Figure 5.

Mg²⁺ competes with Ca²⁺ by binding to Ca²⁺ binding sites. (A) Current traces of WT mslo1 channels (left) and E374A:E399N mutant channels (right) recorded at indicated [Mg²⁺]_i and [Ca²⁺]_i. Testing potentials were −140 to 180 mV with 20-mV increments. The holding and repolarizing potential were −80 and −50 mV, respectively. (B) Mean G-V relations of WT mslo1 (gray symbols) and the mutant channels (black symbols) at 0 or 10 mM [Mg²⁺]_i and 3.7 μM [Ca²⁺]_i, and fits with the Boltzmann relation (solid lines). (C) G-V shifts from 0 to 10 mM [Mg²⁺]_i at 3.7 μM [Ca²⁺]_i of WT mslo1 and the mutant channels.