In rat hepatocytes subjected to a fructose load, ATP content decreased from 3.8 to 2.6 μmol/g of cells. Under these conditions, the intracellular free Mg2+ ion concentration, as measured with mag-fura 2, increased from 0.25 to 0.43 μmol/g of cells and 0.35 μmol of Mg2+ ions were released per g of cells in the extracellular medium. Therefore the increase in the intracellular free Mg2+ ion concentration was less than expected from the decrease in ATP, indicating that approx. 80% of the Mg2+ ions released from MgATP2- were buffered inside the cells. When this buffer capacity was challenged with an extra Mg2+ ion load by blocking the fructose-induced Mg2+ efflux, again approx. 80% of the extra Mg2+ ion load was buffered. The remaining 20% appearing as free Mg2+ ions in fructose-treated hepatocytes could act as second messenger for enzymes having a Km for Mg2+ in the millimolar range. Fructose activated glycogen synthase and glycogen phosphorylase, although both the time course and the dose-dependence of activation were different. This was reflected in a stimulation of glycogen synthesis with concentrations of fructose below 5 mM. Indeed, activation of glycogen synthase reached a maximum at 30 min of incubation and was observed with small (5 mM or less) concentrations of fructose, whereas the activation of glycogen phosphorylase was almost immediate (within 5 min) and maximal with large doses of fructose. The fructose-induced activation of glycogen phosphorylase, but not that of glycogen synthase, could be related to an increase in free Mg2+ ion concentration.
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September 1997
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Research Article|
September 15 1997
Fructose-induced increase in intracellular free Mg2+ ion concentration in rat hepatocytes: relation with the enzymes of glycogen metabolism
Vinciane GAUSSIN;
Vinciane GAUSSIN
*Hormone and Metabolic Research Unit, International Institute of Cellular and Molecular Pathology, ICP-UCL 7529, Avenue Hippocrate, 75, B-1200 Brussels, Belgium
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Philippe GAILLY;
Philippe GAILLY
†Department of Physiology, Louvain University Medical School, UCL 5540, Avenue Hippocrate 55, B-1200 Brussels, Belgium
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Jean-Marie GILLIS;
Jean-Marie GILLIS
†Department of Physiology, Louvain University Medical School, UCL 5540, Avenue Hippocrate 55, B-1200 Brussels, Belgium
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Publisher: Portland Press Ltd
Received:
December 20 1996
Revision Received:
May 12 1997
Accepted:
May 22 1997
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London © 1997
1997
Biochem J (1997) 326 (3): 823–827.
Article history
Received:
December 20 1996
Revision Received:
May 12 1997
Accepted:
May 22 1997
Citation
Vinciane GAUSSIN, Philippe GAILLY, Jean-Marie GILLIS, Louis HUE; Fructose-induced increase in intracellular free Mg2+ ion concentration in rat hepatocytes: relation with the enzymes of glycogen metabolism. Biochem J 15 September 1997; 326 (3): 823–827. doi: https://doi.org/10.1042/bj3260823
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