TMA⁺ conduction through the muscle nAChR and GLIC. (A and B) Macroscopic current responses to 1-ms pulses of 142 mM TMA⁺ recorded at –80 mV from the wild-type (A) and the εT12′P slowly deactivating mutant (B) of the mouse muscle adult-type nAChR in the outside-out configuration. The TMA⁺-containing solution was (in mM) 142 TMACl and 10 HEPES/TMAOH, pH 7.4, whereas the TMA⁺-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 TMA⁺. (C) Macroscopic current response to a 100-ms pulse of pH-4.5 solution (pH_holding 7.4) containing 142 mM TMA⁺ recorded at –80 mV from GLIC in the outside-out configuration. The TMA⁺-containing solution was (in mM) 142 TMACl and 10 acetic acid/TMAOH, pH 4.5, whereas the TMA⁺-free solution was (in mM) 142 KCl, 5.4 NaCl, 1.8 CaCl₂, 1.7 MgCl₂, and 10 HEPES/KOH, pH 7.4. The short duration of the pH-4.5-solution application ensured that entry into desensitization within the pulse was negligible. All other conditions are as in A and B. (D) Intra–pulse-to-tail current ratios. The plotted values are means obtained from 17 (wild-type nAChR), 11 (εT12′P nAChR), and 6 (GLIC) patches; error bars are the corresponding standard errors. All current traces shown in this figure are the averages of 10 consecutive responses recorded from representative patches.