Mathematical modeling of ATP release in Goldfish hepatocytes

PAFUNDO DIEGO; CHARA OSVALDO

Rosario, Argentina

Congreso; Runíón Anual de la SAB; 2006

Sociedad Argentina de Biofísica (SAB)

Mathematical modeling of ATP release in Goldfish hepatocytes under hypotonic shock Diego Pafundo" and Osvaldo Charabi° "IQUIFIB. Facultad cfe Farmacia y Bioquimica, School of Pharmacy and Biochemistry, University of Buenos Aires, Buenos Aires, Argentina. "IFLYSIB (CONICET, UNLP,CIC), La Plata, Provincia de Buenos Aires, Argentina.'Department of Physiology and Biophysics, School of Medicine, University of Buenos Aires, Buenos Aires, Argentina. e-mail: pafundo@qb.ffyb.iiba.ar In numerous cell types hypotonic shock induces an increase in cell volume followed by ATP release to the extracellular space. Once in the extracellular medium, ATP can trigger signaling pathways and also be substrate of several extracellular enzymes. However, the release mechanism for ATP from cells remains enigmatic. Goldfish (Carassius auratus) hepatocytes release ATP under hypotonic shock [1]. The time course of extracellular ATP [ATP]e is non monotonic showing a maximum at 725 +165 nM (106 cells)1. The ATP releasing pathway and its particular kinetic remain yet unclear. It's known that: 1) dead cells in hypotonic shock (up to 96.9%) could be an [ATP]e increasing source by membrane integrity loss, 2) Ecto-ATPase activity under experimental conditions can completely hydrolyze ATP to adenosine [1, 2], 3) [ATP]e do not permeate into the cells but intracellular ATP diffuses to the extracellular medium [1, 2]. In order to analyze the contribution of the above, we developed a one dimensional mathematical model with three compartments: the intracellular (i), an extracellular near to the cells membrane (e1), and another one representing the bulk extracellular medium (e2). Each compartment is described by the corresponding state variable [ATP]. In the model, the [ATP]e is controlled by: 1) ATP contribution from dead cells, 2) Ecto-ATPase activity in e1, 3) ATP Diffusion from e1 to e2 compartments and 4) ATP releasing from cells by hypotonic shock. The contribution 1) is modeled loading mortality data from experimental conditions, assuming complete ATP loosing. 2) is simulated with an hyperbolic dependence on [ATP]6, which provided the best fit to the experimental data. 3) is emulated with a diffusion equation. 4) is modeled with a function J describing ATP release from cells during hypotonic shock. The model is able to explain the relative importance of each ATP contribution showing that loss of cell viability do not explain [ATP]e, Ecto-ATPase activity and ATP diffusion determine the non-monotonic behavior of the time course of [ATP]e. Interestingly, the simulations show that d J/dt can not be zero nor a constant. References: [1] Pafundo D. E. et al., manuscript in preparation. [2] Schwarzbaum P. J. et al., Am. J. Physiol. 274: 1031-1038, 1998. Acknowledgments: To Dr. P. J. Schwarzbaum