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 Ca2+ influx into cells. The skeletal muscle L-type Ca-V channels consist of an ion-conducting Ca(V)1.1 subunit and auxiliary alpha(2)delta-1, beta(1) and gamma(1) 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 alpha(2)delta-1 and beta(1) subunits regulate Ca-V channel function, there is far less information on the gamma(1) subunit. Previously, we characterized the interaction of gamma(1) 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 gamma(1) null mice. (3) In the current report, using Western blotting we show that the expression of the Ca(V)1.1 protein is significantly lower when it is heterologously co-expressed with gamma(1). Consistent with this, patch-clamp recordings showed that transient transfection of gamma(1) drastically inhibited macroscopic currents through recombinant N-type (Ca(V)2.2/alpha(2)delta-1/beta(3)) channels expressed in HEK-293 cells. (4) These findings provide evidence that co-expression of the auxiliary gamma(1) subunit results in a decreased expression of the ion-conducting subunit, which may help to explain the reduction in Ca2+ current density following gamma(1) transfection.