Development of the in vivo monitoring system of nitric oxide using a micro electrode.

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Following the electrochemical analysis of the oxidation reaction mechanism of nitric oxide(NO) on the electrode surface and examination of the materials for the electrode itself and its surface coating, we developed three types of electrode for the detection of trace amount of NO in biological tissues ; (1) a glassy carbon electrode covered with Nafion film containing iron porphyrins, (2) a pencil lead elecrode covered with Nafion, alpha-cyclodextrin and PDDA (cation polymer), and(3) a carbon fiber electrode covered with Nafion and PDDA.The interference in the detection of NO by several redox substances existed in tissues such as NO_2, ascorbic acid and catecholamines, could be effectively abolished by coating the electrode with Nafion, PDDA and alpha-cyclodextrin. The sensitivity for No was increased by adding iron porphyrins in Nafion film due to its catalytic properties. Thus, the electrodes could detect 10^9MNO in solution.Using the glassy carbon electrode coated with Nafion film containing iron porphyrins, we could detect NO release from the isolated rat thoracic aorta stimulated by acetyl choline, and the concentration of NO was estimated about 100nM.The specificity was confirmed by the evidence that the amperometric signal was diminished by removal of the endothel from the blood vessel or addition of L-NAME,a NO synthase inhibitor. Furthermore, the electrode could detect NO release from the cultured bovine endothelial cells. We are trying in vivo application of the detection system using the carbon fiber electrode, and the result is promising.