Table 1.

Boltzmann parameters of activation relationships of different ClC-1 variants using various internal chloride concentrations.

Variant	[Cl−]i (mM)	N	V0.5 (mV)	S	Min
WT	134	15	− 69.2 ± 2.3	25.0 ± 1.2	0.04 ± 0.01
44	10	− 56.7 ± 2.1	27.5 ± 2.2	0.02 ± 0.01
24	8	− 47.1 ± 4.2	30.9 ± 2.3	0.01 ± 0.01
4	8	− 30.0 ± 5.0	34.6 ± 3.3	0.02 ± 0.01
F167L	134	36	− 70.3 ± 2.4	24.8 ± 0.6	0.08 ± 0.01*
44	5	− 57.6 ± 6.1	24.9 ± 1.6	0.02 ± 0.01
24	8	− 45.5 ± 3.0	30.8 ± 2.1	0.01 ± 0.01
4	7	− 26.2 ± 4.0	27.1 ± 1.4	< 0.01
A531V	134	10	− 59.6 ± 2.8*	29.4 ± 2.0	0.09 ± 0.02
4	9	− 16.4 ± 3.1*	60.0 ± 3.2*	0.08 ± 0.02*
G190S	134	15	+ 114.5 ± 4.5*	32.9 ± 1.3*	0.04 ± 0.01
4	9	+ 111.9 ± 11.6*	42.0 ± 2.0	0.02 ± 0.01
R105C	134	6	− 73.9 ± 6.4	21.1 ± 1.4	0.11 ± 0.03*
4	6	− 39.8 ± 7.1	35.3 ± 2.2	< 0.01
P558S	134	8	V1 = − 62.9 ± 2.2 V2 = + 100.5 ± 4.2	S1 = 17.0 ± 0.8 S2 = 32.9 ± 3.3	0.28 ± 0.02*
4	24	n.d.	n.d.	n.d.

The internal chloride concentration was modified by substituting glutamate for chloride ions. The external chloride concentration was maintained constant at 150 mM. The activation relationships obtained in each cell were fit with a Boltzmann equation (Eq. (1)) or a double Boltzmann equation for P558S (Eq. (2)), and fit parameters are reported as the mean ± SEM from N cells. V_0.5 is the half-maximum activation voltage, S is the slope factor, and Min is the minimal open probability. n.d. not determined.* indicates significant difference (at least P < 0.05) versus WT at the same internal chloride concentration, as calculated with unpaired Student's t test. Statistical analysis was not performed for V_0.5 and S values of P558S mutant. The mean relationships obtained from N cells are shown in Figs. 1D, 2D, and 6C.