Figure 5.

Effect of BAs on [³H]tetracaine (A) and [¹⁴C]amobarbital (B) binding to Torpedo nAChRs in the resting state. Inhibition of [³H]tetracaine (A) or [¹⁴C]amobarbital (B) binding to the resting nAChR elicited by DMXBA or 4OH-DMXBA respectively. nAChR-rich membranes (0.3 µmol·L⁻¹ AChR) were equilibrated (2 h) with 6 nmol·L⁻¹[³H]tetracaine or 13 µmol·L⁻¹[¹⁴C]amobarbital, in the presence of 1 µmol·L⁻¹α-BTx (nAChRs are mainly in the resting state), and increasing concentrations of the BA (e.g. 0.1–1000 µmol·L⁻¹; depending on the experiment type). Non-specific binding was determined in the presence of 100 µmol·L⁻¹ tetracaine or 400 µmol·L⁻¹ amobarbital respectively. The apparent IC₅₀ values for DMXBA and 4OH-DMXBA, the EC₅₀ value for 4OH-DMXBA (A), and the respective n_H values were obtained by non-linear least-squares fit according to eq. 1. In the case of (B), a variable (−) or constant (n_H= 1) n_H value (---) was considered for the sake of comparison. The IC₅₀, EC₅₀ and n_H values are summarized in Table 2. Values shown are the result of one out of two experiments (A) or the mean ± SD from two experiments performed in triplicate (B). 4OH-DMXBA, 3-(4-hydroxy-2-methoxybenzylidene)-anabaseine; α-BTx, α-bungarotoxin; BA, 3-(benzylidene)-anabaseine; DMXBA (or GTS-21), 3-(2,4-dimethoxybenzylidene)-anabaseine; nAChR, nicotinic acetylcholine receptor; n_H, Hill coefficient.