Figure 2.

(A) Effects of LF-3-88 at nAChR subtypes. Specific ⁸⁶Rb⁺ efflux (ordinate; percentage of control ± SEM) was determined as described in the Materials and Methods for intrinsic agonist activity over a 9.5 min period for compound LF-3-88 at the indicated concentrations (abscissa; log molar scale) on human α4β2-nAChR (●), (α6/3)β2β3-nAChR (▼), α3β4*-nAChR (♦), or α1β1γδ-nACHR (▲) naturally or heterologously expressed by SH-EP1-hα4β2, SH-EP1-h(α6/3)β2β3, SH-SY5Y, or TE671/RD cells, respectively. Also shown are functional inactivation effects of pretreatment for 10 min with the same agents at the indicated concentrations on subsequent agonist action of an EC₉₀ concentration of the full agonist, carbamylcholine (applied in the continuing presence of the indicated agents), acting at α4β2-nAChR (○), (α6/3)β2β3-nAChR (▽), α3β4*-nAChR (♢), or α1β1γδ-nAChR (△). Results are normalized to responses to a fully efficacious concentration of carbamylcholine (see Materials and Methods for details). Nanomolar agonist EC₅₀ values and inactivation IC₅₀ values are provided in Table 2, as are agonism and inactivation efficacies (normalized to those for a full agonist or antagonist, respectively). (B) The unusual characteristic of sazetidine-A being a full agonist at HS α4β2-nAChRs while having zero or nearly zero efficacy at LS α4β2-nAChRs allows the determination of a ligand's efficacies at both HS- and LS-α4β2 in cells expressing a variable mix of the two α4β2-nAChR isoforms. The ordinate intercepts of the linear regressions at a sazetidine-A efficacy (abscissa) of 0% represent the efficacies at LS α4β2-nAChRs, while the ordinate intercepts at a sazetidine-A efficacy of 100% represent the efficacies at HS α4β2-nAChRs. Values and standard errors are reported in Table 2.