Identification of a cardiac isoform of the murine calcium channel α1C (Ca_v1.2-a) subunit and its preferential binding with the β2 subunit

We describe a cardiac muscle isoform of the voltage-dependent calcium channel α1 subunit, which corresponds to the rabbit ortholog of α1C-a (Ca_v1.2a). We also cloned smooth muscle isoforms α1C-b (Ca_v1.2b) and α1C-d (Ca_v1.2d). Differences among these three isoforms lie within the N-terminal region (exon 1A or 1B), the sixth transmembrane segment of domain I (exon 8A or 8B), and the use of exon 10, which forms the intracellular loop between transmembrane domains I and II. Two-hybrid analysis revealed interactions among the three α1 isoforms and β subunits. In vitro overlay and immunoprecipitation analyses revealed preferential binding between α1C-a and β2, which is also expressed at a high level in the heart.