Functional characterization of CaV {alpha}2{delta} mutations associated with sudden cardiac death [Membrane Biology]

December 19th, 2014 by Bourdin, B., Shakeri, B., Tetreault, M.–P., Sauve, R., Lesage, S., Parent, L.

L-type Ca2+ channels play a critical role in cardiac rhythmicity. These ion channels are oligomeric complexes formed by the pore-forming CaVα1 with the auxiliary CaVβ and CaVα2δ subunits. CaVα2δ subunit increases the peak current density and improves the voltage-dependent activation gating of CaV1.2 channels without increasing the surface expression of the CaVα1 subunit. The functional impact of genetic variants of CACNA2D1 (the gene encoding for CaVα2δ), associated with shorter repolarization QT intervals, was investigated after recombinant expression of the full complement of L-type CaV1.2 subunits in HEKT 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 CaVα2δ wild-type protein correlates with the peak current density.Furthermore, the cell surface density of CaVα2δ mutants S755T, Q917H, and S956T was not significantly different than the cell surface density of the CaVα2δ wild-type protein expressed under the same conditions. In contrast, the cell surface expression of CaVα2δ D550Y, CaVα2δ 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 CaVα2δ was disrupted by the double mutation. Co-expression with D550Y/Q917H significantly decreased CaV1.2 currents as compared with results obtained with CaVα2δ wild-type. It is concluded that D550Y/Q917H reduced inward Ca2+ currents though a defect in the cell surface trafficking of CaVα2δ. Altogether, our results provide novel insight in the molecular mechanism underlying the modulation of CaV1.2 currents by CaVα2δ.