Multiple binding sites for [I-125]RTI-121 and other cocaine analogs in rat frontal cerebral cortex
Boja, J. W., Carroll, F., Vaughan, R. A., Kopajtic, T., & Kuhar, M. J. (1998). Multiple binding sites for [I-125]RTI-121 and other cocaine analogs in rat frontal cerebral cortex. Synapse, 30(1), 9-17.
In an effort to identify novel binding sites for cocaine and its analogs, we carried out binding studies with the high-affinity and selective ligand [I-125]RTI-121 in rat frontal cortical tissue. Very low densities of binding sites were found. Saturation analysis revealed that the binding was to both high- and low-affinity sites. Pharmacological competition studies were carried out with inhibitors of the dopamine, norepinephrine, and serotonin transporters. The various transporter inhibitors inhibited the binding of 15 pM [I-125]RTI-121 in a biphasic fashion following a two-site binding model. The resultant data were complex and did not suggest a simple association with any single transporter. Correlational analysis supported the following hypothesis: [I-125] RTI-121 binds to known transporters and not to novel sites; these include dopamine, norepinephrine, and serotonin transporters. Immunoprecipitation of transporters photoaffinity labeled with [(125)] RTI-82 and subsequent analysis of SDS-page gels revealed the presence of authentic dopamine transporters in these samples; displacement of the photoaffinity label occurred with a typical dopamine transporter pharmacology. These data are compatible with the binding properties of RTI-181 and the presence of several known transporters in the tissue studied. Synapse 30:9-17, 1998. (C) 1998 Wiley-Liss, Inc.