In general, most signal molecules work via conformational matching with a complementary receptor. Nitric oxide appears to work via modulating its concentration in a particular microenvironment. In this regard, the presence of nitric oxide synthase (NOS) isoforms is critical to this modulation. As the name implies, constitutive NOS produces basal levels of nitric oxide that can be enhanced when called for by physical means, i.e, mechanotransduction in blood vessels, and/or classical signaling molecules coupled to constitutive NOS activation, i.e, acetylcholine. If higher and/or sustained levels of nitric oxide are called for, as in a strong proinflammatory response, inducible NOS, after a latent period, emerges. In all, for such a small, simple gas molecule,its actions are diverse and complex. Its relevance in biological systems is further highlighted by finding it performing the same functions in invertebrates, implying that it has a long evolutionary history and was necessary in this evolvement as well.
This text focuses attention on many of the above mentioned phenomena associated with nitric oxide signaling. It further focuses attention on the basal level of nitric oxide and its implications. Nitric oxide levels measured in real time, via nitric oxide probes, have revealed that basal levels of this gas are present and controlling physiological states of cellular activation. This, in itself, opens another key avenue of nitric oxide research with clinical relevance since it expands our understanding of the basic functioning of different organ systems. In this regard, we are still just beginning to comprehend the significance of nitric oxide in living systems, as well as in understanding various pathologies.
