Table I

Comparison of the Permeability of Wild-Type and TT338,339AA Channels to Some Extracellular Anions

Extracellular anionWild-Type CFTRTT338,339AAIon dimensions
ErevPX/PClnErevPX/PCln
mVmVÅ
Chloride0 1.00801.0083.62 × 3.62 × 3.63
Iodide−18.1 ± 0.12.02−37.7 ± 1.04.42 ± 0.0834.32 × 4.32 × 4.32
Bromide −5.2 ± 1.01.22 ± 0.054−11.5 ± 0.71.57 ± 0.743.90 × 3.90 × 3.90
FluorideNo reversal<0.063No reversal<0.0632.72 × 2.72 × 2.72
Nitrate −8.2 ± 2.11.43 ± 0.104−23.6 ± 0.22.53 ± 0.0243.10 × 4.76 × 5.17
Formate+43.4 ± 3.70.18 ± 0.104+22.5 ± 1.00.42 ± 0.0253.40 × 4.62 × 4.82
Bicarbonate+49.6 ± 1.80.14 ± 0.02803.40 × 4.95 × 5.96
Acetate+61.1 ± 0.20.09 ± 0.002+50.6 ± 0.20.14 ± 0.0043.99 × 5.18 × 5.47
PropanoateNo reversal<0.065+53.2 ± 1.00.12 ± 0.0054.12 × 5.23 × 7.05
PyruvateNo reversal<0.065+32.7 ± 0.50.28 ± 0.0154.09 × 5.73 × 6.82
Methane sulfonateNo reversal<0.066No reversal<0.0655.08 × 5.43 × 5.54
Ethane sulfonateNo reversal<0.065No reversal<0.0634.94 × 5.37 × 7.44
GluconateNo reversal<0.065No reversal<0.0644.91 × 6.86 × 12.09
ATP07.65 × 9.23 × 18.71
ATP4−7.30 × 9.43 × 18.40
  • Summary of mean reversal potentials (Erev) measured with different extracellular anions in wild-type CFTR and TT338,339AA channels. Relative permeabilities (PX/PCl) were calculated from the reversal potentials using Eq. 1 (see methods). n represents the number of experiments with each ion. Wild-type values for Br, I, and F are from the preceding paper (Tabcharani et al., 1997). Also shown are the minimal unhydrated dimensions of the ions used, which were estimated using Molecular Modeling Pro computer software (WindowChem Software Inc., Fairfield, CA). The estimated minimal dimensions of ATP, both in the fully protonated (ATP0) and fully ionized (ATP4−) forms, are also shown for comparison. Nonhalide ions are shown in the order of their unhydrated diameters, estimated as described in the text.