Figure 1.

Selectivity of macroscopic CFTR currents. (A) Example I-V curves recorded with NaCl in the extracellular (pipette) solution and NaCl, NaSCN, NaClO₄, Na · gluconate (Gluc) or NaPF₆ (hexafluorophosphate) in the intracellular (bath) solution. (B) Example I-V curves with NaCl in the intracellular solution and NaCl, NaSCN, NaClO₄, or Na · gluconate in the extracellular solution. (C and D) Apparent permeability ratios for different intracellular (C) or extracellular (D) ions (P _X/P _Cl; taken from Table I) as a function of mean unhydrated ionic diameter. Open symbols represent lyotropic (weakly hydrated) ions (from left to right: SCN⁻, Cl⁻, NO₃ ⁻, Br⁻, I⁻, ClO₄ ⁻, benzoate, PF₆ ⁻), and filled circles represent kosmotropic (strongly hydrated) ions (from left to right: fluoride, formate, acetate, propanoate, pyruvate, methane sulfonate, glutamate, isethionate, gluconate, glucoheptonate, glucuronate, MES, ga- lacturonate, HEPES, TES, lactobionate) (see Collins, 1997). Ions that were not measurably permeant are shown as diamonds on the abscissa for display purposes only. In each case, the data have been fitted by Eq. 2 (see methods), giving estimates of the functional pore diameter of 5.3 (C, ○), 13.8 (C, •), 4.9 (D, ○) and 5.3 (D, •) Å.