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-sensiti ve site (PCP site 1) is associated with NMDA receptors, whereas the MK -801-insensitive site (PCP site 2) may be associated with biogenic ami ne transporters (BAT). Although several ''BAT ligands'' are known that bind selectively to PCP site 2 and not to PCP site 1 (such as indatra line), 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 selec tive, high affinity ligand for PCP site 2. We determined the IC50 valu es 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 vari ety of BAT-related measures ([H-3]CFT binding to the DA transporter, [ H-3]nisoxetine binding to the norepinephrine transporter, [H-3]dopamin e uptake, [H-3]serotonin uptake). In addition, we determined the abili ty of RTI-4793-14 to block NMDA responses in cultured hippocampal neur ons under voltage clamp. (+)-MK801 had high affinity for PCP site 1 (4 .6 nM) and potently inhibited NMDA-induced responses, but was much les s 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]nis oxetine 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 cont rast, RTI-4793-14 had high affinity for PCP site 2 (38 nM), low affini ty for PCP site 1 (> 36 mu M), moderate IC(50)s for all BAT-related me asures, and negligible activity at NMDA receptors. Viewed collectively , these data indicate that RTI-4793-14 binds with high affinity and se lectivity to PCP site 2 and provide further support for an association between PCP site 2 and the BATs. (C) 1994 Wiley-Liss, Inc.