High affinity binding of [H-3]epibatidine to rat brain membranes

SEVERAL compounds, such as epibatidine, A-85380, and their analogs, have be en identified recently as nAChR ligands whose affinities lie in the low pic omolar 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. Her e, we demonstrate that (+/-)-[H-3]epibatidine (1-500 pM) binds to a single population of sites in rat brain with K-D of 8+/-2 pM. This affinity was co nfirmed in both kinetic experiments and competition assays with (+/-)[H-3]e pibatidine and (-)-[H-3]cytisine, which were performed under experimental c onditions developed specifically for ligands with subnanomolar affinities. Variations from these conditions decreased the observed affinities. NeuroRe port 10:1631-1636 (C) 1999 Lippincott Williams & Wilkins.