Shifts of the Kv3.1 reversal potential in different mixtures of K⁺_i/o and NMDG⁺ _i/o. (A–C; Top) Currents recorded in the presence of symmetrical 140 mM NMDG⁺_i/o (A and B) or 40 mM NMDG⁺_i and 110 mM NMDG⁺_o (C) plus the concentration ratios for K⁺ indicated above the traces in A–C. The pulse protocol used for the experiments is similar to that shown in Fig. 7 A. The internal solutions were Mg²⁺ free in all experiments. (A–C; bottom) Peak tail current–voltage curves showing the shift in reversal potential in mixtures of K⁺ and NMDG⁺. The reversal potentials were −12.3 (−14.4 ± 0.8 mV; n = 7), −20.6 (−20.6 ± 1.2 mV; n = 6), and −28.8 mV (−28.0 ± 2.0 mV; n = 11) for A, B, and C, respectively. The differences between A, B, and C are all highly significant (P < 0.001).