CYCLIC-AMP-DEPENDENT PROTEIN-KINASE PHOSPHORYLATES RESIDUES IN THE C-TERMINAL DOMAIN OF THE CARDIAC L-TYPE CALCIUM-CHANNEL ALPHA(1) SUBUNIT

The molecular basis of the regulation of cardiac L-type calcium channe l activity by cAMP-dependent protein kinase (cA-PK) remains unclear. D irect cA-PK-dependent phosphorylation of the bovine ventricular alpha( 1) subunit in vitro has been demonstrated in microsomal membranes, det ergent extracts and partially purified (+)-[H-3]PN 200-110 receptor pr eparations. Two P-32-labelled phosphopeptides, derived from cyanogen b romide cleavage, of 4.7 and 9.5 kDa were immunoprecipitated specifical ly by site-directed antibodies against the rabbit cardiac alpha(1) sub unit amino acid sequences 1602-1616 and 1681-1694, respectively, consi stent with phosphorylation at the cA-PK consensus sites at Ser(1627) a nd Ser(1700). No phosphopeptide products consistent with phosphorylati on at three other C-terminal cA-PK consensus phosphorylation sites (Se r(1575), Ser(1848) and Ser(1928)) were identified using similar proced ures suggesting that these sites are poor substrates for this kinase. Ser(1627) and Ser(1700) may represent sites of cA-PK phosphorylation i nvolved in the physiological regulation of cardiac L-type calcium chan nel function.