Intra-cluster percolation of calcium signals

GUILLERMO SOLOVEY; SILVINA PONCE DAWSON

Workshop; Latin American Workshop on Nonlinear Phenomena. LAWNP´09; 2009

Calcium signals are involved in a large variety of physiological processes. Their versatility relies on the diversity of spatio-temporal behaviors that the calcium concentration can display. Calcium entry through inositol 1,4,5-trisphosphate receptors (IP3R?s) is a key component of the calcium signaling toolkit. IP3R?s are usually organized in clusters on the membrane of the endoplasmic reticulum and their spatial distribution has important effects on the resulting signal. Recent high resolution observations give accurate estimates of the number of channels that open during localized release events offering a window to study intra-cluster organization. In this talk I will present a simple model with which we interpret the observations in terms of two stochastic effects: IP3 binding and unbinding and Ca2+-mediated inter-channel coupling. Depending on the parameters, one or the other process may be dominating. The transition between both limiting cases, a fingerprint of which can be encountered in the distribution of event sizes, is similar to percolation. By analyzing the distribution it is possible to infer properties of the interactions among channels from statistical information on the emergent behavior of the cluster as a whole.