Fig. 4.

Effects of polymers on the single-channel conductance of the CFTR Cl⁻ channel in the presence of AMP-PNP. a Relative changes in the unitary single-channel conductance as a function of the hydrodynamic radius of PEG molecules in the presence of AMP-PNP in the bath (intracellular) solution in the inside-out mode. Open diamonds represent the outward slope conductance obtained with polymers added to the pipette solution (configuration 4). Filled diamonds represent the inward slope conductance obtained with polymers added to the bath solution (configuration 5). Data were collected from 5–9 different patches for each polymer. *Significantly different from the slope conductance obtained in control conditions without polymers at P < 0.05. The slope conductances obtained in the presence of AMP-PNP for PEG 300, 400, 600 and 1,000 (filled diamonds) are significantly different from those in the absence of AMP-PNP (open triangles in Fig. 3a). Upper inset Schematic illustrations of configurations 4 and 5 used in this experiment. Lower inset Representative current traces recorded at +100 mV in the absence (upper trace) and presence (lower trace) of AMP-PNP in the bath (intracellular) solution. b Filling coefficients calculated according to Eq. 1 as a function of the hydrodynamic radius of PEG molecules. Symbols are the same as in (a). Solid lines are linear fits to the descending parts of the curves with correlation coefficient of −0.92 and −0.99 for extracellular and intracellular PEG application experiments, respectively. A horizontal dashed line corresponds to zero filling. R3 and R4 denote the radius of the extracellular and intracellular entrance, respectively, of the CFTR Cl⁻ channel in the presence of AMP-PNP in the bath solution