Phosphorylation of the calcium antagonist receptor of the voltage-sensitive calcium channel by cAMP-dependent protein kinase.

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Abstract
Voltage-sensitive Ca channels are regulated by cAMP and protein phosphorylation. The Ca antagonist receptor of the voltage-sensitive Ca channel from transverse-tubule membranes [purified from rabbit fast muscle] consists of 3 subunits, designated .alpha., .beta. and .gamma.. The catalytic subunit of cAMP-dependent protein kinase phosphorylates both the .alpha. and .beta. subunits of the purified receptor at a rate and extent that suggests they are potential physiological substrates of this enzyme. The phosphorylation of the .alpha. and .beta. subunits in transverse-tubule membranes was analyzed by 2-dimensional gel electrophoresis. In intact transverse-tubule membranes, the .alpha. subunit is not significantly phosphorylated. The .beta. subunit, identified by its MW, pI and binding to wheat germ agglutinin-Sepharose, was 1 of the substrates selectively phosphorylated by cAMP-dependent protein kinase in transverse-tubule membranes. cAMP-dependent phosphorylation of the .beta. subunit of the Ca antagonist receptor may be an important regulatory mechanism for Ca channel function.