The effects of orthovanadate on fatty acid synthesis in isolated rat hepatocytes.
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ABSTRACT:
SUBMITTER: Agius L
PROVIDER: S-EPMC1158177 | biostudies-other | 1982 Mar
REPOSITORIES: biostudies-other
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Project description:We studied the influence of glucose/glucose 6-phosphate cycling on glycogen deposition from glucose in fasted-rat hepatocytes using S4048 and CP320626, specific inhibitors of glucose-6-phosphate translocase and glycogen phosphorylase respectively. The effect of amino acids and oleate was also examined. The following observations were made: (1) with glucose alone, net glycogen production was low. Inhibition of glucose-6-phosphate translocase increased intracellular glucose 6-phosphate (3-fold), glycogen accumulation (5-fold) without change in active (dephosphorylated) glycogen synthase (GSa) activity, and lactate production (4-fold). With both glucose 6-phosphate translocase and glycogen phosphorylase inhibited, glycogen deposition increased 8-fold and approached reported in vivo rates of glycogen deposition during the fasted-->fed transition. Addition of a physiological mixture of amino acids in the presence of glucose increased glycogen accumulation (4-fold) through activation of GS and inhibition of glucose-6-phosphatase flux. Addition of oleate with glucose present decreased glycolytic flux and increased the flux through glucose 6-phosphatase with no change in glycogen deposition. With glucose 6-phosphate translocase inhibited by S4048, oleate increased intracellular glucose 6-phosphate (3-fold) and net glycogen production (1.5-fold), without a major change in GSa activity. It is concluded that glucose cycling in hepatocytes prevents the net accumulation of glycogen from glucose. Amino acids activate GS and inhibit flux through glucose-6-phosphatase, while oleate inhibits glycolysis and stimulates glucose-6-phosphatase flux. Variation in glucose 6-phosphate does not always result in activity changes of GSa. Activation of glucose 6-phosphatase flux by fatty acids may contribute to the increased hepatic glucose production as seen in Type 2 diabetes.
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Project description:The effects of a 4-week deficiency in polyunsaturated fatty acids (PUFA) in isolated rat hepatocytes have been investigated for oxidative phosphorylation and fatty acid, dihydroxyacetone (DHA) or glycerol metabolism. Oxygen uptake was significantly increased (by 20%) with or without fatty acid addition (octanoate or oleate) in the PUFA-deficient group compared with controls. The effect persisted after oligomycin addition but not after that of potassium cyanide, leading to the conclusion that, in these intact cells, the mitochondria were uncoupled. The PUFA-deficient group exhibited a significant decrease in the cytosolic ATP/ADP ratio, whereas the mitochondrial ratio was not affected. PUFA deficiency led to a 16% decrease in DHA metabolism owing to a 34% decrease in glycerol kinase activity; the significant decrease in the ATP/ADP ratio was accompanied by an increase in the fractional glycolytic flux. In contrast, glycerol metabolism was significantly enhanced in the PUFA-deficient group. The role of the glycerol 3-phosphate dehydrogenase step in this stimulation was evidenced in hepatocytes perifused with glycerol and octanoate in the presence of increased concentrations of 2,4-dinitrophenol (Dnp): uncoupling with Dnp led to an enhancement of glycerol metabolism, as found in PUFA deficiency, although it was more pronounced than in controls. The matrix/cytosol gradients for redox potential and ATP/ADP ratio were lower in cells from PUFA-deficient rats, suggesting a decreased mitochondrial membrane potential in accordance with the uncoupling effect. Moreover, a doubling of the mitochondrial glycerol 3-phosphate dehydrogenase activity in the PUFA-deficient group compared with controls led us to conclude that the activation of glycerol metabolism is the consequence of two mitochondrial effects: uncoupling and an increase in glycerol 3-phosphate dehydrogenase activity.
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2023-12-19 | PXD045908 | Pride
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