Detection of Low Levels of Nitric Oxide Using an Electrochemical Sensor

Nitric oxide produced from nitric oxide synthases mediates various physiological and pathological events in biological systems. However, quantitative assessment of nitric oxide from biological sources remains a difficult task. Here we describe a procedure for the quantification of low levels of nitric oxide using a nitric oxide – selective electrochemical sensor. Nitric oxide is oxidized to nitrite and/or nitrate and accumulated in the aqueous media. First, nitrate in biological fluids or culture media is converted to nitrite by an enzymatic method. Nitrite is then chemically converted to equimolar NO in an acidic iodide bath, where nitric oxide is detected by the sensor. Using this method, the present study demonstrates siRNA -mediated suppression of nitric oxide synthase 3 leading to a significant decline of basal nitric oxide production in human umbilical vein endothelial cells. Basal nitric oxide production from HUVECs is also shown to be inhibited by N ^G -nitro-l -arginine methyl ester but not by N ^G -nitro-d -arginine methyl ester (D-NAME) . The analytical method presented here provides a sensitive and convenient tool for measuring basal and stimulated nitric oxide production from biological sources.