Effects of Ca²⁺ substitution by Mg²⁺ or ionic block by La³⁺ on Ca_v2.3 channel voltage dependence. (A) Isochronous activation curves constructed from Ca_v2.3 channel currents before (black squares), during (blue circles), and after (gray squares) substitution of 4 mM free Ca²⁺ as the charge carrier by 4 mM free Mg²⁺ (n = 5 cells). (B) Isochronous activation curves constructed from Ca_v2.3 channel currents carried by 4 mM free Ca²⁺ before (black squares), during (red circles), and after (gray squares) application of 100 µM free La³⁺ (n = 6 cells).