Investigating the Role of a Novel PKA Phosphorylation Site in Cardiac Calcium Channel Function Associated With “Fight-or-Flight” Responses

Aim Calcium influx through the cardiac L-type calcium channel (Cav1.2) is a crucial component of the “Fight-or-Flight” response, a process elicited via β-adrenergic receptor (β-AR) activation. Although importance of Cav1.2 in the “Fight-or-Flight” response is well established, the precise mechanisms remain unresolved. A novel PKA phosphorylation site at serine1458 on human Cav1.2 was previously identified as functionally important. We investigated the effect of mutations targeting the region surrounding the corresponding site (serine 1487) in mouse Cav1.2. Methods Results Mice expressing homozygote S1487E and 21bp del mutations were embryonic lethal. S1487E +/- cardiomyocytes (n=31) had higher basal ICaL compared to wt (n=34; p=0.0024), confirming constitutive activation of the site. Activation kinetics were increased in S1487E +/- cardiomyocytes both prior to (p<0.0001) and after β-AR stimulation (p=0.0012). Wt cardiomyocytes exhibited increased ICaL after β-AR stimulation (p=0.0018). However, this response was significantly reduced in all three mutant models compared to wt (S1487A +/+ : n=33; p<0.0001, S1487E +/- : p<0.0001, 21 bp del +/- : n=16;p=0.0224) Conclusions Introduction of the S1487A +/+ mutation abrogated the characteristic increase in ICaL following β -AR stimulation. This response was also decreased in the S1487E +/- and 21 bp del +/- models, highlighting the importance of Ser1487 in mediating the “Fight-or-Flight” response.