FUNCTION OF A TRUNCATED DIHYDROPYRIDINE RECEPTOR AS BOTH VOLTAGE SENSOR AND CALCIUM-CHANNEL

THE skeletal muscle dihydropyridine (DHP) receptor serves dual functions, as a voltage sensor for excitation-contraction coupling and as an L-type calcium channel1-3. Biochemical analysis indicates the presence of two forms of the DHP receptor polypeptide in skeletal muscle, a full-length translation product present as a minor species and a much more abundant form that has a truncated carboxy-terminus4-6. On the basis of these and other observations7, it has been proposed8 that, in skeletal muscle, only the full-length DHP receptor can function as a calcium channel and that the truncated form can only function as a voltage sensor for excitation-contraction coupling. To resolve this issue, we have now constructed a complementary DNA (pC6DELTA1) encoding a protein corresponding to the truncated DHP receptor in skeletal muscle. Expression of pC6DELTA1 in dysgenic myotubes fully restores both excitation-contraction coupling and calcium current, consistent with the idea that a single class of DHP receptors performs both functions.