Figure 4

Effect of globular and ribbon isomers of α-conotoxin BuIA at nAChR subtypes expressed in Xenopus oocytes. (A)Representative ACh-evoked currents mediated by α3β2 and α3β4 nAChR subtypes obtained in the absence (control) and presence of 10 nM and 100 nM BuIA-globular, respectively. Complete recovery was observed after 10 min washout (broken line). (B)Concentration-response curves for the inhibition of α3β2 and α3β4 nAChRs by globular (filled symbols) and ribbon (open symbols) isomers of BuIA. Best fit of the data gave IC₅₀ values of 4.8 ± 0.4 nM (n_H = 1.3) and 59.1 ± 2.3 nM (n_H = 1.2) for α3β2 and α3β4 nAChRs, respectively, whereas the ribbon isomer of BuIA exhibited no inhibition at 1 μM. Responses are shown as a percentage of ACh (100 μM)-induced peak current amplitude after a 5 min incubation of the BuIA isomers with respect to control (ACh alone). Error bars are SEM with n = 4–7 for each data point.