Voltage and [K⁺]_ext dependence of stationary currents at [Na⁺]_ext = 100 mM. (A) I-V curves of normalized ouabain-sensitive K⁺-dependent currents ^NaI_xK(ouab) of the Na⁺/K⁺-ATPase ΔYY deletion construct measured at 100 mM [Na⁺]_ext and [K⁺]_ext as indicated. (B) I-V curves of normalized K⁺-induced difference currents ^NaI_xK (at 100 mM [Na⁺]_ext) of the ΔYY construct. (C) Voltage-dependent ^NaK_0.5(K⁺_ext) values of the ΔYY construct from fits of a Hill function to the ^NaI_xK currents in B at each membrane potential. The minimal ^NaK_0.5(K⁺_ext) was 1.02 ± 0.06 mM at −80 mV. The dashed line delineates the corresponding WT data from E for comparison. (D) I-V curves of normalized ^NaI_xK difference currents for ATP1A2 WT with [K⁺]_ext as indicated. (E) Voltage-dependent ^NaK_0.5(K⁺_ext) values for ATP1A2 WT from fits of a Hill function to the ^NaI_xK currents in D at each membrane potential. The minimal ^NaK_0.5(K⁺_ext) was 1.10 ± 0.05 mM at 0 mV. Data for both WT and ΔYY are means ± SE from 14 cells of three oocyte batches. (F) I-V curves of normalized ^NaI_10K(ouab) and ^NaI_0K(ouab) currents of ATP1A2 WT and the ΔYY construct at pH_ext 7.4 ([Na⁺]_ext = 100 mM). Data are means ± SE from six (WT) and seven (ΔYY) cells from two batches.