Functional roles of the gamma subunit of the skeletal muscle DHP-receptor

From α1s splicing to γ1 function: A new twist in subunit modulation of the skeletal muscle L-type Ca2+ channel

Melzer discusses a recent JGP study showing that alternative splicing of the skeletal muscle L-type calcium channel impacts on a modulatory effect of its γ subunit.

gamma1-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 alpha2delta-1, beta1 and gamma1 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 alpha2delta-1 and beta1 subunits regulate CaV channel function, there is far less information on the gamma1 subunit. Previously, we characterized the interaction of gamma1 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 gamma1 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 gamma1. Consistent with this, patch-clamp recordings showed that transient transfection of gamma1 drastically inhibited macroscopic currents through recombinant N-type (CaV2.2/alpha2delta-1/beta3) channels expressed in HEK-293 cells. (4) These findings provide evidence that co-expression of the auxiliary gamma1 subunit results in a decreased expression of the ion-conducting subunit, which may help to explain the reduction in Ca2+ current density following gamma1 transfection.