"... While varying extracellular or intracellular Ca2+ concentration assesses the intrinsic biochemical Ca2+ cooperativity of neurotransmitter release, varying the number of open Ca2+ channels using pharmacological channel block or the tail current titration probes the cooperativity between individual Ca2+ channels in triggering exocytosis. ... Here we provide a detailed analysis of the Ca2+ sensitivity measures probed by these experimental protocols, present simple expressions for special cases, and demonstrate the distinction between the Ca2+ current cooperativity, defined by the relationship between exocytosis rate and the whole-terminal Ca2+ current magnitude, and the underlying Ca2+ channel cooperativity, defined as the average number of channels involved in the release of a single vesicle. ... Further, we use three-dimensional computational modeling of buffered Ca2+ diffusion to analyze these distinct Ca2+ cooperativity measures, and demonstrate the role of endogenous Ca2+ buffers on such measures. We show that buffers can either increase or decrease the Ca2+ current cooperativity of exocytosis, depending on their concentration and the single-channel Ca2+ current."
Model Type: Channel/Receptor
Model Concept(s): Calcium dynamics
Simulation Environment: CalC Calcium Calculator (web link to model)
Implementer(s): Matveev, Victor V. [m a t v e e v at n j i t . e d u ]
References:
Matveev V, Bertram R, Sherman A. (2009). Ca2+ current versus Ca2+ channel cooperativity of exocytosis. The Journal of neuroscience : the official journal of the Society for Neuroscience. 29 [PubMed]