Figure 6

Elimination of the extremely slow component of Mg²⁺ unblock in E224Q mutant channel by concomitant specific mutations at M183 and A178.

(a) Sample sweeps of the extremely slow tail currents in the E224Q mutant channel in symmetrical 100 mM K⁺ (see Fig. 3c for the pulse protocol). The slow tails are considerably slower than that in the E224G mutant channel. Also, much higher concentrations of Mg²⁺ are required for the emergence of slow tails. In addition, the extremely slow tails signaling Mg²⁺ unblocking in the E224Q single mutant channel are evidently accelerated in specific double–mutant (e.g., E224Q/M183W, E224Q/M183N and E224Q/A178C) channels. The dashed lines indicate the zero current level. (b) Cumulative results were obtained for the E224Q, E224Q/M183W, E224Q/M183N and E224Q/A178C double mutant channels (each n = 5). tau _{on, 1} and tau _{on, 2} denote the time constant of the growing course of the slow tails (at −100 mV) and the time constant of the decay of the macroscopic outward currents (at +100 mV) in 3 mM Mg²⁺ from the experiments in part a respectively (the same approach as that shown in Fig. 3c).