γ1-Dependent Down-regulation of Recombinant Voltage-gated Ca2+ Channels

(1) Voltage-gated Ca2+ (CaV) channels are multi-subunit membrane complexes that allow depolarization-induced Ca2+ influx into cells. The skeletal muscle L-type CaV channels consist of an ion-conducting CaV1.1 subunit and auxiliary α2δ−1, β1 and γ1 subunits. This complex serves both as a CaV channel and as a voltage sensor for excitation–contraction coupling. (2) Though much is known about the mechanisms by which the α2δ−1 and β1 subunits regulate CaV channel function, there is far less information on the γ1 subunit. Previously, we characterized the interaction of γ1 with the other components of the skeletal CaV channel complex, and showed that heterologous expression of this auxiliary subunit decreases Ca2+ current density in myotubes from γ1 null mice. (3) In the current report, using Western blotting we show that the expression of the CaV1.1 protein is significantly lower when it is heterologously co-expressed with γ1. Consistent with this, patch-clamp recordings showed that transient transfection of γ1 drastically inhibited macroscopic currents through recombinant N-type (CaV2.2/α2δ−1/β3) channels expressed in HEK-293 cells. (4) These findings provide evidence that co-expression of the auxiliary γ1 subunit results in a decreased expression of the ion-conducting subunit, which may help to explain the reduction in Ca2+ current density following γ1 transfection.