The alpha 1 and alpha 2 polypeptides of the dihydropyridine-sensitive calcium channel differ in developmental expression and tissue distribution

Abstract

The dihydropyridine (DHP) binding complex isolated from skeletal muscle contains two large proteins, alpha 1 and alpha 2, and at least two smaller polypeptides. The alpha 1 subunit has a primary structure expected for ion channels and is a functional component of a DHP-sensitive, voltage-activated calcium channel. The functions of the alpha 2 protein and the smaller polypeptides are unknown. We prepared monoclonal antibodies to the alpha 1 and alpha 2 polypeptides and studied the developmental appearance and tissue distribution of these two proteins. In rat skeletal muscle, the levels of alpha 1 are quite low during the first 10 days after birth, then rise dramatically, and, by day 20, approach those found in adult muscle. In direct contrast, alpha 2 is present in substantial amounts in rat muscle at birth and increases only slightly during this same period of development. Furthermore, alpha 1 is detected only in skeletal muscle, whereas alpha 2 is present in a variety of tissues. These results provide evidence for the segregation of these two polypeptides and suggest that the function of alpha 2 is not limited to that associated with the DHP-sensitive calcium channel.