  It is shown, by means of numerical simulations, that intercellular spiral
waves of calcium can be initiated in a network of coupled cells as a result of
a de-synchronization between Ca2+ oscillations in two domains. No artificial
heterogeneities need to be imposed to the system for spontaneous formation of
spiral waves. The de-synchronization occurs near the interface of the
stimulated region (which acts as a pacemaker) and propagates over the entire
network. We also find the outcome of the collision of two spiral waves.
