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A Model-Independent Algorithm to Derive Ca²⁺ Fluxes Underlying Local Cytosolic Ca²⁺ Transients

Alejandra C. Ventura ^*, Luciana Bruno ^*, Angelo Demuro , Ian Parker  and Silvina Ponce Dawson ^* 

^* Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina; Department of Neurobiology and Behavior, University of California, Irvine, California; and T10-Theoretical Biology and Biophysics Group, Los Alamos National Laboratory, Los Alamos, New Mexico

Correspondence: Address reprint requests to Silvina M. Ponce Dawson, PhD, Tel.: 54-11-4576-3353; E-mail: silvina{at}df.uba.ar.

Local intracellular Ca²⁺ signals result from Ca²⁺ flux into the cytosol through individual channels or clusters of channels. To gain a mechanistic understanding of these events we need to know the magnitude and spatial distribution of the underlying Ca²⁺ flux. However, this is difficult to infer from fluorescence Ca²⁺ images because the distribution of Ca²⁺-bound dye is affected by poorly characterized processes including diffusion of Ca²⁺ ions, their binding to mobile and immobile buffers, and sequestration by Ca²⁺ pumps. Several methods have previously been proposed to derive Ca²⁺ flux from fluorescence images, but all require explicit knowledge or assumptions regarding these processes. We now present a novel algorithm that requires few assumptions and is largely model-independent. By testing the algorithm with both numerically generated image data and experimental images of sparklets resulting from Ca²⁺ flux through individual voltage-gated channels, we show that it satisfactorily reconstructs the magnitude and time course of the underlying Ca²⁺ currents.

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