Mechanisms of estrogen's effects on calcium signaling in vascular endothelial cells

Abstract

17β‐estradiol (E2) exerts many cardioprotective effects via actions on endothelial cells (ECs). It has been observed that E2 increases Ca2+ signals produced in ECs in response to agonists. However, the underlying mechanisms are unclear. Here we have examined the main components of Ca2+ signaling in primary ECs in response to long‐term exposure to physiological concentrations of E2. E2 treatment for 48 hrs did not affect thapsigargin‐induced internal Ca2+ store release or store‐operated Ca2+ entry. However, we observed a 35% reduction in the activity of the calmodulin (CaM)‐dependent plasma membrane Ca2+‐ATPase (PMCA), the main Ca2+ efflux mechanism in ECs. In contrast, calmodulin (CaM) binding to the PMCA is increased by 50%, while total PMCA expression is not affected. Inhibition of pp60src‐mediated tyrosine phosphorylation of PMCA reveals the effects of E2‐induced increase in CaM binding to the PMCA, demonstrating a 30% increase in PMCA activity in E2‐treated cells. Our results suggest that via pp60src‐dependent phosphorylation of PMCA, estrogen decreases Ca2+ efflux, which provides an explanation for the enhanced Ca2+ signals in ECs exposed to E2.