[³H]2-nitroimipramine: A selective "slowly-dissociating" probe of the imipramine binding site ("serotonin transporter") in platelets and brain

Previous studies have demonstrated a close functional and structural relationship between the "high affinity" binding site for [³H]imipramine and the presynaptic and platelet uptake site(s) for serotonin. Recently we have synthesized several nitro derivatives of imipramine which have a very high affinity for the imipramine binding site and which dissociate very slowly when incubations are performed at 0-4°C. In this report, we describe the characteristics of [³H]2-nitroimipramine binding to platelet and brain membranes. Our results support the relative utility of this ligand for studying the impramine binding site (serotonin transporter) since this analogue has both a higher affinity and specific activity than [³H]imipramine. [³H]2-Nitroimipramine by virtue of its extremely slow dissociation rate should be a valuable tool in subsequent characterization and purification of the serotonin uptake or transport site.