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lüll Is the real in vivo nitric oxide concentration pico or nano molar? Influence of electrode size on unstirred layers and NO consumption Bohlen HGMicrocirculation 2013[Jan]; 20 (1): 30-41OBJECTIVE: There is a debate if the [NO] required to influence vascular smooth muscle is below 50 nM or much higher. Electrodes with 30 mum and larger diameter report [NO] below 50 nM, whereas those with diameters of <10-12 mum report hundreds of nM. This study examined how size of electrodes influenced [NO] measurement due to NO consumption and unstirred layer issues. METHODS: Electrodes were 2 mm disk, 30 mum x 2 mm carbon fiber, and single 7 mum diameter carbon fiber within open tip microelectrode, and exposed 7 mum carbon fiber of ~15 mum to 2 mm length. RESULTS: All electrodes demonstrated linear calibrations with sufficient stirring. As stirring slowed, 30 mum and 2 mm electrodes reported much lower [NO] due to unstirred layers and high NO consumption. The three 7 mum microelectrodes had minor stirring issues. With limited stirring with NO present, 7 mum open tip microelectrodes advanced toward 30 mum and 2 mm electrodes experienced dramatically decreased current within 10-50 mum of the larger electrodes due to high NO consumption. None of the 7 mum microelectrodes interacted. CONCLUSIONS: The data indicate large electrodes underestimate [NO] due to excessive NO consumption under conditions where unstirred layers are unavoidable and true microelectrodes are required for valid measurements.|*Microelectrodes[MESH]|Animals[MESH]|Arterioles/drug effects/physiology[MESH]|Male[MESH]|Microchemistry/instrumentation/methods[MESH]|Muscle Relaxation/drug effects/physiology[MESH]|Muscle, Smooth, Vascular/*metabolism[MESH]|Nitric Oxide/*analysis/*metabolism/pharmacology[MESH]|Rats[MESH]|Vasodilation/drug effects/physiology[MESH] |