A new model for ATP release from hypotonically exposed hepatocytes from goldfish

PAFUNDO DIEGO; CHARA OSVALDO; SCHWARZBAUM PABLO JULIO

Montevideo

Congreso; 5th Southern Cone Biophysics Congress. 6th International Conference of Biological Physics.; 2007

IUPAP - SAB

Nearly all cell types possess mechanisms that enable the release of ATP in response to an hypotonic challenge. Following cell swelling,extracellular ATP (ATPe) activate specific P receptors that allow the cell to downregulate its volume towards isotonic values. This workaimed at studying the factors governing the kinetics of ATPe of hypotonically exposed goldfish hepatocytes. Under hypotonicity theconcentration of ATPe is mainly governed by lytic and non-lytic release of the nucleotide, hydrolysis of ATP by ecto-ATPase activity at thecell surface and ATP diffusion within the extracellular compartment. We found that goldfish hepatocytes release ATP after hypotonic shock.The time course of ATPe is non-monotonic showing a maximum at 725±165 nM (106 cells)-1. In order to simulate the kinetics of ATPe wedeveloped a one dimensional mathematical model with three compartments: the intracellular (i), an extracellular near to the cells membrane(e1), and one representing the bulk extracellular medium (e2). ATPe is controlled by: 1) non-lytic release of ATP (JNL), 2) lytic ATP release,3) Ecto-ATPase activity in e1, 4) ATP diffusion between e1 and e2. JNL was described as a function JR multiplied by a function Faccounting for a positive feedback mechanism. Four different JR were tested; i) constant JR, ii) step function (JR is zero until it becomesactivated and remains constant thereafter); iii) impulse function (JR has the form of a rectangular pulse that can be triggered and shut off atvariable times); iV) a log-normal function which includes a non-linear fast increase to a maximum, followed by a relatively slowly non-lineardecrease. Use of JR functions i-iv did not allow the model to provide a good fit to experimental data. However, using the log-normal functionwe simulated the kinetics of ATPe with reasonable accuracy. The predicted JNL showed a 1.93 10-18 mol sec-1 peak after 2 sec. The modelwas also used to quantify the relative importance of processes 1-4 in determining the kinetics of ATPe.