NeuropharmacologyHigh affinity binding of [3H]epibatidine to rat brain membranesGnädisch, Daniela1; London, Edythe D.1; Terry, Phyllis1; Hill, Geraldine R.1; Mukhin, Alexey G.1,2Author Information 1Brain Imaging Center, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, 5500 Nathan Shock Drive, Baltimore, MD 21224, USA 2Corresponding Author: Alexey G. Mukhin ACKNOWLEDGEMENTS: We thank Drs D. Bruce Vaupel and Andrei O. Koren for advising and consulting with us. The generous gift of IPH provided by Dr Kenneth J. Kellar is gratefully acknowledged. We also thank Ms Cindy Ambriz for excellent administrative and secretarial assistance. Received 17 February 1999; accepted 26 March 1999 NeuroReport: June 3rd, 1999 - Volume 10 - Issue 8 - p 1631-1636 Buy Abstract SEVERAL compounds, such as epibatidine, A-85380, and their analogs, have been identified recently as nAChR ligands whose affinities lie in the low picomolar range. Accurate measurement of such high affinities is fraught with certain technical difficulties, which may account for the inconsistency of previously reported affinities of epibatidine, ranging from 4 to 60 pM. Here, we demonstrate that (±)-[3H]epibatidine (1–500 pM) binds to a single population of sites in rat brain with KD of 8 ± 2 pM. This affinity was confirmed in both kinetic experiments and competition assays with (±)-[3H]epibatidine and (−)-[3H]cytisine, which were performed under experimental conditions developed specifically for ligands with subnanomolar affinities. Variations from these conditions decreased the observed affinities. NeuroReport 10:1631–1636 © 1999 Lippincott Williams & Wilkins. © 1999 Lippincott Williams & Wilkins, Inc.