γ₁-dependent down-regulation of recombinant voltage-gated Ca²⁺ channels

(1) Voltage-gated Ca²⁺ (Ca_V) channels are multi-subunit membrane complexes that allow depolarization-induced Ca ²⁺ influx into cells. The skeletal muscle L-type Ca_V channels consist of an ion-conducting Ca_V1.1 subunit and auxiliary α₂δ-1, β₁ and γ₁ subunits. This complex serves both as a Ca_V 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 Ca_V 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 Ca_V 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 Ca_V1.1 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 (Ca_V2.2/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.