Analysis of cellular exposure to peroxynitrite in suspension cultures

A mathematical model was developed to predict the intracellular concentrations of NO, O(2)(-), and peroxynitrite in suspension cell cultures exposed to NO and/or peroxynitrite. Oxygen and CO(2) were also considered. Steady state concentrations were computed as a function of radial position within an idealized spherical cell, with a distinction being made between cytosolic and mitochondrial values. Spatial variations in the intracellular concentrations of O(2), CO(2), and NO were found to be negligible. The extremely low membrane permeabilities for O(2)(-) (estimated from lipid bilayer data) caused O(2)(-) to be consumed in the compartment in which it was generated (mitochondria or cytosol) and resulted in concentrations that depended on the generation rate and the concentrations of superoxide dismutase and NO in the individual compartments. Special attention was paid to the origins of intracellular peroxynitrite. Potential sources of peroxynitrite include intracellular generation in mitochondria and cytosol and (depending on the type of experiment) diffusion of extracellular peroxynitrite into the cell. The relative importance of extracellular and intracellular sources was estimated for a wide variety of conditions. The calculated mitochondrial concentrations were generally 5-10 times higher than the cytosolic values, and it was found that mitochondria may act either as sources or sinks for cytosolic peroxynitrite, depending on the experimental conditions. For the baseline conditions, including an NO concentration of 1 microM and no peroxynitrite in the medium, the cytosolic peroxynitrite concentration was estimated as approximately 2 nM. The extracellular peroxynitrite concentration required to double the cytosolic level was approximately 25 nM, and an extracellular concentration of approximately 100 nM was needed to effect a 5-fold increase. For extracellular concentrations smaller than 25 nM, intracellular generation predominated.