Fig. 5.

ACh activation of wild-type versus mutant LSP α4β2-nAChR. X. laevis oocytes injected with unmodified or mutant LSP mRNA were exposed to acute ACh challenges (1 second, concentrations specified on the x axis; log M scale). Filled symbols show concentration-response relationships determined for each LSP variant when exposed to acute ACh stimulation. Note that the proportion of HS-phase function is enhanced for every LSP mutant compared with the unmodified LSP construct. Open symbols depict concentration-response determinations for the same constructs, when exposed to a range of ACh concentrations after 5-minute preincubation with Saz-A (3.16 nM, 5 minutes). Pretreatment with Saz-A reduced HS-phase function of all LSP variants to such an extent that it could no longer be fit as part of a two-site model, leaving only LS-phase function. Log EC₅₀ values for HS- and LS-phase responses, fractions of HS- versus LS-phase function, and statistical analyses are reported in Table 1. Points are the mean ± S.E.M. (n = 6–12).