It has become evident in the last two or three years that random opening and closing of release channels has a major impact on the formation of temporal and spatial structures in intracellular calcium dynamics. That is based to a large extend on the spatially discrete arrangement of channels into clusters and the large concentration gradients occuring during release. I'll present results of simulations of single release events as well as large scale simulations of stochastic models. Implications for future modeling as well as experiments are discussed.