospholipase C hydrolysis resulted in increases in diglycerides, phosphatidic acid, and inositol polyphosphate levels. The phospholipase C hydrolysis of phosphatidylinositol is known to activate protein kinase C in most cells. Stimulation of protein kinase C with phorbol-12,13-dibutyrate increased albumin flux across endothelial monolayers and altered endothelial cell shape, similar to effects of oxidants. These data are consistent with the hypothesis that oxidant-initiated hydrolysis of endothelial cell inositol phospholipids contributes to oxidant-mediated reversible changes in endothelial monolayer barrier function.

Animals↗
PubMed1985

Platelet metabolism and activation.

Stimulation and execution of platelet responses are intimately coupled to the cells' energy metabolism. The turnover of cytoplasmic ATP is higher than in most other cells; when it is lowered, platelet responses are powerfully inhibited. One-third of the total adenine nucleotides are present in the cytoplasm and a small fraction of these, 50% of the ADP, is bound to actin and not available to metabolism. These nucleotides are not synthesized de novo in platelets which readily form them from adenine, adenosine, and hypoxanthine. The remaining two-thirds are sequestered in the dense granules together with serotonin and divalent metal ions. NMR studies show that this ATP and ADP are stacked in large aggregates together with the divalent cations. Serotonin is incorporated into the aggregates by being positioned between, and in close proximity to, adjacent adenine rings. In the congenital platelet disorder, "Storage Pool Deficiency," the dense granule content is absent or markedly reduced, which may be caused by an impaired transport of ATP across the dense granule membrane. The content of the dense granules, the beta-thromboglobulin, albumin, fibrinogen, certain coagulation factors, fibronectin of the alpha-granules, and the acid hydrolases of the lysosomes are discharged by exocytosis, but the exact mechanisms are not known. This discharge, platelet secretion, is complete for the dense granule and alpha-granules contents, but is only 30% to 55% for the acid hydrolases. After pretreatment of platelets with certain amines, thrombin causes secretion of all beta-hexosaminidase, indicating that the beta-hexosaminidase usually retained during secretion is bound within the lysosomes at the acid pH but becomes dissociated by raising the pH with the amines. Agonist-induced platelet aggregation and secretion are accompanied by rapid changes in phosphoinositide metabolism which are usually monitored as the radioactivity in phospholipids of platelets preincubated with radioactive arachidonate, glycerol, inositol, or orthophosphate. The mechanisms for precursor incorporation are not well known and interpretations of published results are hampered by much uncertainty. Experimental support for the widely accepted coupling of receptor occupancy to the phosphodiesteratic hydrolysis of phosphatidylinositol or phosphatidylinositol-4,5-biphosphate is nonexistent. These two hydrolytic steps occur concomitantly and together with formation of diglyceride and phosphatidate; all four steps cannot be temporally resolved.(ABSTRACT TRUNCATED AT 400 WORDS)

Actins↗
PubMed1985

Calcium mobilization and signal transduction in the neutrophils.

Neutrophil responsiveness is initiated by increases in the intracellular concentration of calcium through mechanisms the elucidation of which is of interest to the field of signal transduction in calcium mobilizing systems. Some, but not all, neutrophil chemotactic factors specifically stimulate the hydrolysis of phosphatidylinositol 4,5-bisphosphate. A non-mitochondrial pool of internal calcium has been shown to be released in permeabilized cells by inositol 1,4,5-trisphosphate. Diglyceride is thought to activate protein kinase C producing stimulatory and inhibitory signals for neutrophil activation. The lack of effect of leukotriene B4, on polyphosphoinositide hydrolysis indicates that mechanisms independent of inositol 1,4,5-trisphosphate are also available to the neutrophils. Pertussis toxin inhibits the stimulated mobilization of calcium, hydrolysis of the polyphosphoinositides and activation of protein kinase C. The inhibitory effects of pertussis toxin can be bypassed by phorbol esters and calcium ionophores thus indicating that a guanine nucleotide binding protein is functionally located at a step preceding the activation of phospholipase C. The similarities between the biochemical events activated by chemotactic factors and those described in other hormonally sensitive cells emphasize the generality of the relevance of these concepts. The differences raise the possibility that elements of the excitation-response coupling sequence other than those commonly monitored will still be identified. The later may be more evident in the neutrophils because these cells' predominant function is motility and not secretion.

