Inhibitory effect of TCAs and (±)-mecamylamine on (±)-epibatidine-induced Ca2+ influx in HEK293 cells expressing human α4β2 AChRs. Increased concentrations of (±)-epibatidine (■) activate the hα4β2 AChR with potency EC50 = 30 ± 5 nM (nH = 1.03 ± 0.04). Subsequently, cells were pre-treated with several concentrations of amitriptyline (○), imipramine (▲), doxepin (●), and (±)-mecamylamine (◇) followed by addition of 0.1 μM (±)-epibatidine. Response was normalized to the maximal (±)-epibatidine response which was set as 100%. The plots are representative of 28 (■), five (●; ○; ▲), and nine (◇) determinations, respectively, where the error bars are S.D. The calculated IC50 and nH values are summarized in Table 1.