Specific 86Rb+ efflux (ordinate; percentage of control) was determined for functional, human ganglionic α3β4*-nAChR naturally expressed by SH-SY5Y human neuroblastoma cells in the presence of the full agonist, carbamylcholine, at the indicated concentrations (abscissa, log molar) either alone (■) or in the presence of 10 μM 3-phenyltropane analogues 4b (△), 4c (□), 4e (▼), or 4f (●) as indicated. The reduction of apparent agonist efficacy without an effect on potency is consistent with a noncompetitive mechanism for nAChR block.