Practical methods for detection of nitric oxide.

Nitric oxide (NO), which is generated in vivo through conversion of L-arginine to L-citrulline by NO synthase (NOS), mediates many physiological and pathophysiological processes. At least two distinct isoforms of NOS have been identified, constitutive NOS (cNOS) and inducible NOS (iNOS). The cNOS, which is constitutively expressed in endothelial cells and central and peripheral neuronal cells, requires both calcium and calmodulin for its activation. Cells expressing cNOS generally produce small amounts of NO, because of their low levels of cNOS protein. On the other hand, iNOS, which is induced in cells stimulated with endotoxins, produced larger amounts of NO. Because of the short half-life, it is difficult to detect NO in situ directly, especially from cells expressing cNOS. In this review, we discuss practical methods for NO detection, which are useful for the detection of small amounts of NO from cNOS and for the bioimaging of living cells and cultured tissues.