AT-1001 Is a Partial Agonist with High Affinity and Selectivity at Human and Rat a3b4 Nicotinic Cholinergic Receptors

AT-1001 [N-(2-bromophenyl)-9-methyl-9-azabicyclo[3.3.1] nonan3-amine] is a high-affinity and highly selective ligand at a3b4 nicotinic cholinergic receptors (nAChRs) that was reported to decrease nicotine self-administration in rats. It was initially reported to be an antagonist at rat a3b4 nAChRs heterologously expressed in HEK293 cells. Here we compared AT-1001 actions at rat and humana3b4 and a4b2 nAChRs similarly expressed in HEK 293 cells. We found that, as originally reported, AT-1001 is highly selective for a3b4 receptors over a4b2 receptors, but its binding selectivity is much greater at human than at rat receptors, because of a higher affinity at human than at rat a3b4 nAChRs. Binding studies in human and rat brain and pineal gland confirmed the selectivity of AT-1001 for a3b4 nAChRs and its higher affinity for human compared with rat receptors. In patch-clamp electrophysiology studies, AT-1001 was a potent partial agonist with 65–70% efficacy at both human and rat a3b4 nAChRs. It was also a less potent and weaker (18%) partial agonist at a4b2 nAChRs. Both a3b4 and a4b2 nAChRs are upregulated by exposure of cells to AT-1001 for 3 days. Similarly, AT-1001 desensitized both receptor subtypes in a concentration-dependent manner, but it was 10 and 30 times more potent to desensitize human a3b4 receptors than rat a3b4 and human a4b2 receptors, respectively. After exposure to AT-1001, the time to recovery from desensitization was longest for the human a3b4 nAChR and shortest for the human a4b2 receptor, suggesting that recovery from desensitization is primarily related to the dissociation of the ligand from the receptor.