Calcium↗
PubMed1986

Isolation and characterization of the inositol cyclic phosphate products of phosphoinositide cleavage by phospholipase C. Metabolism in cell-free extracts.

The phosphoinositides are metabolized by phospholipase C in response to hormone or agonist stimulation in many cell types to produce diglyceride and water-soluble inositol phosphates. We have recently shown that the phospholipase C reaction products include cyclic phosphate esters of inositol. One of these, inositol 1, 2-cyclic 4,5-trisphosphate, is active in promoting Ca2+ mobilization in platelets and in inducing changes in conductance in Limulus photoreceptors similar to those produced by light (Wilson, D. B., Connolly, T. M., Bross, T. E., Majerus, P. W., Sherman, W. R., Tyler, A., Rubin, L. J., and Brown, J. E. (1985) J. Biol. Chem. 260, 13496-13501. In the current study, we have examined the metabolism of the inositol phosphates. We find that both cyclic and non-cyclic inositol trisphosphates are metabolized by inositol 1,4,5-trisphosphate 5-phosphomonoesterase, to inositol 1,2-cyclic bisphosphate and inositol 1,4-bisphosphate, respectively. However, the apparent Km of the enzyme for the cyclic substrate is approximately 10-fold higher than for the non-cyclic substrate. These inositol bisphosphates are more slowly degraded to inositol 1,2-cyclic phosphate and inositol 1-phosphate, respectively. Inositol 1,2-cyclic phosphate is then hydrolyzed to inositol 1-phosphate, which in turn is degraded to inositol and inorganic phosphate by inositol 1-phosphate phosphatase. The human platelet inositol 1,2-cyclic phosphate hydrolase enzyme and a similar rat kidney hydrolase do not utilize the cyclic polyphosphate esters of inositol as substrates. These results suggest that the inositol cyclic phosphates and the non-cyclic inositol phosphates are metabolized separately by phosphatases to cyclic and non-cyclic inositol monophosphates. The cyclic monophosphate is then converted to inositol 1-phosphate by a cyclic hydrolase. We suggest that the enzymes that metabolize the inositol phosphates may serve to regulate cellular responses to these compounds.

Animals↗
PubMed1986

Stimulated platelets release equivalent amounts of arachidonate from phosphatidylcholine, phosphatidylethanolamine, and inositides.

Thrombin-induced changes in arachidonate content of platelet phospholipids were quantitated to establish the ultimate origins of this eicosanoid precursor. Fifteen seconds following thrombin addition (15 U/5 X 10(9) platelets), phosphatidylcholine lost 11.8 nmol of arachidonate and phosphatidylethanolamine lost 10.5 nmol. Arachidonate in phosphatidate, phosphatidylinositol, and phosphatidylinositol-4,5-bisphosphate combined decreased by 11.0 nmol. Increases in free and oxygenated arachidonate (41 nmol) exceeded decreases in inositides. Thus phospholipase A2 released at least twice as much arachidonate as phospholipase C-diglyceride lipase. Phosphatidylinositol-4-phosphate levels remained unchanged upon stimulation. Therefore, increases in phosphatidylinositol-4,5-bisphosphate indicated the minimum rate of phosphorylation of phosphatidylinositol to resynthesize phosphatidylinositol-4,5-bisphosphate, following stimulus-induced breakdown by phospholipase C. Phosphatidylinositol-4, 5-bisphosphate increased 1.4 nmol between 10 and 15 sec following thrombin, markedly less than phosphatidylinositol decreased (2.1 nmol). This could be due to phospholipase A2, in addition to phospholipase C, acting directly on phosphatidylinositol to a greater extent than estimated by accumulation of lysophosphatidylinositol, degraded rapidly by lysophospholipase. Thus, upon high-dose thrombin stimulation of human platelets inositide metabolism via phospholipase C directs initial formation of intracellular second messengers, and sequentially, or in parallel, arachidonate release by phospholipase A2 supplies the larger proportion of arachidonate for syntheses of eicosanoids involved in intercellular communication.

