Phosphorylation and dephosphorylation of dihydropyridine-sensitive voltage-dependent Ca2+ channel in skeletal muscle membranes by cAMP- and Ca2+-dependent processes.

The phosphorylation and dephosphorylation of the dihydropyridine-sensitive Ca2+ channel was studied in transverse-tubule membranes isolated from rabbit skeletal muscle. Exposure of these membranes to either the cAMP-dependent protein kinase or a Ca2+/calmodulin-dependent protein kinase resulted in a rapid phosphorylation of a protein with properties similar to the major component of the skeletal muscle Ca2+ channel. The molecular mass of the phosphoprotein was 140 or 160 kDa, depending on the electrophoretic conditions. The stoichiometry of the phosphorylation was calculated to be 0.4-1.0 mol of phosphate per mol of protein. Neither the rate nor the extent of phosphorylation was affected by dihydropyridines. Limited proteolytic digestion of the protein that had been phosphorylated by either or both protein kinases yielded a single phosphopeptide of approximately equal to 5.4 kDa. The Ca2+-dependent phosphatase calcineurin dephosphorylated the membrane-bound Ca2+ channel that had been previously phosphorylated by either protein kinase. The results suggest that the major component of the dihydropyridine-sensitive Ca2+ channel from skeletal muscle can be effectively phosphorylated and dephosphorylated in its native state by cAMP- and Ca2+-dependent processes.