Mg_i modulation of VDI of L-type calcium current from mouse ventricular myocytes. (A) Comparison of VDI with Ca²⁺ versus Na⁺ as charge carrier. Normalized and averaged current traces for Ca²⁺ I_Ca,L(Ca) (n = 6) and Na⁺ I_Ca,L(Na) (n = 9). (B) Effect of Mg_i on the inactivation of I_Ca,L(Na). Normalized average current traces are shown. (C) Plot of r₃₀₀ versus Mg_i concentrations. n = 4, 9, 13, and 10 for 0.26, 0.8, 2.4, and 7.2 mM Mg_i, respectively.