Fatty acid and amino acid modulation of glucose cycling in isolated rat hepatocytes.
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.
Gustafson
L A
LA
Department of Biochemistry, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Neeft
M
M
Reijngoud
D J
DJ
Kuipers
F
F
Sauerwein
H P
HP
Romijn
J A
JA
Herling
A W
AW
Burger
H J
HJ
Meijer
A J
AJ
D000255:Adenosine Triphosphate / Q000378:metabolism; D000577:Amides / Q000494:pharmacology*; D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D017920:Antiporters; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005215:Fasting; D005941:Glucokinase / Q000378:metabolism; D005943:Gluconeogenesis / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000378:metabolism*; D019298:Glucose-6-Phosphate / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology*; D007211:Indoles / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000166:cytology; D008112:Liver Glycogen / Q000096:biosynthesis*; D008297:Male; D009004:Monosaccharide Transport Proteins; D019301:Oleic Acid / Q000494:pharmacology*; D010763:Phosphorylase b / Q000037:antagonists & inhibitors; D010770:Phosphotransferases / Q000037:antagonists & inhibitors; D011725:Pyridines / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
D000577:Amides; D000596:Amino Acids; D017920:Antiporters; D004791:Enzyme Inhibitors; D007093:Imidazoles; D007211:Indoles; D008112:Liver Glycogen; D009004:Monosaccharide Transport Proteins; D011725:Pyridines; C403582:S 4048; C503533:Slc37a4 protein, rat; C111261:glucose 6-phosphate(transporter); D019301:Oleic Acid; D019298:Glucose-6-Phosphate; D000255:Adenosine Triphosphate; D010763:Phosphorylase b; D010770:Phosphotransferases; D005941:Glucokinase; C412544:CP 320626; D005947:Glucose