Functional Characterization of CaVα2δ Mutations Associated with Sudden Cardiac Death

L-type Ca 2+ channels play a critical role in cardiac rhythmicity. These ion channels are oligomeric complexes formed by the pore-forming Ca V α1 with the auxiliary Ca V β and Ca V α2δ subunits. Ca V α2δ increases the peak current density and improves the voltage-dependent activation gating of Ca V 1.2 channels without increasing the surface expression of the Ca V α1 subunit. The functional impact of genetic variants of CACNA2D1 (the gene encoding for Ca V α2δ), associated with shorter repolarization QT intervals (the time interval between the Q and the T waves on the cardiac electrocardiogram), was investigated after recombinant expression of the full complement of L-type Ca V 1.2 subunits in human embryonic kidney 293 cells. By performing side-by-side high resolution flow cytometry assays and whole-cell patch clamp recordings, we revealed that the surface density of the Ca V α2δ wild-type protein correlates with the peak current density. Furthermore, the cell surface density of Ca V α2δ mutants S755T, Q917H, and S956T was not significantly different from the cell surface density of the Ca V α2δ wild-type protein expressed under the same conditions. In contrast, the cell surface expression of Ca V α2δ D550Y, Ca V α2δ S709N, and the double mutant D550Y/Q917H was reduced, respectively, by ≈30–33% for the single mutants and by 60% for the latter. The cell surface density of D550Y/Q917H was more significantly impaired than protein stability, suggesting that surface trafficking of Ca V α2δ was disrupted by the double mutation. Co-expression with D550Y/Q917H significantly decreased Ca V 1.2 currents as compared with results obtained with Ca V α2δ wild type. It is concluded that D550Y/Q917H reduced inward Ca 2+ currents through a defect in the cell surface trafficking of Ca V α2δ. Altogether, our results provide novel insight in the molecular mechanism underlying the modulation of Ca V 1.2 currents by Ca V α2δ. Background: Missense mutations in Ca V α2δ1, an auxiliary subunit of cardiac L-type Ca V 1.2 channels, are associated with arrhythmias. Results: The reduction in the cell surface density of Ca V α2δ1 D550Y/Q917H was sufficient to impair Ca V 1.2 currents. Conclusion: Defects in the cell surface trafficking of Ca V α2δ1 mutants down-regulate L-type currents. Significance: CACNA2D1 genetic variants may trigger arrhythmias by reducing L-type Ca 2+ currents.