FIGURE 2.

Effects of E374 mutations on Mg²⁺ sensitivity. (A and B) Mg²⁺-dependent activation of E374A (A) and E374D (B) channels at 0 [Ca²⁺]_i. (Left panels) Current traces recorded at 0 (upper) or 10 mM (lower) [Mg²⁺]_i. Testing potentials were from −30 to 250 mV with 20-mV increments. The holding and repolarizing potentials were −80 and −50 mV, respectively. (Right panels) Mean G-V relations. Gray lines are G-V relations of WT mSlo1 channels for comparison. G-V relations of mutant channels are fitted with the Boltzmann relation (solid lines; see Materials and Methods). (C) G-V shift from 0 to 10 mM [Mg²⁺]_i at 0 [Ca²⁺]_i of WT mSlo1 and mutant channels. V_½ is the voltage where the G-V relation is half-maximum. Gray bars are the data measured in experiments, and black bars are the experimental data subtracted by the amount of G-V shift (−12.2 mV) caused by Mg²⁺ binding to the low-affinity Mg²⁺ site and calculated from model simulation (see Materials and Methods).