Sympathetic nervous system triggered activation of protein kinase A, which phosphorylates several targets within cardiomyocytes, augments inotropy, chronotropy, and lusitropy. An important target of β-adrenergic stimulation is the sarcolemmal L-type Ca²⁺ channel, Ca_V1.2, which plays a key role in cardiac excitation–contraction coupling. The molecular mechanisms of β-adrenergic regulation of Ca_V1.2 in cardiomyocytes, however, are incompletely known. Recently, it has been postulated that proteolytic cleavage at Ala¹⁸⁰⁰ and protein kinase A phosphorylation of Ser¹⁷⁰⁰ are required for β-adrenergic modulation of Ca_V1.2.

To assess the role of Ala¹⁸⁰⁰ in the cleavage of α_1C and the role of Ser¹⁷⁰⁰ and Thr¹⁷⁰⁴ in mediating the adrenergic regulation of Ca_V1.2 in the heart.

Using a transgenic approach that enables selective and inducible expression in mice of FLAG-epitope–tagged, dihydropyridine-resistant Ca_V1.2 channels harboring mutations at key regulatory sites, we show that adrenergic regulation of Ca_V1.2 current and fractional shortening of cardiomyocytes do not require phosphorylation of either Ser¹⁷⁰⁰ or Thr¹⁷⁰⁴ of the α_1C subunit. The presence of Ala¹⁸⁰⁰ and the ¹⁷⁹⁸NNAN¹⁸⁰¹ motif in α_1C is not required for proteolytic cleavage of the α_1C C-terminus, and deletion of these residues did not perturb adrenergic modulation of Ca_V1.2 current.

These results show that protein kinase A phosphorylation of α_1C Ser¹⁷⁰⁰ does not have a major role in the sympathetic stimulation of Ca²⁺ current and contraction in the adult murine heart. Moreover, this new transgenic approach enables functional and reproducible screening of α_1C mutants in freshly isolated adult cardiomyocytes in a reliable, timely, cost-effective manner.