title: Is the real in vivo nitric oxide concentration pico or nano molar? Influence of electrode size on unstirred layers and NO consumption.
abstract: OBJECTIVE
  There is a debate if the [NO] required to influence vascular smooth muscle is below 50 nM or much higher. Electrodes with 30 μm and larger diameter report [NO] below 50 nM, whereas those with diameters of <10-12 μm 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 μm × 2 mm carbon fiber, and single 7 μm diameter carbon fiber within open tip microelectrode, and exposed 7 μm carbon fiber of ~15 μm to 2 mm length.
  
  
  RESULTS
  All electrodes demonstrated linear calibrations with sufficient stirring. As stirring slowed, 30 μm and 2 mm electrodes reported much lower [NO] due to unstirred layers and high NO consumption. The three 7 μm microelectrodes had minor stirring issues. With limited stirring with NO present, 7 μm open tip microelectrodes advanced toward 30 μm and 2 mm electrodes experienced dramatically decreased current within 10-50 μm of the larger electrodes due to high NO consumption. None of the 7 μm 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.
authors.affiliation: Department of Cellular and Integrative Physiology, Indiana University Medical School, Indianapolis, Indiana 46140, USA. gbohlen@iupui.edu
authors.forename: H Glenn
authors.initials: HG
authors.lastname: Bohlen
mesh_terms: D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000502:physiology; D008297:Male; D008832:Microchemistry / Q000295:instrumentation / Q000379:methods; D008839:Microelectrodes; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D009569:Nitric Oxide / Q000032:analysis* / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology
chemical_list: D009569:Nitric Oxide