Nitric oxide delivery system for biological media

Developing an understanding of how chronically elevated levels of nitric oxide at sites of inflammation or infection can lead to cancer and other diseases requires ways to expose cells and biomolecules to controlled concentrations of NO for hours to days. To achieve this, a small (65 ml) stirred reactor was fabricated that included a flat, porous poly(tetrafluoroethylene) membrane and a loop of poly(dimethylsiloxane) tubing for NO and O2 delivery, respectively. It was equipped with probes for continuous monitoring of NO and O2 concentrations. Transport through the membrane and tubing was characterized using separate O2 depletion experiments. In experiments using only a 10% NO mixture and a buffer that was initially air-equilibrated, constant rates of accumulation were observed for NO2− (53 ± 2 μM/h; n = 8), the end product of NO oxidation, as expected. Simultaneous delivery of NO and O2 yielded steady NO concentrations of 0.7-2.3 μM, depending on the tubing length and gas compositions. A model was developed that allows the steady NO and O2 concentrations and the duration of the transients to be predicted to within a few percent. This system should be useful for exposing cells and biomolecules to concentrations of NO that mimic those in vivo.