scholarly journals Effect of insulin, catecholamines and calcium ions on phospholipid metabolism in isolated white fat-cells

1980 ◽  
Vol 186 (3) ◽  
pp. 781-789 ◽  
Author(s):  
J. Adolfo García-Sáinz ◽  
John N. Fain
Keyword(s):  
Fatty Acids ◽  
Phosphatidic Acid ◽  
Inhibitory Effect ◽  
Phospholipid Metabolism ◽  
Ionophore A23187 ◽  
Fat Cells ◽  
Adrenergic Stimulation ◽  
White Fat ◽  
Adrenergic Activation ◽  
Rat Fat Cells

The incorporation of [32P]Pi into phosphatidylinositol by rat fat-cells was markedly increased in the presence of adrenaline. Phosphatidic acid labelling was also increased, but to a lesser extent. These effects are due to α1-adrenergic stimulation since they were unaffected by propranolol, blocked by α-blockers in the potency order prazosin«phentolamine<yohimbine and mimicked by methoxamine. The α-adrenergic stimulation of phosphatidylinositol labelling did not require extracellular Ca2+, which supports the hypothesis that an increased turnover of phosphatidylinositol is involved in α-adrenergic activation of Ca2+ entry. Insulin and the ionophore A23187 gave a small increase in 32P labelling of phosphatidylinositol in Ca2+-free medium containing 1mm-EGTA. The increases due to insulin or ionophore A23187 were abolished if 2.5mm-Ca2+ was added to medium containing EGTA. However, the increases in labelling of phosphatidylinositol due to α-adrenergic amines were still evident in medium containing EGTA and Ca2+. Lipolytic agents such as corticotropin, dibutyryl cyclic AMP, adrenaline in the presence of phentolamine and isoproterenol decreased [32P]Pi incorporation into phosphatidylinositol, phosphatidylethanolamine and phosphatidic acid. This inhibitory effect may be secondary to accumulation of intracellular unesterified fatty acids, since it was decreased by incubating fewer cells in medium with 6 rather than 3% albumin and was restored by the addition of oleate to the medium. The incorporation of [32P]Pi into phosphatidylcholine was unaffected by lipolytic agents. The data suggest that there is an inhibition of the synthesis of certain phospholipids in the presence of lipolytic agents, which may be secondary to intracellular accumulation of unesterified fatty acids.

scholarly journals Evidence for the calcium-dependent activation of phospholipase D in thrombin-stimulated human erythroleukaemia cells

1990 ◽  
Vol 267 (2) ◽  
pp. 479-483 ◽  
Author(s):  
S P Halenda ◽  
A G Rehm
Keyword(s):  
Phosphatidic Acid ◽  
Phospholipase C ◽  
Phospholipase D ◽  
Calf Serum ◽  
Platelet Activating Factor ◽  
Diacylglycerol Kinase ◽  
Sole Source ◽  
Phospholipid Metabolism ◽  
Ionophore A23187 ◽  
Hel Cells

Human erythroleukaemia (HEL) cells were exposed to thrombin and other platelet-activating stimuli, and changes in radiolabelled phospholipid metabolism were measured. Thrombin caused a transient fall in PtdInsP and PtdInsP2 levels, accompanied by a rise in diacylglycerol and phosphatidic acid, indicative of a classical phospholipase C/diacylglycerol kinase pathway. However, the rise in phosphatidic acid preceded that of diacylglycerol, which is inconsistent with phospholipase C/diacylglycerol kinase being the sole source of phosphatidic acid. In the presence of ethanol, thrombin and other agonists (platelet-activating factor, adrenaline and ADP, as well as fetal-calf serum) stimulated the appearance of phosphatidylethanol, an indicator of phospholipase D activity. The Ca2+ ionophore A23187 and the protein kinase C activator phorbol myristate acetate (PMA) also elicited phosphatidylethanol formation, although A23187 was at least 5-fold more effective than PMA. Phosphatidylethanol production stimulated by agonists or A23187 was Ca2(+)-dependent, whereas that with PMA was not. These result suggest that phosphatidic acid is generated in agonist-stimulated HEL cells by two routes: phospholipase C/diacylglycerol kinase and phospholipase D. Activation of the HEL-cell phospholipase D in response to agonists may be mediated by a rise in intracellular Ca2+.

scholarly journals Selective mobilization of fatty acids from white fat cells: evidence for a relationship to the polarity of triacylglycerols

