Specific 86Rb+ efflux (ordinate; percentage of control) was determined for functional, human muscle-type α1β1γδ-nAChR (■), ganglionic α3β4*-nAChR (○), α4β2-nAChR (▲), or α4β4-nAChR (∇) naturally or heterologously expressed in human cell lines in the presence of a receptor subtype-specific, EC80–EC90 concentration of the full agonist, carbamylcholine, either alone or in the presence of the indicated concentrations (abscissa, log molar) of (S,S)-5a, (R,R)-5a, 5e, or 5f as indicated. Mean micromolar IC50 values and SEM as a multiplication/division factor of the mean micromolar IC50 value are provided in Table 1.