α-Conotoxin BuIA is a paralytic peptide neurotoxin and a competitive nAChR antagonist, with IC 50 s of 0.258 nM (α6/α3β2), 1.54 nM (α6/α3β4), 5.72 nM (α3β2), respectively. α-Conotoxin BuIA can be used to distinguish nAChRs containing β2- and β4-subunit, respectively. α-Conotoxin BuIA distinguishes among αxβ2 nAChRs with a rank order potency of α6>α3>α2>α4.