Localization of inducible nitric oxide synthase to mast cells during ischemia/reperfusion injury of skeletal muscle

Nitric oxide contributes to tissue necrosis after ischemia-reperfusion (IR) . A biochemical and immunohistochemical study was made of the amounts and l ocalization of both Ca++-independent nitric oxide synthase (NOS) II and Ca+-dependent (NOS I and NOS III) in rat skeletal muscle after ischemia and 0 .5, 2, 8, 16, and 24 hours reperfusion. NOS II was not detectable in contro l muscle or during ischemia, was first detected after 2 hours reperfusion, increased further by 8 hours, and remained elevated at 24 hours. Both NOS I I and nitrotyrosine, a marker of peroxynitrite formation, were localized ex clusively to mast cells except after 24 hours reperfusion when some macroph ages and neutrophils also showed positive immunoreactivity. Mast cells unde rwent extensive degranulation during reperfusion. NOS I was not detected in injured or control muscle. The level of NOS III, which was localized to th e endothelium of blood vessels of all sizes in control muscle, decreased pr ogressively during ischemia and reperfusion to each undetectable levels aft er 16 hours reperfusion. These findings indicate that most of the nitric ox ide formed during IR injury is generated by NOS II located almost exclusive ly in mast cells.