Table S1.

AChR reversal potentials and permeability-coefficient ratios

AChR position –1′ αεαβδ*	Other mutations αεαβδ*	Reversal potential, mean ± SE, mV†	PK+/PCl–, mean ± SE‡	PCl–/PK+, mean ± SE‡	n§
EQEEE	—	−48.7 ± 0.5	97 ± 23	0.022 ± 0.005	20
EQEEE	AAAAA (97/99 ECD)	−49.8 ± 0.3	200 ± 72	0.007 ± 0.003	3
QQQQQ	—	−44.3 ± 0.6	19 ± 2	0.055 ± 0.006	3
AAAAA	—	−44.8 ± 0.8	22 ± 3	0.051 ± 0.008	5
AQAAA	AQAAK (M2 20′)	−43.4 ± 1.1	16 ± 2	0.065 ± 0.011	3
AQAAA	AQAAA (M1–M2 –5′)	−44.8 ± 0.3	20 ± 1	0.050 ± 0.003	4
AQAAA	AQAAK (M2 20′) + AQAAA (M1–M2 –5′)	−41.5 ± 0.5	12 ± 1	0.085 ± 0.005	3
EQEAA	—	−49.4 ± 0.6	88 ± 27	0.007 ± 0.003	4
EAEAA	—	−50.2 ± 0.8	279 ± 222	0.012 ± 0.006	5
AAAEE	—	−49.2 ± 0.5	147 ± 67	0.011 ± 0.004	4
AAADD	—	−45.7 ± 0.9	28 ± 7	0.042 ± 0.009	4
DADAD	—	−47.9 ± 2.3	30	0.040	3
DADDD	—	−47.7 ± 0.5	45 ± 9	0.024 ± 0.004	3
EQEKE	—	−44.8 ± 0.9	21 ± 4	0.050 ± 0.009	3
EQEEK	—	−43.9 ± 0.7	17 ± 2	0.060 ± 0.007	4
AQAEK	—	−36.1 ± 1.4	7.1 ± 1.1	0.16 ± 0.02	6
Steeper gradient
EQEEE	—	−68.7 ± 0.6	110 ± 23	0.010 ± 0.002	4
AAAAA	—	−66.1 ± 1.1	55 ± 15	0.021 ± 0.004	3

^*The amino acids occupying the indicated positions are given for the five muscle-AChR subunits in the order α1, ε, α1, β1, and δ. Mutant residues are given in bold. Positions in and flanking the M2 α-helix are given using the prime notation. ECD, extracellular domain.

^†The equilibrium (Nernst) potentials at 22 °C, calculated using ion activities, were –50.6 mV for K⁺, and +46.2 mV for Cl^–. For the steeper KCl gradient, these values were –71.7 mV for K⁺, and +73.1 mV for Cl^–.

^‡Means and SEs were calculated as described in detail in SI Materials and Methods. Therefore, the mean values of the permeability ratios in this table (columns 4 and 5) are different from the permeability ratios that could be calculated by applying the GHK equation to the mean reversal potentials (column 3).

^§Number of independent whole-cell recordings.