External Na⁺ and Li⁺ block K⁺ currents through Kir1.1 channels. (A) Currents at different voltages in the presence of 11 mM K⁺ in the pipette solution and 110 mM K⁺ in the bath solution. (B) Currents under the same conditions as in A but with 99 mM Na⁺ in the pipette solution. (C) i-V relationships in the absence of blockers and in the presence of 99 mM Na⁺ or Li⁺ in the external solution. (D) Analysis of block by external Na⁺ and Li⁺ according to Eqs. 2 and 3. The lines represent best fits to the data, with K_iNa = 272 mM and zδ_Na = 0.15, and K_iLi = 203 mM and zδ_Li = 0.17.