Molecular Properties of the Voltage-Sensitive Calcium Channel

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Abstract
Skeletal muscle T-tubules are particularly rich in receptors for Ca2+ channel blockers such as 1,4-dihydropyridines (DHP), verapamil-like molecules, bepridil, and diltiazem. These receptors have been biochemically identified using tritiated ligands, and their affinities for corresponding drugs have been measured. The DHP receptor has been purified from skeletal muscle. It is a protein of 170,000 Md comprising a large polypeptide of 142,000 Mr and a smaller peptide of 32–33,000 Mr. The two polypeptides are linked by disulfide bridges. Affinity labeling experiments with bepridil, diltiazem, and DHP indicate that the 142,000 Mr polypeptide contains receptors for the different drugs. Polyclonal and monoclonal antibodies have been prepared against the Ca2+ channel protein. They have confirmed the subunit structure identified by purification and they have shown that the same arrangement of polypeptides is present in Ca2+ channel proteins from heart and smooth muscle membranes. The cAMP-dependent phosphorylation that activates the slow. Ca2+ channel occurs on the 142,000 Mr protein.

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