Stimulation and inhibition of nitric oxide production in macrophages and neural cells as observed by spin trapping

We have combined electron paramagnetic resonance (EPR) and spin trapping techniques to measure nitric oxide (NO) production by activated macrophages and neural cells in vitro. Macrophages stimulated by bacterial lipopolysaccharide (LPS), gamma interferon (IFNγ), or both, produced NO. Differentiated and undifferentiated neural cells activated by KCl and CaCl₂. N-methyl-D-aspartate (NMDA), and IFNγ were shown to produce NO as well. The mechanism of activation in neural cells could be either by channels or receptors. Maximum NO production in macrophages was achieved when stimulated by a combination of LPS and IFNγ administered sequentially or concurrently, IFNγ was the most effective stimulant for neural cells. The in vitro production of NO by all these cells was inhibited by N(G)-monomethyl L- arginine (L-NMMA) in a dose dependent manner. Complete inhibition of NO production occurred when cells were grown in L-arginine free medium, indicating that L-arginine was essential for NO production. We also concluded from our study that NO production in macrophages was in greater amounts and more long lasting in duration than that observed in the neural cells.