Switching the C terminus of Kir1.1 to that of Kir2.1 (C13 chimera) increases the affinity of block by Mg²⁺ and TEA⁺. Typical current traces at two voltages with and without blockers are shown at the top of each panel. Block was analyzed according to Eq. 3 at extracellular K⁺ concentrations of 11 mM for (A) 0.2 mM Mg²⁺, (B) 40 mM Na⁺, and (C) 0.01 mM TEA⁺. Values of K_i(0) decreased from 0.82 to 0.16 mM (Mg²⁺), 117 to 77 mM (Na⁺), and 1.8 to 0.05 mM (TEA⁺). No significant differences in zδ were observed for Na⁺, or Mg²⁺, or TEA⁺ measured from changes in i, but zδ for TEA⁺ block measured as P_o was 1.63.