CAMP-DEPENDENT PHOSPHORYLATION SITES AND MACROSCOPIC ACTIVITY OF RECOMBINANT CARDIAC L-TYPE CALCIUM CHANNELS

The involvement of cAMP-dependent phosphorylation sites in establishin g the basal activity of cardiac L-type Ca2+ channels was studied in HE K 293 cells transiently cotransfected with mutants of the human cardia c a, and accessory subunits. Systematic individual or combined elimina tion of high consensus protein kinase A (PKA) sites, by serine to alan ine substitutions at the amino and carboxyl termini of the alpha(1) su bunit, resulted in Ca2+ channel currents indistinguishable from those of wild type channels. Dihydropyridine (DHP)-binding characteristics w ere also unaltered. To explore the possible involvement of nonconsensu s sites, deletion mutants were used. Carboxyl-terminal truncations of the alpha(1) subunit distal to residue 1597 resulted in increased chan nel expression and current amplitudes. Modulation of PKA activity in c ells transfected with the wild type channel or any of the mutants did not alter Ca2+ channel functions suggesting that cardiac Ca2+ channels expressed in these cells behave, in terms of lack of PKA control, lik e Ca2+ channels of smooth muscle cells.