| The cytosolic concentration of Ca2+ is used as an information carrier in all eukaryotic cells and is also involved in neural information processing in different ways. First Ca2+ is needed for vesicel fusion in the presynapsis and for the activation of the postsynapsis and second neurons are coupled with non eletric excitable cells, astrocytes, which exhibit intra and intercellular Ca2+ waves. Ca2+ signalling has been considered as a deterministic oscillatory system for about two decades by now. In this talk we will show that Ca2+ oscillations are a sequence of random spikes instead. The standard deviation of interspike intervals (ISI) of individual spike trains reaches the same order of magnitude as the average ISI, the standard deviation grows proportional to the average ISI and consecutive ISI are uncorrelated. Decreasing effective diffusion by Ca2+ binding proteins increases the average ISI and the standard deviation in agreement with the idea that individual concentration spikes are caused by random wave nucleation. This role of spatial coupling together with previous observations of wave nucleation processes and theoretical predictions identifies intracellular Ca2+ signalling as stochastic medium. Array enhanced coherence resonance leads to regular Ca2+ oscillations with almost vanishing standard deviation of ISI. |
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