Figure 4.

S460G:A463C:T469V and A463C are both selective for K⁺ in physiological conditions. Representative current traces from S460G:A463C:T469V (A) and A463C (B) elicited by a depolarizing step from a holding potential of −100 to +50 mV and followed by hyperpolarizing steps ranging from −30 to −160 mV in 10-mV decrements. The external solution (A and B) contained (mM): 140 NaCl, 2 KCl, 4 MgCl₂, 2 CaCl₂, 5 HEPES, pH 7.1. The internal solution contained (mM): 140 KCl, 2 MgCl₂, 10 EGTA, 10 HEPES, pH 7.2. (C) Instantaneous current–voltage relationship as measured isochronally from the tail current family shown in A. The predicted Nernst reversal potential for K⁺ under these ionic conditions is −110 mV. The measured reversal potential is −112 ± 4 mV (n = 4). (D) Instantaneous current–voltage relationship as measured from the current family shown in B. The predicted Nernst reversal potential for K⁺ under these ionic conditions is −110 mV. The measured reversal potential is −106 ± 9 mV (n = 4).