Distinct functional signature of Ca _V 1.3 VDI. (A and B) Exemplar Ba²⁺ current traces evoked in response to a family of voltage-steps show VDI of both wild-type Ca_V1.3 (panel A) and DIV W[+2]A mutant (panel B). CaM₁₂₃₄ coexpressed to exclude the potential contribution of CDI. (C) A two-pulse protocol is used to quantify the voltage dependence of inactivation. Comparison of Ba²⁺ currents for wild-type Ca_V1.3 during the prepulse versus the postpulse. Ca_V1.3 currents are increased in response to higher test-pulse potentials. See Fig. S2 B for full exemplar trace. (D) DIV W[+2]A mutant channels exhibit diminished peak currents during the postpulse following test pulse to intermediate voltages. See Fig. S2 C for a full exemplar trace. (E) Analysis of wild-type Ca_V1.3 reveals minimal VDI across multiple voltages. For each dot and error, mean ± SEM n = 7. (F) VDI of DIV W[+2]A mutation exhibits a U-shaped voltage-dependence with the strongest inactivation observed near 0 mV. Blue curve, voltage-dependence of inactivation obtained from the whole cell normalized IV relations (Fig. S2 E). For each dot and error, mean ± SEM n = 7 cells. (G) Exemplar traces show similar kinetics of inactivation for DIV W[+2]A mutant in the presence of various β subunits. (H) Population data confirms minor differences in VDI quantified as r₈₀₀ measured at 0 mV in the presence of various β subunits. Each bar and error, mean ± SEM. n = 6 cells (β_1B), n = 8 cells (β_2A), n = 5 cells (β₃), n = 7 cells (β₄). P = 0.076 by one-way ANOVA.