Heat stress-activated, calcium-dependent nitric oxide synthase in sponges

The presence of Ca2+-dependent, heat-stress-activated nitric oxide synthase (NOS) activity in peculiarly shaped, fusiform, and dendritic sponge cells is described for the first time. The NOS activity was evidenced evaluating the conversion of radioactive citrulline from [C-14]arginine in intact cell s from two different species that are phylogenetically unrelated in the cla ss of Demospongiae: Axinella polypoides and Petrosia ficiformis. The produc tion of nitrogen monoxide (NO) was confirmed by electron paramagnetic reson ance analysis, and the histochemistry technique of NADPH diaphorase showed a specific localization of NOS activity in a particular network of dendriti c cells in the sponge parenchyma. Sponges are the most primitive metazoan g roup; their evolution dates back 600 million years. The presence of environ mental stress-activated NOS activity in these organisms may prove to be the most ancient NO-dependent signaling network in the animal kingdom. (C) 200 1 Academic Press.