α-Conotoxin BuIA[T5A;P6O]: a novel ligand that discriminates between α6ß4 and α6ß2 nicotinic acetylcholine receptors and blocks nicotine-stimulated norepinephrine release.
α6* (asterisk indicates the presence of additional subunits) nicotinic acetylcholine receptors (nAChRs) are broadly implicated in catecholamine-dependent disorders that involve attention, motor movement, and nicotine self-administration. Different molecular forms of α6 nAChRs mediate catecholamine release, but receptor differentiation is greatly hampered by a paucity of subtype selective ligands. α-Conotoxins are nAChR-targeted peptides used by Conus species to incapacitate prey. We hypothesized that distinct conotoxin-binding kinetics could be exploited to develop a series of selective probes to enable study of native receptor subtypes. Proline6 of α-conotoxin BuIA was found to be critical for nAChR selectivity; substitution of proline6 with 4-hydroyxproline increased the IC(50) by 2800-fold at α6/α3β2β3 but only by 6-fold at α6/α3β4 nAChRs (to 1300 and 12 nM, respectively). We used conotoxin probes together with subunit-null mice to interrogate nAChR subtypes that modulate hippocampal norepinephrine release. Release was abolished in α6-null mutant mice. α-Conotoxin BuIA[T5A;P6O] partially blocked norepinephrine release in wild-type controls but failed to block release in β4(-/-) mice. In contrast, BuIA[T5A;P6O] failed to block dopamine release in the wild-type striatum known to contain α6β2* nAChRs. BuIA[T5A;P6O] is a novel ligand for distinguishing between closely related α6* nAChRs; α6β4* nAChRs modulate norepinephrine release in hippocampus but not dopamine release in striatum.
Azam
Layla
L
Department of Biology, University of Utah, Salt Lake City, UT 84112, USA. layla.azam@utah.edu
Maskos
Uwe
U
Changeux
Jean-Pierre
JP
Dowell
Cheryl D
CD
Christensen
Sean
S
De Biasi
Mariella
M
McIntosh
J Michael
JM
D000818:Animals; D020916:Conotoxins / Q000378:metabolism*; D005260:Female; D006900:Hydroxylation; D008024:Ligands; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009538:Nicotine / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D011392:Proline / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000378:metabolism*; D014981:Xenopus
D020916:Conotoxins; D008024:Ligands; D011978:Receptors, Nicotinic; C104518:nicotinic receptor alpha6; D009538:Nicotine; D011392:Proline; D009638:Norepinephrine