1997 ◽  
Vol 322 (2) ◽  
pp. 483-489 ◽  
Author(s):  
Thierry RACLOT
Keyword(s):  
Fatty Acids ◽  
Adipose Tissue ◽  
Fatty Acid ◽  
Chain Length ◽  
Wide Spectrum ◽  
Fat Cells ◽  
Double Bonds ◽  
Fat Cell ◽  
Relative Enrichment ◽  
White Fat

Fatty acids are selectively released from white fat cells in accordance with well-defined rules relating their molecular structure and their mobilization rate, emphasizing the possible role of their physicochemical properties. Lipolysis is widely reported to work for conditions where only small amounts of substrate are available. We hypothesize that the preferential hydrolysis of a substrate fraction enriched in the most polar triacylglycerols (TAGs) reflects the pattern of selective fatty acid mobilization. Rat adipose tissue was first manipulated by dietary means to obtain a wide spectrum of fatty acids. Fat cell TAGs were separated into eight fractions according to polarity by liquid–liquid partition chromatography and their fatty acid proportions and compositions were determined by GLC. In the most polar TAG fractions, the relative enrichment of fatty acids (percentage in a TAG fraction divided by percentage in total TAGs) increased with the number of double bonds for a given chain length, whereas it decreased with increasing chain length for a given degree of unsaturation. The relative enrichment of highly mobilized fatty acids (16–20 carbon atoms and four or five double bonds) was very high (more than 2.5) in the most polar TAG fractions, whereas that of weakly mobilized fatty acids (20–24 carbon atoms and no or one double bond) was very low (less than 0.5). The relative enrichment of moderately mobilized fatty acids (comprising all the others) was close to unity. Our study shows that the relative enrichment of fatty acids in the most polar adipose tissue TAGs is consistent with their relative mobilization rates. This supports our hypothesis and raises the possibility that the molecular species of TAGs might be one of the regulating factors.

scholarly journals Inositol phospholipid metabolism and myoblast fusion

1983 ◽  
Vol 214 (1) ◽  
pp. 77-82 ◽  
Author(s):  
M J O Wakelam
Keyword(s):  
Tissue Culture ◽  
Phosphatidic Acid ◽  
Phospholipid Metabolism ◽  
Myoblast Fusion ◽  
Ionophore A23187 ◽  
Rapid Synthesis ◽  
Inositol Phospholipid

The fusion of chick embryonic myoblasts has been studied in tissue culture. Myoblasts are maintained at 0.1 microM-Ca2+ for 50 h. During this time they achieve fusion competence. Fusion is initiated by raising the medium Ca2+ concentration to 1.4 mM. A rapid breakdown of the polyphosphoinositides was detected within 3 min of Ca2+ addition. Rapid synthesis of phosphatidic acid was also detected at this time. Breakdown of phosphatidylinositol and synthesis of 1,2-diacylglycerol were also detected. Other phospholipids were unaffected. Sr2+ could replace Ca2+ in this process but Mg2+ could not and also inhibited the Ca2+ effect. The Ca2+-ionophore A23187 stimulated further apparent polyphosphoinositide breakdown in the presence of Ca2+. 6. The results are discussed with respect to myoblast fusion.

scholarly journals The action of local anaesthetics on lipolysis and on adenosine 3′:5′-cyclic monophosphate content in isolated rat fat-cells

1974 ◽  
Vol 142 (2) ◽  
pp. 345-351 ◽  
Author(s):  
Kenneth Siddle ◽  
C. Nicholas Hales
Keyword(s):  
Cyclic Amp ◽  
Glucose Uptake ◽  
Local Anaesthetics ◽  
Inhibitory Effect ◽  
Fat Cells ◽  
Atp Content ◽  
Dibutyryl Cyclic Amp ◽  
Ion Movements ◽  
Rat Fat Cells ◽  
Isolated Rat

