CONICET | Buscador de Institutos y Recursos Humanos

Many natural phenomena display self-organized criticality(SOC), (Baketal.,1987). This refers to spatially extended systems for which patterns of activity characterized by different lengthscales can occur with a probability densiy that follows a power law with pattern size. Differently from power laws at phase transitions, systems displaying SOC do not need the tuning of an external parameter. Here we analyze intracellular calcium(Ca2+)signals, a key component of the signaling toolkit of almost any cell type. Ca2+signals can either be spatially restricted (local)or propagate throughout the cell(global). Different models have suggested that the transition from local to global signals is similar to that of directed percolation. Directed percolation has been associated,inturn,to the appearance of SOC. In this paper we discuss these issues within the framework of simple models of Ca2+signal propagation.We also analyze the size distribution of local signals(puffs)observed in immature XenopusLaevisoocytes. The puff amplitude distribution obtained from observed local signals is not Gaussian with a noticeable fraction of large size events.The experimental distribution of puff are as in the spatio-temporal record of the image has along tail that is approximately log-normal. The distribution canal so be fitted with a power law relation ship albeit with a smaller goodness of fit. The powerlaw behavior is encountered within a simple model that includes some coupling among individual signals for a wide range of parameter values.Ananalysis of the model showsthataglobalelevationoftheCa2+concentrationplaysamajorroleindeterminingwhetherthepuffsizedistributionislong-tailedornot.ThissuggeststhatCa2+-clearingfromthecytosoliskeytodeterminewhetherIP-mediatedCa23+signalscandisplayaSOC-likebehaviorornot.