Release of NO from Donor Compounds: A Mathematical Model for Calculation of NO Concentrations in the Presence of Oxygen

For studies on the biological role of nitric oxide (NO), especially long-term effects of NO on transcriptional or translational regulation of protein expression, it is desired to expose cells to a well-defined NO concentration over a certain period of time. Application of NO gas or NO solutions does not meet this goal, as it gives rise to relatively high initial-NO concentrations followed by a rapid decline owing to autoxidation. This problem can be avoided using NO-donor compounds, which should be stable in solutions of high or low pH and decompose in a first-order reaction to release stoichiometric amounts of NO after dilution in physiological buffers. Though decomposition of most of the currently available NO donors is not that simple, nucleophilic complexes of NO with amines (NONOates) appear to meet these criteria and release NO in a first-order reaction at physiological pH (1 ). However, owing to the complex third-order kinetics of NO autoxidation, i.e., the fact that the rate of NO autoxidation increases with increasing concentrations of NO (2 ), it is difficult to predict the actual NO concentration at a given time point even in this ideal situation.