NOS1 and neuroblastoma: Our study further demonstrates that nNOS in both, A673 neuroepithelioma and TGW-nu-I neuroblastoma cells can fast and efficiently be nourished by extracellular arginine (arginine pool I that is freely exchangeable between the intra- and extracellular space): Under all experimental conditions (e.g. after arginine depletion with extracellular lysine and inhibition of protein breakdown), NO synthesis fully recovered within 4 min upon addition of extracellular arginine.