sample="supplemental" bates="HK1360117" isource="ctr" decade="1980" class="ue" date="19810723" The Council For Tobacco Research - U.S.A., Inc. PUBLICATION BY GRANTEE (1923) The following paper has been published with acknowledgment of support by The Council for Tobacco Research - U.S.A., Inc. A TERBIUM-160 PROBE OF THE NICOTINIC BINDING SITE OF THE ACETYLCHOLINE RECEPTOR FROM TORPEDO CALIFORNICA Trivalent terbium, which is known to be able to substitute for Ca(II) at specific sites on the acetylcholine receptor was used here as a prove of the nicotinic binding site of the acetylcholine receptor from Torpedo californica. In this paper, the ability of various ligands to displace 160Tb(III) bound to the acetylcholine receptor from Torpedo californica is described. Specifically, ligand-induced 160Tb(III) displacement was followed in a specifically designed flow dialysis apparatus, coupled to a NaI(TI) -ray scintillation spectrometer. This displacement was monitored as a function of (1) the concentration of nicotinic ligand (i.e., acetylcholine chloride) in the "wash-out" buffer and (2) the nature of the nicotinic ligand in the buffer (e.g., acetylcholine chloride, tetreethylammonium bromide and nikethamide). Measured 160Tb(III) exchange half-lives indicate (1) a direct relationship between 160Tb(III) displacement and nicotinic ligand concentration in the "wash-out" buffer and (2) an enhanced 160Tb(III) displacement for nicotinic and agents possessing quaternary ammonium functions (e.g., acetylcholine chloride and tetraethylammonium bromide) versus neutral ligands (e.g., nukethemide). Lancione, G. V., Nelson, D. J., and Wright, G. M. Inorganic Chimica Acta 55:71-75, 1981. From the Department of Chemistry, Jeppson Laboratory, Worcestor, Mass., and the Department of Pharmacology, University of Massachusetts Medical Center, Worcester. DBC