Nitric oxide generation by hemocytes of the mussel Mytilus galloprovincialis

The phagocytic activity of Mytilus galloprovincialis hemocytes is thought t o be associated with NADPH-oxidase activity of the plasma membrane, thus pr oducing superoxide anions. Few studies, however, have been devoted to nitri c oxide release by these haemocytes. We investigated NO generation in M. ga lloprovincialis in order to understand its role in the defensive mechanisms of these organisms. The presence of NO-synthase-like enzymatic activity in protein homogenates from M. galloprovincialis hemocytes was revealed by th e conversion of radiolabelled L-arginine to L-citrulline. We observed parti al inhibition of the luminol-dependent chemiluminescence of stimulated M. g alloprovincialis hemocytes by both NO-synthase inhibitors and superoxide di smutase, indicating that peroxynitrite (which results from the reaction bet ween nitric oxide and superoxide anions) partially mediated this chemilumin escence. Furthermore, we confirmed the production of nitric oxide by M. gal loprovincialis by highlighting the nitric oxide-synthase-dependence of the nitrate and nitrite production of stimulated hemocytes. (C) 2001 Academic P ress.