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Stochastic binding of Ca 2+ ions in the dyadic cleft; continuous vs random walk description of diffusion
Author(s) -
Hake Johan,
Lines Glenn Terje
Publication year - 2007
Publication title -
pamm
Language(s) - English
Resource type - Journals
ISSN - 1617-7061
DOI - 10.1002/pamm.200700621
Subject(s) - random walk , diffusion , statistical physics , stochastic modelling , stochastic process , stochastic simulation , mathematics , physics , chemistry , statistics , thermodynamics
Ca 2+ signaling in the dyadic cleft in ventricular myocytes is fundamentally discrete and stochastic. In this paper we study the stochastic binding of single Ca 2+ ions to receptors in the cleft using two different models of diffusion; a stochastic and discrete Random walk (RW) model, and a deterministic continuous model. We investigate if the latter model, together with a stochastic receptor model, can reproduce binding events registered in fully stochastic RW simulations. By evaluating the continuous model goodness‐of‐fit, we present evidences that it can. The large fluctuations in binding rate observed at the time level of single time steps are integrated and smoothed at the larger time scale of binding events, explaining the continuous model goodness‐of‐fit. With this we demonstrate that the stochasticity and discreteness of the Ca 2+ signaling in the dyadic cleft, determined by single binding events, can be described with a deterministic model of Ca 2+ diffusion together with a stochastic model of the binding events. Time consuming RW simulations can thus be avoided. We also present a new analytical model of bi‐molecular binding probabilities that is used in the RW simulations, and in the statistical analysis. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)