Role of SERCA3 Protein in Alpha1-Adrenoceptor-mediated Calcium Signaling in Mouse Aortic Function

Introduction Calcium homeostasis plays a major role in vascular tone. Sarco/endoplasmic reticulum Ca2+-ATPases (SERCAs) contribute to generate intracellular calcium stores that are mobilized during functional responses. The SERCA2 family is described as the most important in vascular cells, but SERCA3 has been reported to be co-expressed, with SERCA3a mainly in endothelial cells and SERCA3b in smooth muscle cells. Objective Our aim is to evaluate the role of the SERCA3-dependent calcium signaling in mouse aortic function. Method Aortas were harvested from wild-type (WT) and SERCA3 deficient (SERCA3-KO) male mice and mounted in an organ bath system to assess response to different contractile and relaxant agents. Some rings were also frozen for western blots analysis. Results Among the various contractile agents tested (KCl, phenylephrine (PE), U46619, 5-HT), only the response to the α1-adrenergic agonist PE is impaired in the absence of SERCA3, with a significant decrease in contractile response to cumulative PE concentrations compared to WT aorta (n=5–8; P<0.001, 2-way ANOVA). Interestingly, in the absence of endothelium or in the presence of the NO-synthase inhibitor L-NAME, the difference in contractile response to PE was no longer observed. The response to a single dose of PE is biphasic, with an initial rapid contraction described to be dependent on calcium stores mobilized by IP3, followed by a slow phase due to calcium influx through L-Type Calcium Channel (LTCC) and Store-Operated Calcium Entry (SOCE). In the absence of SERCA3, the fast phase is unchanged, but the amplitude of the slow phase is strongly reduced. Protein expression of the α1-adrenergic receptor, the LTCC (Cav1.2) and the TRPC5 channel are not altered in SERCA3-KO compared to WT aorta. Conclusion These results uncover a specific involvement of SERCA3 in the α1-adrenergic contractile response and suggest a role in the regulating calcium influx under stimulation. Our data suggest a functional crosstalk between the α1-adrenoceptor, SERCA3, the NO pathway and calcium entry via SOCE or LTCC, which is currently under investigation.