Effects of inositol 1,4,5-trisphosphate receptor-mediated intracellular stochastic calcium oscillations on activation of glycogen phosphorylase Original Research Article

In various cell types cytosolic calcium (Ca2+) is an important regulator. The possible role of Ca2+ release from the inositol 1,4,5-trisphosphate (IP3) receptor channel in the regulation of the phosphorylation–dephosphorylation cycle process involved in glycogen degradation by glycogen phosphorylase have theoretically investigated by using the Li–Rinzel model for cytosolic Ca2+ oscillations. For the case of deterministic cytosolic Ca2+ oscillations, there exists an optimal frequency of cytosolic Ca2+ oscillations at which the average fraction of active glycogen phosphorylase reaches a maximum value, and a mutation for the average fraction of active glycogen phosphorylase occurs at the higher bifurcation point of Ca2+ oscillations. For the case of stochastic cytosolic Ca2+ oscillations, the fraction of active phosphorylase is strongly affected by the number of IP3 receptor channels and the level of IP3 concentration. Small number of IP3 receptor channels can potentiate the sensitivity of the activity of glycogen phosphorylase. The average frequency and amplitude of active phosphorylase stochastic oscillations are increased with the level of increasing IP3 stimuli. The various distributions for the amplitude of active glycogen phosphorylase oscillations in parameters plane are discussed.