A theoretical study of effects of cytosolic Ca2+ oscillations on activation of glycogen phosphorylase Original Research Article

Taking into account the Ca2+-stimulated degradation of inositol 1,4,5-trisphosphate (IP3) by a 3-kinase, we have theoretically explored the effects of both simple and complex Ca2+ oscillations on the regulation of a phosphorylation–dephosphorylation cycle process involved in glycogen degradation by glycogen phosphorylase a-form, respectively. For the case of simple Ca2+ oscillations, the roles of cytosolic Ca2+ oscillations in the regulation of active phosphorylase depend upon the maximum rate of IP3 degradation by the 3-kinase, VM5. In particular, the smaller the values of VM5 are, the lower the effective Ca2+ threshold for the activation of glycogen phosphorylase will be. For the case of complex Ca2+ oscillations, the average level of fraction of active phosphorylase is nearly independent from the level of stimulation increasing in the bursting oscillatory domain. Both simple and complex Ca2+ oscillations can contribute to increase the efficiency and specificity of cellular signalling, and some theoretical results of activation of glycogen phosphorylase regulated by Ca2+ oscillations are close to the experimental results for gene expression in lymphocytes.