Table 2.

NOS isoforms

	Neural (n NOS, type 1)	Inducible (iNOS, type 2)	Endothelial (eNOS, type 3)
Cells first identified in	Neurons	Macrophages	Endothelium
Other cells expressing	Myocytes	Astrocytes	Neurons
	Astrocytes	Microglia
Intracellular localization	Soluble or membrane bound	Soluble or membrane bound	Largely membrane bound
Ca2+ dependency	Activity depends on elevated Ca2+	Activity is independent of elevated Ca2+	Activity depends on elevated Ca2+
Expression	Constitutive inducible under certain circumstances, eg, trauma	Inducible	Constitutive
Amounts of NO released	Small, pulses	Large, continuous	Small, pulses
Proposed function	Regulation	Host defense	Regulation
Activators	Glutamate	Lipopolysaccharide	Acetylcholine
	Noradrenaline

Data adapted from Yun et al (1997) and Moncada et al (1997).