Purified L-type calcium channels: only one single polypeptide (alpha 1-subunit) carries the drug receptor domains and is regulated by protein kinases.

The L-type calcium channel was purified from guinea-pig skeletal muscle T-tubule membranes. The purified preparation retained the binding activity for 1,4 dihydropyridines, phenylalkylamines and d-cis diltiazem. Four polypeptides with apparent molecular masses of 180-190, 150-155, 55-60 and 28-35 kDa (termed alpha 1, alpha 2, beta and gamma subunit) copurified with reversible drug binding. In photoaffinity labeling experiments only the alpha 1 subunit was shown to carry the drug receptors. Phosphorylation and functional reconstitution experiments revealed that the cAMP dependent phosphorylation of the alpha 1 subunit is responsible for calcium channel regulation.