Figure 5. Ca_V1.2 CDI Requires a Negative Charge at the DII, DIII, or DIV SF (+1) Position.

(A) Exemplar normalized recordings at +20 mV in Ca²⁺ (black) or Ba²⁺ (gray) from Xenopus oocytes expressing the Ca_V1.2 or the indicated mutants.

(B) Fractional current remaining 300 ms post-depolarization (R₃₀₀) as a function of the membrane potential for channels in (A). Data in (A) and (B) are identical to Figures 1A and 1B.

(C) Exemplar normalized recordings at +20 mV in Ca²⁺ (blue) or Ba²⁺ (orange) from Xenopus oocytes expressing the indicated Ca_V1.2 mutants moving the negative charge at the (+1) position of the selectivity filter from domain II to domains I, III, or IV. Ca²⁺ (black) and Ba²⁺ (gray) currents from Ca_V1.2 are shown for comparison.

(D) Fractional current remaining 300 ms post-depolarization (R₃₀₀) as a function of the membrane potential for channels in (C).

(E) Average f values at 20 mV. **p < 0.001 compared to the corresponding single mutant.

(F) Dose-response curves for Ca²⁺ block of Li⁺ currents for Ca_V1.2, DI_Asp G364D/D707G (blue triangles), DIII_Asp D707G/G1116D (inverted blue triangles), and DIV_Asp D707A/A1417D (lavender diamonds). Each data point at each Ca²⁺ concentration is normalized to the current at 3 nM Ca²⁺ and averaged for n = 7–9 oocytes.