The involvement of cAMP-dependent phosphorylation sites in establishing the basal activity of cardiac L-type Ca²⁺ channels was studied in HEK 293 cells transiently cotransfected with mutants of the human cardiac α₁ and accessory subunits. Systematic individual or combined elimination of high consensus protein kinase A (PKA) sites, by serine to alanine substitutions at the amino and carboxyl termini of the α₁ subunit, resulted in Ca²⁺ channel currents indistinguishable from those of wild type channels. Dihydropyridine (DHP)-binding characteristics were also unaltered. To explore the possible involvement of nonconsensus sites, deletion mutants were used. Carboxyl-terminal truncations of the α₁ subunit distal to residue 1597 resulted in increased channel expression and current amplitudes. Modulation of PKA activity in cells 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, like Ca²⁺ channels of smooth muscle cells.