Figure 4.
Figure 4. Charge additions at the inner cavity of Shaker K channels. (Left) Leak- and capacitance-subtracted single-channel traces of (A) Shaker-A471D, (B) P475D/A471D, and (C) P475D/S479D/A471D in the 30-1,000-mM range of symmetrical [K+]. (Right) I-V relations obtained from open-channel amplitudes. The continuous traces are third-degree polynomial functions fitted to the data. The slope of the fit function at zero voltage was used to obtain the conductance values. (D) Slope conductance of open-channel amplitude displayed in A–C is plotted vs. [K+]. Data were fitted to a Langmuir isotherm with the following fitting parameters: A471D, Kd = 67 ± 1.4 mM and gmax = 96 ± 2 pS; P475D/A471D, Kd = 65 ± 12 mM and gmax = 175 ± 4 pS; P475D/S479D/A471D, Kd = 6.7 ± 3.3 mM and gmax = 185 ± 6 pS.

Charge additions at the inner cavity of Shaker K channels. (Left) Leak- and capacitance-subtracted single-channel traces of (A) Shaker-A471D, (B) P475D/A471D, and (C) P475D/S479D/A471D in the 30-1,000-mM range of symmetrical [K+]. (Right) I-V relations obtained from open-channel amplitudes. The continuous traces are third-degree polynomial functions fitted to the data. The slope of the fit function at zero voltage was used to obtain the conductance values. (D) Slope conductance of open-channel amplitude displayed in A–C is plotted vs. [K+]. Data were fitted to a Langmuir isotherm with the following fitting parameters: A471D, Kd = 67 ± 1.4 mM and gmax = 96 ± 2 pS; P475D/A471D, Kd = 65 ± 12 mM and gmax = 175 ± 4 pS; P475D/S479D/A471D, Kd = 6.7 ± 3.3 mM and gmax = 185 ± 6 pS.

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