Identification and functional characterization of a calcium channel gamma subunit.

A positive selection technique was used to identify novel auxiliary calcium channel subunits that are similar to the skeletal muscle gamma subunit. A new rat gamma subunit cDNA was found, which was highly expressed in skeletal muscle tissue and was detected by RT-PCR in cardiac tissue. The 223-amino-acid-protein shares 84% and 79% identity, respectively, with the human and rabbit skeletal muscle subunits. Northern blot analysis revealed a single transcript of 1.5 kb in rat skeletal muscle, but not in cardiac tissue. Transient coexpression with the cardiac calcium channel complex demonstrated that the gamma subunit shifted the inactivation curve to negative potentials and accelerated current inactivation without changing other voltage-dependent properties of the channel.