Modeling stochastic Ca2+ release from a cluster of IP3-sensitive receptors

We focused our attention on Ca2+ release from the endoplasmic reticulum through a cluster of inositol(1,4,5)-trisphosphate (IP3) receptor channels. The random opening and closing of these receptors introduce stochastic effects that have been observed experimentally. Here, we present a stochastic version of Othmer-Tang model (OTM) for IP3 receptor clusters. We address the average behavior of the channels in response to IP3 stimuli. In our stochastic simulation we found that the fraction of open channels versus [IP3] follows a Hill curve, whose associate Hill coefficient increases when intracellular Ca2+ level increase. This finding suggests that feedback from cytosolic Ca2+ plays a key role in the channel response to IP3. We also study several aspects of the stochastic properties of Ca2+ release and we compare with experimental observations.