Fig. 2.

κM-RIIIJ displays enhanced apparent affinity toward asymmetric K_v1 channels. (A) Western blot analysis of selected concatemeric constructs expressed in HEK293. Bands corresponding to 75-, 150-, and 300-kDa protein products were recognized by an anti-Kv1.2 antibody evidencing expression of monomeric, dimeric, and tetrameric channels, respectively. (B) Representative current traces of symmetric heterodimeric and asymmetric heterotetrameric channels composed of K_v1.2 and K_v1.6. The effect of 0.5 nM (red) and 5 nM (blue) κM-RIIIJ on evoked K⁺ currents from K_v1.6/1.2 dimer and tetrameric concatemers composed of three K_v1.2 subunits and one K_v1.6 subunit are shown (black: control). The zero current level is marked by the dashed line. (Scale bars, 1 nA and 50 ms.) (C) IC₅₀s of κM-RIIIJ block of homomeric and heteroconcatemeric K_v1 channels formed by K_v1.1, K_v1.2, and K_v1.6 subunits in different combinations. κM-RIIIJ displayed extremely high apparent affinity (sub-nM) for asymmetric concatemers composed of one K_v1.1 or K_v1.6 subunit together with three K_v1.2 subunits (SI Appendix, Table S2).