Block of the muscle nAChR by TEA⁺. (A) Macroscopic current responses to 2-s pulses of 100 µM ACh recorded at –80 mV from the mouse muscle adult-type nAChR in the outside-out configuration. The response of each patch of membrane was recorded sequentially in the absence of TEA⁺ (left), in the presence of 0.5 mM TEA⁺ flowing through both barrels of the theta-type perfusion tubing (middle), and back again, without TEA⁺ in either barrel (right). The solutions flowing through the two barrels of the perfusion tubing were (in mM) 142 KCl, 5.4 NaCl, 1.8 CaCl₂, 1.7 MgCl₂, and 10 HEPES/KOH, pH 7.4 with or without ACh and with or without TEA⁺. In the schematic representations of the theta-tubing perfusion, arrows indicate the application of TEA⁺. Note the expanded current scale used for the middle panel; the trace is the average of 25 consecutive responses recorded from a representative patch. (B) Single-channel inward currents elicited by 100 µM ACh recorded in the presence or absence of 0.5 mM TEA⁺ at approximately –80 mV in the cell-attached configuration; openings are downward deflections. The pipette solution was (in mM) 142 KCl, 5.4 NaCl, 1.8 CaCl₂, 1.7 MgCl₂, 0.1 ACh, and 10 HEPES/KOH, pH 7.4 with or without TEA⁺. (C) Peak-current amplitudes recorded in response to the application of ACh in the presence of external 0.5 mM or 5.0 mM TEA⁺ and upon TEA⁺ removal normalized to the peak value observed in the initial TEA⁺-free recording. (D) Time constant of desensitization during the application of ACh in the presence of external 0.5 or 5.0 mM TEA⁺ and upon TEA⁺ removal normalized to the time constant fitted to the initial TEA⁺-free recording. The values plotted in C and D are means obtained from six patches each for the two concentrations of TEA⁺; error bars are the corresponding standard errors.