Antagonistic regulation of the glucose/glucose 6-phosphate cycle by insulin and glucagon in cultured hepatocytes
- 15 August 1986
- journal article
- research article
- Published by Portland Press Ltd. in Biochemical Journal
- Vol. 238 (1), 185-191
- https://doi.org/10.1042/bj2380185
Abstract
Flux through the glucose/glucose 6-phosphate cycle in cultured hepatocytes was measured with radiochemical techniques. Utilization of [2-3H]glucose was taken as a measure of glucokinase flux. Liberation of [14C]glucose from [U-14C]glycogen and from [U-14C]lactate, as well as the difference between the utilization of [2-3H]glucose and of [U-14C]glucose, were taken as measures of glucose-6-phosphatase flux. (1) At constant 5 mM-glucose and 2 mM-lactate concentrations insulin increased glucokinase flux by 35%; it decreased glucose-6-phosphatase flux from glycogen by 50%, from lactate by 15% and reverse flux from external glucose by 65%, i.e. overall by 40%. (2) Glucagon had essentially no effect on glucokinase flux; it enhanced glucose-6-phosphatase flux from glycogen by 700%, from lactate by 45% and reverse flux from external glucose by 20%, i.e. overall by 110%. (3) At constant glucose concentrations cellular glucose 6-phosphate concentrations were essentially not altered by insulin, but were increased by glucagon by 230%. In conclusion, under basic conditions without added hormones the glucose/glucose 6-phosphate cycle showed only a minor net glucose uptake, of 0.03 .mu.mol/min per g of hepatocytes; this flux was increased by insulin to a net glucose uptake of 0.21 .mu.mol/min per g and reversed by glucagon to a net glucose release of 0.22 .mu.mol/min per g. Since the glucose-6-phosphate concentrations after hormone treatment did not correlate with the glucose-6-phosphatase flux, it is suggested that the hormones influenced the enzyme activity directly.This publication has 40 references indexed in Scilit:
- Incorporation of glucose into glycogen in primary cultures of rat hepatocytesCanadian Journal of Biochemistry and Cell Biology, 1985
- A putative second messenger of insulin action regulates hepatic microsomal glucose-6-phosphataseBiochemical and Biophysical Research Communications, 1984
- Short‐term modulation of glycogen metabolism, glycolysis and gluconeogenesis by physiological oxygen concentrations in hepatocyte culturesEuropean Journal of Biochemistry, 1983
- A critical evaluation of the possible modulation of hepatic microsomal glucose-6-phosphatase activity by protein phosphorylationBiochemical and Biophysical Research Communications, 1982
- Evidence for protein phosphorylation as a regulatory mechanism for hepatic microsomal glucose 6 phosphataseBiochemical and Biophysical Research Communications, 1981
- Hormone-induced effects on the rat liver microsomal glucose-6-phosphatase system in vitroBiochemical and Biophysical Research Communications, 1981
- The Role of Futile Cycles in the Regulation of Carbohydrate Metabolism in the LiverPublished by Wiley ,1981
- Heterogeneous reciprocal localization of fructose‐1,6‐bis‐phosphatase and of glucokinase in microdissected periportal and perivenous rat liver tissueFEBS Letters, 1977
- Futile cycles in isolated perfused rat liver and in isolated rat liver parenchymal cellsBiochemical and Biophysical Research Communications, 1975
- Isotopic evidence for futile cycles in liver cellsBiochemical and Biophysical Research Communications, 1973