Mg_i dependence of L-type Ca²⁺ current density in mouse ventricular myocytes with Ca²⁺ and Na⁺ as charge carriers. (A) Effect of Mg_i on I_Ca,L(Ca) density. Currents were elicited by 300-ms depolarizations from an HP of −50 mV to the indicated potentials from −50 to 70 mV. (B) Mean peak I_Ca,L(Ca) density with different Mg_i concentrations. n = 13, 8, and 11 myocytes for 0.8, 2.4, and 7.2 mM Mg_i, respectively. (C) Effect of Mg_i on I_Ca,L(Na) density. (D) Mean peak I_Ca,L(Na) density measured at different Mg_i concentrations. n = 7, 6, and 6 myocytes for 0.8, 2.4, and 7.2 mM Mg_i, respectively. Error bars are ± SEM in this and all subsequent figures. In this and all figures, * and ** indicate P < 0.05 and P < 0.01, respectively.