Voltage and [K⁺]_ext dependence of stationary currents in the absence of Na⁺_ext. (A and B) I-V curves of normalized K⁺-dependent ^NMDGI_xK difference currents of the ΔYY construct (A) and ATP1A2 WT (B) in the absence of extracellular Na⁺ ([NMDG⁺]_ext = 100 mM, pH 7.4) with [K⁺]_ext as indicated. Also shown in A and B are the ouabain-sensitive currents (^NMDGI_ouab) in the absence of K⁺ for the ΔYY construct and ATP1A2 WT. (C) K_0.5(K⁺_ext) values for the ΔYY construct and for ATP1A2 WT at [Na⁺]_ext = 0. For each construct, data are means ± SD from eight oocytes out of two batches.