TEA⁺–K⁺ competition in ELIC. (A and B) Macroscopic current responses to 500-ms pulses of 10 mM cysteamine plus 142 mM TEA⁺ recorded at –80 mV from the wild type (A) and the L9′A + F16′L wider-pore mutant (B) in the outside-out configuration. The TEA⁺-containing solution was (in mM) 142 KCl, 142 TEACl, 10 cysteamine, and 10 HEPES/KOH, pH 7.4, whereas the TEA⁺-free solution was (in mM) 142 KCl and 10 HEPES/KOH, pH 7.4. In the schematic representations of the theta-tubing perfusion, arrows indicate the application of TEA⁺. (C) Intra–pulse-to-tail current ratios. The plotted values are means obtained from 9 (wild type) and 3 (L9′A + F16′L mutant) patches; error bars are the corresponding standard errors. Both current traces shown in this figure are the averages of 10 consecutive responses recorded from two representative patches.