RTI-4793-14, A NEW LIGAND WITH HIGH-AFFINITY AND SELECTIVITY FOR THE (+)-MK801-INSENSITIVE [H-3] 1-[1-(2-THIENYL)CYCLOHEXYL]PIPERIDINE BINDING-SITE (PCP SITE-2) OF GUINEA-PIG BRAIN

[H-3]]TCP, an analog of the dissociative anesthetic phencyclidine (PCP), binds with high affinity to two sites in guinea pig brain membranes, one that is MK-801 sensitive and one that is not. The MK-801-sensitive site (PCP site 1) is associated with NMDA receptors, whereas the MK-801-insensitive site (PCP site 2) may be associated with biogenic amine transporters (BAT). Although several ''BAT ligands'' are known that bind selectively to PCP site 2 and not to PCP site 1 (such as indatraline), these compounds have low affinity for site 2 (K-i values > 1 mu M). Here we demonstrate that the novel pyrrole RTI-4793-14 is a selective, high affinity ligand for PCP site 2. We determined the IC50 values of RTI-4793-14 and several reference compounds [PCP, (+)-MK801 and indatraline] for PCP site 1 (assayed with [H-3](+)-MK801), PCP site 2 (assayed with [H-3]TCP in the presence of 500 nM (+)-MK801) and a variety of BAT-related measures ([H-3]CFT binding to the DA transporter, [H-3]nisoxetine binding to the norepinephrine transporter, [H-3]dopamine uptake, [H-3]serotonin uptake). In addition, we determined the ability of RTI-4793-14 to block NMDA responses in cultured hippocampal neurons under voltage clamp. (+)-MK801 had high affinity for PCP site 1 (4.6 nM) and potently inhibited NMDA-induced responses, but was much less potent in the BAT-related measures (IC(50)s > 10 mu M). PCP had high affinity at PCP site 1 (IC50 = 92 nM) and PCP site 2 (IC50 = 117 nM), and was moderately potent in all BAT-related measures except [H-3]nisoxetine binding. Indatraline was potent in BAT-related measures (IC(50)s, 2 to 5 nM), but weak in other measures (IC(50)s > 1 mu M). In contrast, RTI-4793-14 had high affinity for PCP site 2 (38 nM), low affinity for PCP site 1 (> 36 mu M), moderate IC(50)s for all BAT-related measures, and negligible activity at NMDA receptors. Viewed collectively, these data indicate that RTI-4793-14 binds with high affinity and selectivity to PCP site 2 and provide further support for an association between PCP site 2 and the BATs. (C) 1994 Wiley-Liss, Inc.*