Figure 6.

Potencies of PeIA and analogues for rat α6β4 nAChRs are similar to those for the α6/α3β4 chimera. X. laevis oocytes expressing rat α6β4 nAChRs were subjected to TEVC electrophysiology and the IC₅₀ values for inhibition of ACh-evoked currents by PeIA and select analogues determined as described in the Experimental Section. Effects of the α3 transmembrane domain on ligand binding to α6β4 nAChRs were assessed by expressing nonchimeric α6 subunits with β4 subunits. PeIA, [Val⁷]PeIA, [Asn⁹]PeIA, [Arg¹¹]PeIA, and [Ile¹⁵]PeIA were tested for inhibition of α6β4 and the IC₅₀ values compared to those obtained for rat α6/α3β4 nAChRs (see Tables 2 and4). The IC₅₀ value for inhibition of ACh-evoked currents by native PeIA was 222 (189–262) nM (n = 5). The IC₅₀ values (nM) for [Val⁷]PeIA, [Asn⁹]PeIA, [Arg¹¹]PeIA, and [Ile¹⁵]PeIA were 27.2 (22.9–32.2) (n = 4), 17.2 (14.9–20.1) (n = 4), 23.3 (20.1–27.1) (n = 4), and 49.7 (43.8–56.3) (n = 4), respectively. The IC₅₀ values for inhibition of α6β4 and α6/α3β4 nAChRs were <2-fold different for all tested peptides. The peptides are rank-ordered from top to bottom by potency. Values within parentheses indicate the 95% CI of the IC₅₀ estimate, and the error bars indicate the SD of the data. The curve for [Arg¹¹]PeIA is shown offset slightly to avoid overlap.