Effects of Ba²⁺ and Na⁺ ion as charge carrier on VDI of Ca_V1.2 current expressed in tsA-201 cells. (A) Relationship between r₁₀₀₀ and current amplitude of Ca_V1.2 currents (n = 52) with Ba as charge carrier I_CaV1.2(Ba). The straight line represents a linear regression (r = −0.61; P < 0.001). (B) Inactivation of typical current traces from cells with low and high current amplitudes (cells a and b from A). (C) Relationship between r₁₀₀₀ and current amplitude of Ca_V1.2 currents (n = 19) with Na⁺ as charge carrier I_CaV1.2(Na). The straight line represents a linear regression (r = −0.11; P = NS). (D) Inactivation of typical current traces from cells with low and high current amplitudes (cells a and b from C). Currents were elicited by a depolarization to 0 mV for 1,000 ms from a HP of −80 mV and normalized to their peak amplitudes. The Mg_i concentration was 0.8 mM. Dotted lines in this and all figures represent the zero current level.