Deletion of the C-terminal Phosphorylation Sites in the Cardiac β-Subunit Does Not Affect the Basic β-Adrenergic Response of the Heart and the Cav1.2 Channel

Phosphorylation of the cardiac beta subunit (Ca-v beta(2)) of the Cav1.2 L-type Ca2+ channel complex has been proposed as a mechanism for regulation of L-type Ca2+ channels by various protein kinases including PKA, CaMKII, Akt/PKB, and PKG. To test this hypothesis directly in vivo, we generated a knock-in mouse line with targeted mutation of the Ca-v beta(2) gene by insertion of a stop codon after proline 501 in exon 14 (mouse sequence Cacnb2; beta Stop mouse). This mutation prevented translation of the Ca-v beta(2) C terminus that contains the relevant phosphorylation sites for the above protein kinases. Homozygous cardiac beta Stop mice were born at Mendelian ratio, had a normal life expectancy, and normal basal L-type I-Ca. The regulation of the L-type current by stimulation of the beta-adrenergic receptor was unaffected in vivo and in cardiomyocytes (CMs). beta Stop mice were cross-bred with mice expressing the Cav1.2 gene containing the mutation S1928A (SA beta Stop) or S1512A and S1570A (SF beta Stop) in theCterminus of the alpha(1C) subunit. The beta-adrenergic regulation of the cardiac ICa was unaltered in these mouse lines. In contrast, truncation of the Cav1.2 at Asp1904 abolished beta-adrenergic up-regulation of ICa in murine embryonic CMs. We conclude that phosphorylation of the C-terminal sites in Ca-v beta(2), Ser1928, Ser1512, and Ser1570 of the Cav1.2 protein is functionally not involved in the adrenergic regulation of the murine cardiac Cav1.2 channel.