Figure 6.

Cation versus anion selectivity of human, baboon, and chimeric APOL1. A, planar lipid bilayer setup. B, a conductance was obtained with APOL1 variants or chimeras as described in the legend to Fig. 4. The cis side was then perfused with pH 5.6 buffer and then adjusted to pH 7.2 with KOH. The reversal potential (the voltage at which the current registered zero, E_rev) was then determined before and after successive additions of 50 μl of 3 m KCl to the cis side. B and C, plotted are average E_rev from N independent experiments ± S.D. (error bars) versus the cis/trans K⁺ activity gradient (αK⁺_cis/αK⁺_trans, K⁺ activity was taken as equal to KCl activity; see “Materials and methods”). In some cases, error bars are smaller than the data points. In all cases, electrode offsets were <1 mV. The ideal potassium-selective line is defined by the Nernst potential (E_rev = 59 × log₁₀[αK⁺_cis/αK⁺_trans]).