Sazetidine-A Is a Potent and Selective Agonist at Native and Recombinant α4β2 Nicotinic Acetylcholine Receptors

Abstract

Sazetidine-A has been recently proposed to be a "silent desensitizer" of ␣4␤2 nicotinic acetylcholine receptors (nAChRs), implying that it desensitizes ␣4␤2 nAChRs without first activating them. This unusual pharmacological property of sazetidine-A makes it, potentially, an excellent research tool to distinguish between the role of activation and desensitization of ␣4␤2 nAChRs in mediating the central nervous system effects of nicotine itself, as well as those of new nicotinic drugs. We were surprised to find that sazetidine-A potently and efficaciously stimulated nAChR-mediated dopamine release from rat striatal slices, which is mediated by ␣4␤2* and ␣6␤2* subtypes of nAChR. The agonist effects on native striatal nAChRs prompted us to re-examine the effects of sazetidine-A on recombinant ␣4␤2 nAChRs in more detail. We expressed the two alternative stoichiometries of ␣4␤2 nAChR in Xenopus laevis oocytes and investigated the agonist properties of sazetidine-A on both ␣4(2)␤2(3)and ␣4(3)␤2(2) nAChRs. We found that sazetidine-A potently activated both stoichiometries of ␣4␤2 nAChR: it was a full agonist on ␣4(2)␤2(3) nAChRs, whereas it had an efficacy of only 6% on ␣4(3)␤2(2) nAChRs. In contrast to what has been published before, we therefore conclude that sazetidine-A is an agonist of native and recombinant ␣4␤2 nAChRs but shows differential efficacy on ␣4␤2 nAChRs subtypes.

Elucidation of Molecular Impediments in the α6 Subunit for in Vitro Expression of Functional α6β4* Nicotinic Acetylcholine Receptors

“…As for the other agonists, the partial agonist activity of (Ϫ)-cytisine at C6 F223L ␤4␤3 is in concordance with previous studies of the agonist at chick ␣6-human ␤4 and ␣3␤4 nAChRs (21, 34 -36) just as the 32% efficacy exhibited by varenicline seems plausible considering its partial agonist activity at ␣4␤2, ␣3␤4, and ␣6 NTD /␣3 TMD/ICL ␤2␤3 nAChRs (37,38). Finally, the biphasic concentration-response relationship exhibited by sazetidine A seems plausible in light of previous reports of sazetidine A being a potent agonist and desensitizing agent of ␣4␤2 nAChRs (39,40). Finally, although the determined IC 50 value of 60 nM for mecamylamine at C6 F223L ␤4␤3 admittedly is in the low end of IC 50 values reported for the antagonist at heteromeric nAChRs (2), the antagonist has displayed comparable antagonist potencies at ␣3␤4 nAChRs in some studies (41,42).…”

α6β2* and α4β2* Nicotinic Acetylcholine Receptors As Drug Targets for Parkinson's Disease

“…Quik, unpublished observations). Sazetidine-A, another agent initially reported as selective for ␣4␤2* receptors, binds with high affinity to ␣6␤2* nAChRs and stimulates both ␣4␤2* and ␣6␤2* nAChR-mediated dopamine release (Xiao et al, 2006;Cucchiaro et al, 2008;Zwart et al, 2008;M. Quik, unpublished observations).…”

Acetylcholine-Binding Protein Engineered to Mimic the α4-α4 Binding Pocket in α4β2 Nicotinic Acetylcholine Receptors Reveals Interface Specific Interactions Important for Binding and Activity

“…1A). Interestingly, this has been shown to influence agonist sensitivities (Nelson et al, 2003;Moroni et al, 2006;Zwart et al, 2008;Carbone et al, 2009) and calcium ion permeability (Tapia et al, 2007) and cause distinctly different pharmacology (Nelson et al, 2003;Kuryatov et al, 2005;Moroni et al, 2006Moroni et al, , 2008Tapia et al, 2007). The two receptor stoichiometries were recently found to differ in the number of agonist binding sites.…”