Table 2

Inhibition of 5-[125I]iodo-A-85380 binding by nAChR and non-nAChR ligands

nAChR LigandsKi, nMNon-nAChR LigandsKi, nM
 (−)-Epibatidine0.009  ± 0.001Physostigmine>25,000
 5-Iodo-A-853800.010  ± 0.001DFP>1,000,000
 A-853800.015  ± 0.002Naloxone>25,000
 (−)-Cytisine0.16  ± 0.02Apomorphine>25,000
 (−)-Nicotine0.96  ± 0.06Haloperidol>25,000
 Acetylcholine4.0  ± 0.1
 (+)-Nicotine10  ± 1
 Carbachol73  ± 6
 Dihydro-β-erythroidine7.4  ± 0.8
 Curare730  ± 70
 α-Bungarotoxin  >2,500

Rat brain P2 membrane fractions (10–11 μg of protein) were incubated in a total volume of 0.2 ml with 130 pM 5-[125I]iodo-A-85380 and 9 to 11 concentrations of competitors for 4 h at 22°C and analyzed as described in Experimental Procedures. The inhibition constants (K i values) were calculated by the Cheng-Prusoff equation from measured IC50 values using aK d value of 10 pM for 5-[125I]iodo-A-85380 binding. In all assays, the pseudo-Hill coefficients (nH ) did not differ significantly from 1. Data represent mean ± S.E. obtained from four to six experiments per compound. Experiments were performed in duplicate.