Varenicline is a partial agonist at alpha4beta2 and a full agonist at alpha7 neuronal nicotinic receptors.
Varenicline, a new nicotinic ligand based on the structure of cytisine, has recently been approved by the U.S. Food and Drug Administration for use as a smoking cessation aid. Varenicline has been shown to be a partial agonist of alpha4beta2 receptors, and in equilibrium binding assays, it is highly selective for the alpha4beta2 receptor. In this study, we have examined the functional activity of varenicline at a variety of rat neuronal nicotinic receptors expressed in Xenopus laevis oocytes and assayed under two-electrode voltage clamp. We also find that varenicline is a potent, partial agonist at alpha4beta2 receptors, with an EC50 of 2.3 +/- 0.3 microM and an efficacy (relative to acetylcholine) of 13.4 +/- 0.4%. Varenicline has lower potency and higher efficacy at alpha3beta4 receptors, with an EC50 of 55 +/- 8 microM and an efficacy of 75 +/- 6%. Varenicline also seems to be a weak partial agonist at alpha3beta2 and alpha6-containing receptors, with an efficacy <10%. It is remarkable that varenicline is a potent, full agonist at alpha7 receptors with an EC50 of 18 +/- 6 microM and an efficacy of 93 +/- 7% (relative to acetylcholine). Thus, whereas varenicline is a partial agonist at some heteromeric neuronal nicotinic receptors, it is a full agonist at the homomeric alpha7 receptor. Some combination of these actions may be involved in the mechanism of varenicline as a smoking cessation aid.
Mihalak
Karla B
KB
Department of Molecular and Cellular Pharmacology (R-189), University of Miami Miller School of Medicine, PO Box 016189, Miami, FL 33101, USA.
Carroll
F Ivy
FI
Luetje
Charles W
CW
D000818:Animals; D001552:Benzazepines / Q000737:chemistry / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018722:Nicotinic Agonists / Q000737:chemistry / Q000494:pharmacology*; D009865:Oocytes / Q000187:drug effects; D011810:Quinoxalines / Q000737:chemistry / Q000494:pharmacology*; D051381:Rats; D011978:Receptors, Nicotinic / Q000378:metabolism*; D000068580:Varenicline; D014982:Xenopus laevis; D064569:alpha7 Nicotinic Acetylcholine Receptor
D001552:Benzazepines; C579165:Chrna7 protein, rat; D018722:Nicotinic Agonists; D011810:Quinoxalines; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; C403531:nicotinic receptor alpha4beta2; D000068580:Varenicline