Talk abstract:

Theoretical Investigation of the Effect of Ca²⁺ Oscillations on the Balance Between Glycogen Synthesis and Degradation in the Liver

Geneviève Dupont
Theoretical Chronobiology Unit
Free University of Brussels CP231
B-1050 Brussels, Belgium
gdupont@ulb.ac.be

Joint work with Erika Baus and Albert Goldbeter.

In many cell types, Ca²⁺ controls specific cellular processes such as contraction, secretion and metabolic pathways. The Ca²⁺ rise induced by external stimulation often consists of a series of transients, whose frequency increases with the dose of agonist (Berridge, 1997). In the liver, such Ca²⁺oscillations can be induced by the hormones vasopressin and phenylephrine as well as by the neurotransmitter noradrenaline (Woods et al., 1986). These three agonists moreover lead to the release of glucose from glycogen in hepatocytes. This effect is known to be mediated by the stimulation of phosphorylase kinase activity by the Ca²⁺/calmodulin complex. The latter kinase indeed induces the transformation of the glycogen phosphorylase into an active form, which degrades glycogen into glucose. By extending a model previously developped to study the switch between glycogen synthesis and degradation in the liver (Cardenas and Goldbeter, 1996), we analyze theoretically the effect of Ca²⁺ oscillations on the fraction of active phosphorylase kinase. We predict that Ca²⁺ oscillations can potentiate glycogen degradation at low stimulation levels.

References

1. Berridge M.J. (1997) Elementary and global aspects of calcium signalling. J. Physiol. 499, 291-306.
2. Woods N., Cuthbertson K. and Cobbold P. (1986) Repetitive transient rises in cytoplasmic free calcium in hormone-stimulated hepatocytes. Nature 319, 600-602.
3. Cardenas M.L. and Goldbeter A. (1996) The glucose-induced switch between glycogen phosphorylase and glycogen synthase in the liver: outlines of a theoretical approach. J. Theor. Biol. 182, 421-426.

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1998-1999 Mathematics in Biology