Table 1.

A list of nAChR subunits and representative nAChR subtypes.

Heteromeric nAChR subtypes	Muscle type receptors
	Subunit composition of ligand binding pentamers	Structural subunit
	α1, β, γ, δ (embryonic type); α1, β, ε, δ (adult type)	β (also called β1)
	Neuronal type receptors
	Subunit composition of ligand binding pentamers	Structural subunit
	α2, α3, α4, α5, α6, β2, β3, β4	α5, β3
Homomeric nAChR subtypes	Neuronal type receptors
	α7, α8, α9, α10
Representative nAChR subtypes in CNS	α2β2, α3β2, α3β4, α3β3β4, α4β2, α4α5β2, α6β2β3, α6α4β2β3, α7.

Notes: CNS is the abbreviation of central nervous system. The subunit α8 is currently only found in chick. Those homomeric nAChR subunits, i.e., α10 and α9, may form heteromeric receptors, whereas other three subunits, i.e. α5 and β3 and β1, are able to co-assemble with other subunits as structural subunits.