Some new elements are introduced into a mathematical model of intracellular calcium oscillations,which make it particularly suitable for the study of bifurcation.In addition to generating regular oscillations,such a modified model can be used to reproduce the burst discharges similar to those recorded in experiments and to describe two new types of oscillatory phenomena.By means of a fast/slow dynamical analysis,we explore the bifurcation and transition mechanisms associated with two types of bursters due to changes in the interaction of two slow variables with different timescales.