1. Local anaesthetics inhibited hormone-stimulated lipolysis in isolated rat fat-cells. The most potent anaesthetic was dibucaine, which inhibited adrenaline-stimulated lipolysis by 50% at a concentration of 0.16mm. 2. The amount of inhibition produced by a given concentration of anaesthetic was very similar with adrenaline, theophylline and dibutyryl cyclic AMP, at submaximal and maximal concentrations. 3. The inhibitory effect of dibucaine on lipolysis was apparent within 5 min and was constant over 1h. 4. Dibucaine inhibited basal, adrenaline-stimulated and insulin-stimulated glucose uptake at concentrations 6–10-fold higher than those inhibiting lipolysis. 5. The effects of dibucaine on lipolysis and glucose uptake were reversed after removal of anaesthetic and washing of cells. 6. Dibucaine further elevated the concentration of cyclic AMP in the presence of adrenaline or adrenaline plus theophylline. 7. Dibucaine had no effect on ATP content at concentrations causing 80% inhibition of lipolysis, but lowered ATP content at higher concentrations. 8. The relative potency of different local anaesthetics as inhibitors of hormone-stimulated lipolysis paralleled their potency as inhibitors of ion movements in other systems. 9. The possibility is discussed that Ca2+ions are involved in the regulation of lipolysis, and that local anaesthetics inhibit lipolysis by interfering with Ca2+translocation.

scholarly journals Lipogenesis in rat and guinea-pig isolated epididymal fat-cells

1974 ◽  
Vol 140 (2) ◽  
pp. 211-224 ◽  
Author(s):  
E. David Saggerson
Keyword(s):  
Fatty Acids ◽  
Guinea Pig ◽  
Malate Dehydrogenase ◽  
Isocitrate Dehydrogenase ◽  
Aspartate Aminotransferase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Fat Cells ◽  
Hexose Monophosphate ◽  
Hexose Monophosphate Pathway ◽  
Rat Fat Cells

Fat-cells were prepared from rat and guinea-pig epididymal adipose tissue and compared on the basis of the intracellular distributions and activities of enzymes and with respect to their utilization of various U-14C-labelled substrates for lipogenesis. 1. Compared with the rat, guinea-pig extramitochondrial enzyme activities differed in that aconitate hydratase, alanine aminotransferase, ATP–citrate lyase, lactate dehydrogenase, NAD–malate dehydrogenase, NADP–malate dehydrogenase and phosphoenolpyruvate carboxykinase activities were appreciably lower, whereas aspartate aminotransferase, glucose 6-phosphate dehydrogenase, NADP–isocitrate dehydrogenase and 6-phosphogluconate dehydrogenase activities were appreciably higher. Mitochondrial activities of citrate synthase, NADP–isocitrate dehydrogenase and pyruvate carboxylase were appreciably lower, whereas mitochondrial activities of aspartate aminotransferase, glutamate dehydrogenase, NAD–malate dehydrogenase and phosphoenolpyruvate carboxykinase were higher in the guinea pig compared with the rat. 2. In general guinea-pig fat-cells incorporated acetate and lactate into fatty acids more readily than rat fat-cells, whereas rat fat-cells incorporated glucose and pyruvate more readily than guinea-pig fat-cells. 3. Acetate stimulated the incorporation of glucose into fatty acids in rat fat-cells, but had no appreciable effect upon this process in guinea-pig fat-cells. Acetate greatly decreased the incorporation of lactate into fatty acids in cells from both species. 4. Lactate/pyruvate ratios produced by incubation of guinea-pig cells with glucose+insulin were very low compared with those found with rat cells under the same conditions. 5. With glucose (+insulin) or with glucose+acetate (+insulin) as substrates guinea-pig cells produced enough NADPH by the hexose monophosphate pathway to satisfy the NADPH requirements of lipogenesis. In rat fat-cells under the same conditions, hexose monophosphate-pathway NADPH provision was not sufficient to meet the requirements of lipogenesis. 6. These results are discussed, particularly in relationship to the disposition of cytosolic reducing equivalents in the cells.

scholarly journals α1-Adrenergic stimulation of Ca2+ mobilization without phosphorylase activation in hepatocytes from phosphorylase b kinase-deficient gsd/gsd rats

1981 ◽  
Vol 198 (2) ◽  
pp. 379-383 ◽  
Author(s):  
P F Blackmore ◽  
J H Exton
Keyword(s):  
Strong Evidence ◽  
Liver Cells ◽  
Ionophore A23187 ◽  
Adrenergic Stimulation ◽  
Bivalent Cation ◽  
Site Of Action ◽  
Adrenergic Activation ◽  
Stimulation Of

Phenylephrine, vasopressin and the bivalent cation ionophore A23187 mobilized Ca2+ normally, but failed to activate phosphorylase, in hepatocytes from gsd/gsd rats with a deficiency of liver phosphorylase b kinase. These data provide strong evidence that phosphorylase b kinase is the site of action of the Ca2+ mobilized intracellularly during alpha 1-adrenergic activation of phosphorylase in liver cells.

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