Dynamics of intracellular Ca2+ oscillations in the presence of multisite Ca2+-binding proteins

We study the dynamics of intracellular calcium oscillations in the presence of proteins that bind calcium on multiple sites and that are generally believed to act as passive calcium buffers in cells. These multisite calcium-binding proteins set a sharp threshold for calcium oscillations, and calcium oscillations stop at high concentrations of calcium- binding proteins. However even in these adverse conditions, internal noise, which shows up spontaneously in cells in the process of calcium wave formation, can lead to self- oscillations. This produces oscillatory behaviors strikingly similar to those observed in real cells. In addition, for given intracellular concentrations of both calcium and calcium- binding proteins the regularity of these oscillations changes and reaches a maximum as a function of the noise variance, and we find that the overall system dynamics displays coherence resonance. Thus it turns out that the calcium-binding proteins can have an important and non-trivial regularizing role.