title: Signalling by O2-. and NO.: how far can either radical, or any specific reaction product, transmit a message under in vivo conditions?
abstract: With regard to the stability of the NO. radical as a chemical entity, it is without doubt able to serve as an intra- as well as an intercellular messenger. The radical O2-., in contrast, does not seem to be suited to far-range signalling in the vascular system. Its short chemical half-life, which is limited by the presence of various reactive blood constituents to below 50 ms, results in a free diffusion path length of less than 40 microns, i.e. only the distance between just a few cells. While accelerated 'downstream' transport by arterial blood may help to extend the action sphere, there is no possibility for O2-. to serve as a signal in an upstream direction. The estimates presented, however, do not invalidate arguments for a possible role of superoxide anions in intra- or pericellular signalling phenomena. Cross-talk between NO.- and O2-.-dependent signal routes, e.g. by peroxynitrite formation, is unlikely to be a relevant process under the conditions which prevail in the vascular system.
authors.affiliation: Institut für Strahlenbiologie, GSF Forschungszentrum für Umwelt und Gesundheit, Neuherberg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Saran
authors.forename: W
authors.initials: W
authors.lastname: Bors
mesh_terms: D001775:Blood Circulation; D005609:Free Radicals / Q000097:blood; D008954:Models, Biological; D009589:Nitrogen Oxides / Q000097:blood; D015290:Second Messenger Systems / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D013481:Superoxides / Q000097:blood
chemical_list: D005609:Free Radicals; D009589:Nitrogen Oxides; D013481:Superoxides; C039900:nitroxyl