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 2a analogs having alkyl or phenyl plus alkyl substitutions (compounds 2y, 2o, 2w, and 2x) as indicated. Mean micromolar IC50 values and SEM as a multiplication/division factor of the mean micromolar IC50 value are provided in Table 1.