Li ⁺ selectivity evaluation in NavAb N49K/T206A, S178T ^NK/TA , S178A ^NK/TA , and S178G ^NK/TA mutants. (A) Whole-cell currents in NavAb N49K when a pulse of −20 mV from a −140 mV holding potential was given for 100 ms. (B) Current–voltage relationship of each construct with 150 mM [Na⁺]_out and 150 mM [Na⁺]_in. Background (BG) indicates NavAb N49K/T206A mutant without the Ser178 mutation. Cyan represents BG, and magenta, green, and yellow represent S178T, S178A, and S178G mutants with the BG mutation, respectively. The correspondence between these colors and constructs is the same in C and D. (C) Representative current traces of BG and each Ser178 mutant were obtained using the ramp protocol. The reversal potentials recorded with three different ramp pulses were averaged and used. Currents were measured at 150 mM [Li⁺]_out and 150 mM [Na⁺]_in. (D) Current–voltage relationship plots of BG and each Ser178 mutant generated by the ramp pulses in 150 mM [Li⁺]_out and 150 mM [Na⁺]_in. (E) The relative permeability of Li⁺ to Na⁺ in BG and each Ser178 mutant, calculated from the reversal potentials shown in C. Statistical analyses for Li⁺ selectivity among BG and each Ser178 mutant were performed by Dunnett’s multiple comparison test. P values <0.05, <0.01, and no significant differences are indicated by “*,” “**,” and “NS,” respectively.