Arachidonic Acid↗
PubMedDate not supplied

Alterations in phospholipid biosynthesis by polychlorinated biphenyls and polychlorinated biphenylols.

Inhibition and stimulation of synthesis of phospholipids by polychlorinated biphenyls (PCB) have been reported by several authors. The mode of action of PCB on the synthesis of phospholipids has not been determined. Results of experiments in the present report indicate that both PCB and polychlorinated biphenylols alter the activities of key enzymes of glyceride and phospholipid synthesis. 4-Chloro-4-biphenylol (CB-OH), 2',3',4',5,5'-pentachlorobiphenylol (PCB-OH) and 2,4,5,2',4',5'-hexachlorobiphenyl (HCB) inhibited sn-glycerol-3-phosphate acyltransferase activity. Inhibition by PCB-OH was noncompetitive with apparent Ki of 2.6 X 10(-4) M. PCB-OH stimulated phosphatidase activity, but no apparent change was observed with CB-OH. PCB inhibited phosphorylcholine glyceride transferase activity, but had no significant effect on diglyceride acyl transferase.

Acyltransferases↗
PubMed1987

The biosynthesis of gram-negative endotoxin. A novel kinase in Escherichia coli membranes that incorporates the 4'-phosphate of lipid A.

Extracts of Escherichia coli contain an enzyme that generates the beta,1----6 linkage of lipid A from fatty-acylated monosaccharide precursors, according to the reaction: 2,3-diacyl-GlcN-1-P + UDP-2,3-diacyl-GlcN----2,3-diacyl-GlcN (beta, 1----6)2,3-diacyl-GlcN-1-P + UDP (Ray, B. L., Painter, G., and Raetz, C. R. H. (1984) J. Biol. Chem. 259, 4852-4859). We now describe a membrane-bound kinase that phosphorylates the 4'-position of the above tetraacyldisaccharide 1-phosphate product. The lipid A 4'-kinase is distinct from the diglyceride kinase of E. coli. When crude membrane preparations are employed, several nucleoside triphosphates are able to support the phosphorylation of the tetraacyldisaccharide 1-phosphate, but ATP is the most efficient. The 4'-kinase requires Mg2+ and is stimulated by phospholipids, especially cardiolipin. Under optimal conditions the specific activity in crude extracts is 0.5 nmol/min/mg. The enzyme is rapidly inactivated by preincubation in the presence of detergents, such as Nonidet P-40 or octylglucoside, but phosphoenolpyruvate and glycerol stabilize the enzyme. The product generated in vitro has been characterized by fast atom bombardment mass spectrometry and by 1H and 31P NMR spectroscopy. Those analyses confirm that the 4' hydroxyl is the site of phosphorylation. The 4'-kinase reported here is likely to represent a key step in the de novo biosynthesis of lipid A.

Adenosine Triphosphate↗
PubMed1987

Preferential synthesis of diacyl and alkenylacyl ethanolamine and choline glycerophospholipids in rabbit platelet membranes.

