Recombinant Kv1 channels assembled on the surface of mammalian cells in active form. (A) Saturable binding (▾) of ¹²⁵I-αDTX to intact HEK-293 cells, expressing Kv1.1-1.1-1.2-1.2, quantified by a filtration assay. Relatively low values were recorded for nonsaturable (▴) binding compared with total (▪). Inset shows a Scatchard plot of the saturable binding. (B) Competition of 2.5 nM ¹²⁵I-αDTX binding to cells transfected (as in A) by αDTX, DTX_k, or TsTx-Kα, which gave respective mean values for Ki of 0.6, 2.0, and 0.1 nM (error bars are ± SD; n = 4). (C) Antagonism of 2.5 nM ¹²⁵I-αDTX binding to cells expressing Kv1.1-1.1-1.2-1.2 (▪) or Kv1.2-1.1-1.2-1.1 (▴) channels by KTX gave respective IC₅₀ values of 12.4 ± 0.2 and 5.6 ± 0.1 nM (mean ± SD; n = 3).