CONICET | Buscador de Institutos y Recursos Humanos

The established defense strategy for cells of different organisms against hypotonic swelling is to promote cellular water efflux via osmosis, thereby leading to a reduction of the excessive cellular volume known as regulatory volume decrease (RVD). In many cell systems the RVD can be modulated by extracellular concentration of different nucleotides, mainly ATP. Thus, in these cells systems challenged by hypotonicity, multiple factors control ATP in the extracellular medium that operate simultaneously to yield a non-linear kinetic of extracellular ATP. Here, a mathematical model was built to account for the kinetic of extracellular ATP (ATPe) and extracellular ADP (ADPe) concentrations from goldfish hepatocytes exposed to hypotonicity. The model was based on previous experimental results on the time course of cell volume, ATPe accumulation, ectoATPase activity and cell viability. The kinetic of ATPe is controlled by a lytic ATP flux, a non-lytic ATP flux and ecto-ATPase activity, whereas ADPe kinetic is governed by a lytic ADP flux and both ecto-ATPase and ecto-ADPase activities. Non-lytic ATPe efflux was included as a diffusion equation modulated by ATPe activation (positive feedback) and ADPe inhibition (negative feedback). The model was able to fit the experimental time evolution of ATPe and simulated the concomitant kinetic of ADPe. According to the model, during the first minute of hypotonicity the concentration of ATPe is mainly governed by both lytic and non-lytic ATP efflux, whilst the ecto-ATPase activity becomes important in the last part of the response. ADPe inhibition of the non-lytic ATP efflux was strong, whereas ATPe activation was minimal. This study demonstrates that ATPe efflux after hypotonic shock would suffer a slight positive modulation by ATP and a strong negative one by ADP.