Figure 2.

Quinacrine inhibition of ACh-induced currents in Cys mutants is shown. (A) An oocyte expressing wild-type receptor was treated sequentially with 1 μM ACh and 0, 0.1, 0.2, 0.5, 1, 2, 5, and 10 μM quinacrine (bar). After 7 s, the oocyte was washed with CFFR for 180 s. The sequential responses are superimposed in the plot. The maximum current during the 7 s was taken as the response. These responses are plotted in the Inset and are fit by I = I₀/(1 + q/IC₅₀), where I is the current, I₀ is the current at zero quinacrine, and q is the quinacrine concentration. (B) The IC₅₀ for quinacrine of the mutants is normalized by the IC₅₀ of wild type (2.7 ± 0.2 μM). (C) The IC₅₀ for QX-314 of the mutants is normalized by the IC₅₀ of wild type (78 ± 12 μM), and the EC₅₀ for ACh of the mutants is normalized by the EC₅₀ of wild type (2.6 ± 0.4 μM). The IC₅₀ values for QX-314 for all mutants except Y213C and V218C were from ref. 38. The EC₅₀ was from refs. 14 and 24.