Figure 1.

Effect of Mg_i on Ca_V1.2 channels. (A) Typical current traces from cells exposed to the indicated concentrations of Mg_i. Ba²⁺ currents were elicited by a depolarization to +40 mV. (B) Effect of Mg_i on normalized tail current amplitudes (mean I_tail/mean I_tail [0.26 mM Mg_i]). Under voltage clamp conditions, Ba²⁺ currents were elicited by a 20-ms depolarization from a holding potential of −80 mV to potentials from −40 to 80 mV in 5-mV increments followed by a step repolarization to −40 mV to elicit tail currents. The bracket labeled WT Range indicates the change in normalized tail current amplitude for a change from 0.26 mM to 7.2 mM Mg_i. (C) Effect of Mg_i on the voltage dependence of activation of Ca_V1.2 channels. Tail current amplitudes were normalized to the maximum value at positive test potential. (D) Effect of Mg_i on the voltage dependence of inactivation of Ca_V1.2 channels. Under voltage clamp conditions, tsA-201 cells were depolarized from a holding potential of −80 mV for 4 s to membrane potentials from −80 to 20 mV in 10-mV increments. Ba²⁺ currents were then elicited by depolarization to 30 mV for 30 ms, followed by repolarization to −40 mV to measure tail currents.