In rabbit platelet membranes, the contents of alkenylacyl phospholipids (plasmalogen) were 56% of phosphatidylethanolamine and 3% of phosphatidylcholine. This uneven distribution of plasmalogens in each phospholipid class could be attributed to the different substrate specificity of ethanolaminephosphotransferase (EC 2.7.8.1) and cholinephosphotransferase (EC 2.7.8.2). The properties of the enzymes were studied, using endogenous diglycerides and CDP-[3H]ethanolamine or CDP-[14C]choline as substrates. The newly formed phospholipids were mainly diacyl and alkenylacyl and only rarely alkylacyl type. The ratios of the labeled alkenylacyl to diacyl type of phospholipids clearly varied with the concentrations of CDP-ethanolamine or CDP-choline. When 1, 10, and 30 microM CDP-[3H]ethanolamine were used, the labeled phospholipids contained 53, 37, and 27% of the alkenylacyl type, respectively. The apparent Km for CDP-ethanolamine to synthesize alkenylacyl and diacyl types were 2.2 and 8.1 microM. On the other hand, when 1, 10, and 30 microM CDP-[14C]choline were used, the labeled lipids contained 10, 17, and 24% alkenylacyl type, respectively. The apparent Km for CDP-choline to synthesize alkenylacyl and diacyl types were 24 and 4.3 microM. Further, the syntheses of diacyl type of phosphatidylethanolamine and the alkenylacyl type of phosphatidylcholine were markedly inhibited by unlabeled CDP-choline and CDP-ethanolamine, respectively. The two enzymes had opposite substrate specificities, and ethanolaminephosphotransferase showed a high preference to plasmalogen synthesis, especially in the presence of CDP-choline.

Animals↗
PubMed1987

Regulation by phosphatidylinositol of rat pituitary plasma membrane and endoplasmic reticulum phosphatidylinositol synthase activities. A mechanism for activation of phosphoinositide resynthesis during cell stimulation.

The mechanism of signal transduction used by a large number of extracellular regulatory molecules involves hydrolysis and resynthesis of phosphoinositides. We recently demonstrated that during stimulation by thyrotropin-releasing hormone of rat pituitary (GH3) cells phosphatidylinositol (PtdIns) resynthesis occurs within the plasma membrane as well as the endoplasmic reticulum (Imai, A., and Gershengorn, M. C. (1987) Nature, 325, 726-728). In this report, we have studied regulation of PtdIns synthase (CDP-diglyceride-inositol phosphatidyltransferase, EC 2.7.8.11) activities associated with plasma membranes and endoplasmic reticulum isolated from GH3 cells. Exogenously added PtdIns noncompetitively inhibited membrane-associated and solubilized PtdIns synthase activities by up to 84 to 91%; half-maximal inhibition occurred between 0.03 and 0.1 mM PtdIns. Similar inhibition of PtdIns synthase activities were observed when PtdIns content of both membrane fractions was increased in vivo in intact GH3 cells prior to assay in vitro. These findings demonstrate that PtdIns synthase activities associated with plasma membrane and endoplasmic reticulum fractions isolated from GH3 cells are inhibited by the product, PtdIns. Because PtdIns levels decrease and PtdIns resynthesis is activated in both membrane fractions during stimulation of GH3 cells by thyrotropin-releasing hormone, it seems likely that activation of PtdIns synthase(s) during cell stimulation occurs by release of this enzyme(s) from inhibition by its product.

Animals↗
PubMed1987

Transduction of signals in the activation of T lymphocytes: relation to leukemia.

The biochemical events initiated by mitogen in T lymphocytes are the subject of this paper. Following interaction of the mitogen with its receptors, a transmembrane 'trigger-type' signal is propagated which has both positive and negative correlates. The negative signal occurs with high mitogen concentrations and is associated with membrane freezing, microtubular aggregation, receptor capping, adenylate cyclase activation, and cellular cyclic AMP increases. The positive signal occurs with optimal mitogen concentrations and is associated with changes in membrane permeability and transport with influx of calcium and potassium ion and efflux of sodium, in transport processes for glucose, amino acids, and nucleosides, and in a collected series of early membrane lipid changes which can be considered essential for the positive signal. These lipid changes include the uptake of arachidonic acid and other fatty acids, choline, phosphate and other molecules, their incorporation into membrane phospholipids, particularly phosphatidylinositol (PI), and a turnover of PI with the production of inositol triphosphate, which can be related to calcium mobilization and diacylglycerol which activates a cytoplasmic protein kinase C. A key event associated with mitogen action is arachidonic acid release. Arachidonic acid may give rise to prostaglandins and thromboxanes as part of negative components of the signal through effects on the adenylate cyclase/cyclic AMP system. Arachidonic acid gives rise to eicosanoids like 5-, 11-, possibly 12- and 15-hydroxyperoxy and hydroxy eicosatetraenoic acids and leukotrienes B4 and C4. The activation of the 5-lipoxygenase, a critical calcium-dependent step, leads via the production of 5-HPETE and 5-HETE to the activation of membrane and soluble guanylate cyclase and the production of cyclic GMP. Cyclic GMP appears to be essential for mitogen activation and is associated with cyclic GMP-dependent protein kinase activation and the phosphorylation of a number of substrates. Calcium ion influx is clearly central to mitogen action. Calcium through its influx and mobilization from cellular stores is thought to contribute directly and indirectly through the action of calmodulin and protein kinase C to the activation of a number of enzymatic processes involved in the positive signal including phospholipase C, diglyceride kinase and lipase, 5-lipoxygenase, and guanylate cyclase. Cyclic GMP and calcium ion both participate in nuclear processes leading to RNA and protein synthesis. Interleukin 2 is associated with midcycle increases in cyclic GMP and entry into DNA synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium↗
PubMed1986

