TPA⁺–K⁺ competition and TPA⁺ conduction through ELIC. (A and B) Macroscopic current responses to 500-ms pulses of 10 mM cysteamine plus 142 mM TPA⁺ recorded at –80 mV from the wild type in the outside-out configuration. In (A), the TPA⁺-containing solution was (in mM) 142 KCl, 142 TPACl, 10 cysteamine, and 10 HEPES/KOH, pH 7.4, whereas the TPA⁺-free solution was (in mM) 142 KCl and 10 HEPES/KOH, pH 7.4. In (B), the TPA⁺-containing solution was (in mM) 142 TPACl, 10 cysteamine, and 10 HEPES/TPAOH, pH 7.4, whereas the TPA⁺-free solution was (in mM) 142 KCl, 5.4 NaCl, 1.8 CaCl₂, 1.7 MgCl₂, and 10 HEPES/KOH, pH 7.4. In the schematic representations of the theta-tubing perfusion, arrows indicate the application of TPA⁺. (C) Intra–pulse-to-tail current ratios. The plotted values are means obtained from 5 patches for each condition; 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.