Fig. 2.

Four mutant types recovered from yeast selection restore K⁺ selectivity. (A) S177W mutant channels but not S177T or the four S177W-containing mutant types sustained Na⁺ currents (at –100 mV). Current traces were elicited with voltage pulses from +40 to –150 mV (in 10-mV increments) from a holding potential of 0 mV in 90 mM K (solid line), 90 mM Na (long-dash line), and 90 mM NMDG (short-dash line). (B) S177W but not S177T or the S177W-containing mutant types displayed significant Na⁺ permeability, as indicated by current (I_Na/I_K) and permeability (P_Na/P_K) ratios deduced from the difference in reversal potential (E_rev) measured in 90 mM Na and 90 mM K solutions.