Fig. 3.

Effects of divalent ions on inactivation in MthK. (A) Representative currents with 100 μM Mg²⁺, Ca²⁺, and Sr²⁺ over a range of voltages. Ca²⁺ and Sr²⁺ facilitate entry to an inactivated state at depolarized voltages. (B) Po vs. voltage in the presence of Mg²⁺, Ca²⁺, or Sr²⁺ at the indicated concentrations; curves represent fits with a Boltzmann equation. Increasing [Mg²⁺] has nominal effects on Po compared with increasing [Ca²⁺] or [Sr²⁺], consistent with the idea that Ca²⁺ and Sr²⁺ enhance entry to an inactivated state by acting at a site that is inaccessible to Mg²⁺.