Table 1.

Isoforms of nitric oxide synthases

	eNOS	iNOS	nNOS
Alias	endothelial NOS, NOS I	inducible NOS, NOS II	neuronal NOS, NOS III
Function	Regulates vascular tissue, blood pressure, inhibits platelet aggregation and leukocyte adhesion	Response to stress and inflammation, involved in host defense and tissue destruction	Involved in neurotransmission, modulates response to pain and neuronal sensitization
Gene expression	Constitutively expressed	Induced in response to Immunostimulatory cytokines or bacterial pathogens	Constitutively expressed
Dependency on Calcium	Calcium- calmodulin dependent	Calcium- calmodulin independent	Calcium- calmodulin dependent
NO production	Small amount (pico to nanomolar)	Large sustained amount of NO (nano to micromolar)	Small amount (pico to nanomolar)
Signal for discontinuation of NO production	Self-limited	NOS degradation	Self-limited
Expression/localization	Endothelium	Chondrocyte, synoviocytes, hepatocyte, macrophages, other	Brain