Metabolic response of polymorphonuclear leukocyte to arachidonic and linoleic acids.

Various stimuli act on polymorphonuclear leukocytes (PMN), activating membrane-bound phospholipase A2 and C, and diglyceride lipase and then liberating unsaturated fatty acids (USFAs). These liberated USFAs are immediately metabolized through various metabolic pathways such as cyclooxygenase, lipoxygenase, phosphatidylinositol metabolism etc. It is possible that the metabolic intermediates of these pathways reveal various physiological actions. This work was undertaken to clarify whether stimuli on PMN depend on these USFAs themselves or on their oxidation products. The following results were obtained: 1. USFAs such as arachidonate and linoleate stimulate PMN, accelerating superoxide (O2) generation, depolarization of membrane potential and increase in [Ca2+]i. 2. Oxidation products of USFAs have no stimulative effect on PMN. The decrease in the stimulative effect of these USFAs following their oxidation is proportional to the quantitative decrease in non-oxidized linoleate. 3. USFAs accelerate membrane permeability of Ca2+, and their oxidation products enhance non-specific membrane permeability in proportion to the formation of monohydroxy compound. These results suggest that stimulative effects of USFAs on PMN do not depend on their oxidation products but on unoxidized fatty acids. Furthermore, among the oxidation products of the USFAs, monohydroxy compound acts as a strong perturber of membrane and accelerates membrane permeability.

Arachidonic Acid↗
PubMed1987

Transport and metabolism of extracellular free fatty acids in adipose tissue of fed and fasted mice.

We used a new tracer technique, direct tracer injection of [1-14C]palmitate-serum albumin into extracellular fluid (ECF) of epididymal fat pads, to study relative transport rates of ECF-free fatty acids (FFA) to cell-FFA and subsequent esterification to diglyceride fatty acid (DGFA) and triglyceride fatty acid (TGFA) in adipose tissue versus movement of ECF- and cell-FFA into the circulation of mice fed ad libitum or fasted 48 hr. Radioactivity was measured in the following fractions at varying times (for 1 hr): ECF-FFA, cell-FFA, cell-DGFA, cell-TGFA, plasma-FFA (total lipids), and breath CO2. Pool sizes of ECF-FFA, cell-FFA, cell-TGFA, and plasma-FFA were determined. Analysis by multicompartmental methods (SAAM) indicates that the ECF-FFA compartment of epididymal fat pads is in a relatively rapid exchange with a cellular-FFA compartment, but neither is in direct, nor appreciably rapid, communication with circulating FFA. FFA is rapidly esterified in adipocytes of fed mice, but esterification is significantly inhibited in mice fasted for 48 hr. In both dietary states, essentially all labeled FFA appearing in the circulation was derived from ECF-FFA that were first transferred to the cell, esterified to TGFA, then hydrolyzed to FFA before being transported to the circulation.

Adipose Tissue↗